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-.. COMMENT: %**end of header
-
-.. COMMENT: COPYRIGHT (c) 1989-2013.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-.. COMMENT: Master file for the CPU Supplement
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-.. COMMENT: The following determines which set of the tables and figures we will use.
-
-.. COMMENT: We default to ASCII but if available TeX or HTML versions will
-
-.. COMMENT: be used instead.
-
-.. COMMENT: @clear use-html
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-.. COMMENT: @clear use-tex
-
-.. COMMENT: The following variable says to use texinfo or html for the two column
-
-.. COMMENT: texinfo tables.  For somethings the format does not look good in html.
-
-.. COMMENT: With our adjustment to the left column in TeX, it nearly always looks
-
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-
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-
-.. COMMENT: Title Page Stuff
-
-.. COMMENT: I don't really like having a short title page.  -joel
-
-.. COMMENT: @shorttitlepage RTEMS CPU Architecture Supplement
-
-=================================
-RTEMS CPU Architecture Supplement
-=================================
-
-.. COMMENT: COPYRIGHT (c) 1988-2015.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-.. COMMENT: The following puts a space somewhere on an otherwise empty page so we
-
-.. COMMENT: can force the copyright description onto a left hand page.
-
-COPYRIGHT Â© 1988 - 2015.
-
-On-Line Applications Research Corporation (OAR).
-
-The authors have used their best efforts in preparing
-this material.  These efforts include the development, research,
-and testing of the theories and programs to determine their
-effectiveness.  No warranty of any kind, expressed or implied,
-with regard to the software or the material contained in this
-document is provided.  No liability arising out of the
-application or use of any product described in this document is
-assumed.  The authors reserve the right to revise this material
-and to make changes from time to time in the content hereof
-without obligation to notify anyone of such revision or changes.
-
-The RTEMS Project is hosted at http://www.rtems.org.  Any
-inquiries concerning RTEMS, its related support components, or its
-documentation should be directed to the Community Project hosted athttp://www.rtems.org.
-
-Any inquiries for commercial services including training, support, custom
-development, application development assistance should be directed tohttp://www.rtems.com.
-
-.. COMMENT: This prevents a black box from being printed on "overflow" lines.
-
-.. COMMENT: The alternative is to rework a sentence to avoid this problem.
-
-RTEMS CPU Architecture Supplement
-#################################
-
-.. COMMENT: COPYRIGHT (c) 1989-2011.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Preface
-#######
-
-The Real Time Executive for Multiprocessor Systems
-(RTEMS) is designed to be portable across multiple processor
-architectures.  However, the nature of real-time systems makes
-it essential that the application designer understand certain
-processor dependent implementation details.  These processor
-dependencies include calling convention, board support package
-issues, interrupt processing, exact RTEMS memory requirements,
-performance data, header files, and the assembly language
-interface to the executive.
-
-Each architecture represents a CPU family and usually there are
-a wide variety of CPU models within it.  These models share a
-common Instruction Set Architecture (ISA) which often varies
-based upon some well-defined rules.  There are often
-multiple implementations of the ISA and these may be from
-one or multiple vendors.
-
-On top of variations in the ISA, there may also be variations
-which occur when a CPU core implementation is combined with
-a set of peripherals to form a system on chip.  For example,
-there are many ARM CPU models from numerous semiconductor
-vendors and a wide variety of peripherals.  But at the
-ISA level, they share a common compatibility.
-
-RTEMS depends upon this core similarity across the CPU models
-and leverages that to minimize the source code that is specific
-to any particular CPU core implementation or CPU model.
-
-This manual is separate and distinct from the RTEMS Porting
-Guide.  That manual is a guide on porting RTEMS to a new
-architecture.  This manual is focused on the more mundane
-CPU architecture specific issues that may impact
-application development.  For example, if you need to write
-a subroutine in assembly language, it is critical to understand
-the calling conventions for the target architecture.
-
-The first chapter in this manual describes these issues
-in general terms.  In a sense, it is posing the questions
-one should be aware may need to be answered and understood
-when porting an RTEMS application to a new architecture.
-Each subsequent chapter gives the answers to those questions
-for a particular CPU architecture.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Port Specific Information
-#########################
-
-This chaper provides a general description of the type of
-architecture specific information which is in each of
-the architecture specific chapters that follow.  The outline
-of this chapter is identical to that of the architecture
-specific chapters.
-
-In each of the architecture specific chapters, this
-introductory section will provide an overview of the
-architecture
-
-**Architecture Documents**
-
-In each of the architecture specific chapters, this
-section will provide pointers on where to obtain
-documentation.
-
-CPU Model Dependent Features
-============================
-
-Microprocessors are generally classified into families with a variety of
-CPU models or implementations within that family.  Within a processor
-family, there is a high level of binary compatibility.  This family
-may be based on either an architectural specification or on maintaining
-compatibility with a popular processor.  Recent microprocessor families
-such as the SPARC or PowerPC are based on an architectural specification
-which is independent or any particular CPU model or implementation.
-Older families such as the Motorola 68000 and the Intel x86 evolved as the
-manufacturer strived to produce higher performance processor models which
-maintained binary compatibility with older models.
-
-RTEMS takes advantage of the similarity of the various models within a
-CPU family.  Although the models do vary in significant ways, the high
-level of compatibility makes it possible to share the bulk of the CPU
-dependent executive code across the entire family.  Each processor family
-supported by RTEMS has a list of features which vary between CPU models
-within a family.  For example, the most common model dependent feature
-regardless of CPU family is the presence or absence of a floating point
-unit or coprocessor.  When defining the list of features present on a
-particular CPU model, one simply notes that floating point hardware
-is or is not present and defines a single constant appropriately.
-Conditional compilation is utilized to include the appropriate source
-code for this CPU modelâs feature set.  It is important to note that
-this means that RTEMS is thus compiled using the appropriate feature set
-and compilation flags optimal for this CPU model used.  The alternative
-would be to generate a binary which would execute on all family members
-using only the features which were always present.
-
-The set of CPU model feature macros are defined in the file``cpukit/score/cpu/CPU/rtems/score/cpu.h`` based upon the GNU tools
-multilib variant that is appropriate for the particular CPU model defined
-on the compilation command line.
-
-In each of the architecture specific chapters, this section presents
-the set of features which vary across various implementations of the
-architecture that may be of importance to RTEMS application developers.
-
-The subsections will vary amongst the target architecture chapters as
-the specific features may vary.  However, each port will include a few
-common features such as the CPU Model Name and presence of a hardware
-Floating Point Unit.  The common features are described here.
-
-CPU Model Name
---------------
-
-The macro ``CPU_MODEL_NAME`` is a string which designates
-the name of this CPU model.  For example, for the MC68020
-processor model from the m68k architecture, this macro
-is set to the string "mc68020".
-
-Floating Point Unit
--------------------
-
-In most architectures, the presence of a floating point unit is an option.
-It does not matter whether the hardware floating point support is
-incorporated on-chip or is an external coprocessor as long as it
-appears an FPU per the ISA.  However, if a hardware FPU is not present,
-it is possible that the floating point emulation library for this
-CPU is not reentrant and thus context switched by RTEMS.
-
-RTEMS provides two feature macros to indicate the FPU configuration:
-
-- CPU_HARDWARE_FP
-  is set to TRUE to indicate that a hardware FPU is present.
-
-- CPU_SOFTWARE_FP
-  is set to TRUE to indicate that a hardware FPU is not present and that
-  the FP software emulation will be context switched.
-
-Multilibs
-=========
-
-Newlib and GCC provide several target libraries like the :file:`libc.a`,:file:`libm.a` and :file:`libgcc.a`.  These libraries are artifacts of the GCC
-build process.  Newlib is built together with GCC.  To provide optimal support
-for various chip derivatives and instruction set revisions multiple variants of
-these libraries are available for each architecture.  For example one set may
-use software floating point support and another set may use hardware floating
-point instructions.  These sets of libraries are called *multilibs*.  Each
-library set corresponds to an application binary interface (ABI) and
-instruction set.
-
-A multilib variant can be usually detected via built-in compiler defines at
-compile-time.  This mechanism is used by RTEMS to select for example the
-context switch support for a particular BSP.  The built-in compiler defines
-corresponding to multilibs are the only architecture specific defines allowed
-in the ``cpukit`` area of the RTEMS sources.
-
-Invoking the GCC with the ``-print-multi-lib`` option lists the available
-multilibs.  Each line of the output describes one multilib variant.  The
-default variant is denoted by ``.`` which is selected when no or
-contradicting GCC machine options are selected.  The multilib selection for a
-target is specified by target makefile fragments (see file :file:`t-rtems` in
-the GCC sources and section`The Target Makefile Fragment <https://gcc.gnu.org/onlinedocs/gccint/Target-Fragment.html#Target-Fragment>`_
-in the `GCC Internals Manual <https://gcc.gnu.org/onlinedocs/gccint/>`_.
-
-Calling Conventions
-===================
-
-Each high-level language compiler generates subroutine entry and exit
-code based upon a set of rules known as the compilerâs calling convention.
-These rules address the following issues:
-
-- register preservation and usage
-
-- parameter passing
-
-- call and return mechanism
-
-A compilerâs calling convention is of importance when
-interfacing to subroutines written in another language either
-assembly or high-level.  Even when the high-level language and
-target processor are the same, different compilers may use
-different calling conventions.  As a result, calling conventions
-are both processor and compiler dependent.
-
-Calling Mechanism
------------------
-
-In each of the architecture specific chapters, this subsection will
-describe the instruction(s) used to perform a *normal* subroutine
-invocation.  All RTEMS directives are invoked as *normal* C language
-functions so it is important to the user application to understand the
-call and return mechanism.
-
-Register Usage
---------------
-
-In each of the architecture specific chapters, this subsection will
-detail the set of registers which are *NOT* preserved across subroutine
-invocations.  The registers which are not preserved are assumed to be
-available for use as scratch registers.  Therefore, the contents of these
-registers should not be assumed upon return from any RTEMS directive.
-
-In some architectures, there may be a set of registers made available
-automatically as a side-effect of the subroutine invocation
-mechanism.
-
-Parameter Passing
------------------
-
-In each of the architecture specific chapters, this subsection will
-describe the mechanism by which the parameters or arguments are passed
-by the caller to a subroutine.  In some architectures, all parameters
-are passed on the stack while in others some are passed in registers.
-
-User-Provided Routines
-----------------------
-
-All user-provided routines invoked by RTEMS, such as
-user extensions, device drivers, and MPCI routines, must also
-adhere to these calling conventions.
-
-Memory Model
-============
-
-A processor may support any combination of memory
-models ranging from pure physical addressing to complex demand
-paged virtual memory systems.  RTEMS supports a flat memory
-model which ranges contiguously over the processorâs allowable
-address space.  RTEMS does not support segmentation or virtual
-memory of any kind.  The appropriate memory model for RTEMS
-provided by the targeted processor and related characteristics
-of that model are described in this chapter.
-
-Flat Memory Model
------------------
-
-Most RTEMS target processors can be initialized to support a flat address
-space.  Although the size of addresses varies between architectures, on
-most RTEMS targets, an address is 32-bits wide which defines addresses
-ranging from 0x00000000 to 0xFFFFFFFF (4 gigabytes).  Each address is
-represented by a 32-bit value and is byte addressable.  The address may be
-used to reference a single byte, word (2-bytes), or long word (4 bytes).
-Memory accesses within this address space may be performed in little or
-big endian fashion.
-
-On smaller CPU architectures supported by RTEMS, the address space
-may only be 20 or 24 bits wide.
-
-If the CPU model has support for virtual memory or segmentation, it is
-the responsibility of the Board Support Package (BSP) to initialize the
-MMU hardware to perform address translations which correspond to flat
-memory model.
-
-In each of the architecture specific chapters, this subsection will
-describe any architecture characteristics that differ from this general
-description.
-
-Interrupt Processing
-====================
-
-Different types of processors respond to the occurrence of an interrupt
-in its own unique fashion. In addition, each processor type provides
-a control mechanism to allow for the proper handling of an interrupt.
-The processor dependent response to the interrupt modifies the current
-execution state and results in a change in the execution stream.  Most
-processors require that an interrupt handler utilize some special control
-mechanisms to return to the normal processing stream.  Although RTEMS
-hides many of the processor dependent details of interrupt processing,
-it is important to understand how the RTEMS interrupt manager is mapped
-onto the processorâs unique architecture.
-
-RTEMS supports a dedicated interrupt stack for all architectures.
-On architectures with hardware support for a dedicated interrupt stack,
-it will be initialized such that when an interrupt occurs, the processor
-automatically switches to this dedicated stack.  On architectures without
-hardware support for a dedicated interrupt stack which is separate from
-those of the tasks, RTEMS will support switching to a dedicated stack
-for interrupt processing.
-
-Without a dedicated interrupt stack, every task in
-the system MUST have enough stack space to accommodate the worst
-case stack usage of that particular task and the interrupt
-service routines COMBINED.  By supporting a dedicated interrupt
-stack, RTEMS significantly lowers the stack requirements for
-each task.
-
-A nested interrupt is processed similarly with the exception that since
-the CPU is already executing on the interrupt stack, there is no need
-to switch to the interrupt stack.
-
-In some configurations, RTEMS allocates the interrupt stack from the
-Workspace Area.  The amount of memory allocated for the interrupt stack
-is user configured and based upon the ``confdefs.h`` parameter``CONFIGURE_INTERRUPT_STACK_SIZE``.  This parameter is described
-in detail in the Configuring a System chapter of the Userâs Guide.
-On configurations in which RTEMS allocates the interrupt stack, during
-the initialization process, RTEMS will also install its interrupt stack.
-In other configurations, the interrupt stack is allocated and installed
-by the Board Support Package (BSP).
-
-In each of the architecture specific chapters, this section discesses
-the interrupt response and control mechanisms of the architecture as
-they pertain to RTEMS.
-
-Vectoring of an Interrupt Handler
----------------------------------
-
-In each of the architecture specific chapters, this subsection will
-describe the architecture specific details of the interrupt vectoring
-process.  In particular, it should include a description of the
-Interrupt Stack Frame (ISF).
-
-Interrupt Levels
-----------------
-
-In each of the architecture specific chapters, this subsection will
-describe how the interrupt levels available on this particular architecture
-are mapped onto the 255 reserved in the task mode.  The interrupt level
-value of zero (0) should always mean that interrupts are enabled.
-
-Any use of an  interrupt level that is is not undefined on a particular
-architecture may result in behavior that is unpredictable.
-
-Disabling of Interrupts by RTEMS
---------------------------------
-
-During the execution of directive calls, critical sections of code may
-be executed.  When these sections are encountered, RTEMS disables all
-external interrupts before the execution of this section and restores
-them to the previous level upon completion of the section.  RTEMS has
-been optimized to ensure that interrupts are disabled for the shortest
-number of instructions possible.  Since the precise number of instructions
-and their execution time varies based upon target CPU family, CPU model,
-board memory speed, compiler version, and optimization level, it is
-not practical to provide the precise number for all possible RTEMS
-configurations.
-
-Historically, the measurements were made by hand analyzing and counting
-the execution time of instruction sequences during interrupt disable
-critical sections.  For reference purposes, on a 16 Mhz Motorola
-MC68020, the maximum interrupt disable period was typically approximately
-ten (10) to thirteen (13) microseconds.  This architecture was memory bound
-and had a slow bit scan instruction.  In contrast, during the same
-period a 14 Mhz SPARC would have a worst case disable time of approximately
-two (2) to three (3) microseconds because it had a single cycle bit scan
-instruction and used fewer cycles for memory accesses.
-
-If you are interested in knowing the worst case execution time for
-a particular version of RTEMS, please contact OAR Corporation and
-we will be happy to product the results as a consulting service.
-
-Non-maskable interrupts (NMI) cannot be disabled, and
-ISRs which execute at this level MUST NEVER issue RTEMS system
-calls.  If a directive is invoked, unpredictable results may
-occur due to the inability of RTEMS to protect its critical
-sections.  However, ISRs that make no system calls may safely
-execute as non-maskable interrupts.
-
-Default Fatal Error Processing
-==============================
-
-Upon detection of a fatal error by either the application or RTEMS during
-initialization the ``rtems_fatal_error_occurred`` directive supplied
-by the Fatal Error Manager is invoked.  The Fatal Error Manager will
-invoke the user-supplied fatal error handlers.  If no user-supplied
-handlers are configured or all of them return without taking action to
-shutdown the processor or reset, a default fatal error handler is invoked.
-
-Most of the action performed as part of processing the fatal error are
-described in detail in the Fatal Error Manager chapter in the Userâs
-Guide.  However, the if no user provided extension or BSP specific fatal
-error handler takes action, the final default action is to invoke a
-CPU architecture specific function.  Typically this function disables
-interrupts and halts the processor.
-
-In each of the architecture specific chapters, this describes the precise
-operations of the default CPU specific fatal error handler.
-
-Symmetric Multiprocessing
-=========================
-
-This section contains information about the Symmetric Multiprocessing (SMP)
-status of a particular architecture.
-
-Thread-Local Storage
-====================
-
-In order to support thread-local storage (TLS) the CPU port must implement the
-facilities mandated by the application binary interface (ABI) of the CPU
-architecture.  The CPU port must initialize the TLS area in the``_CPU_Context_Initialize()`` function.  There are support functions available
-via ``#include <rtems/score/tls.h>`` which implement Variants I and II
-according to Ulrich Drepper, *ELF Handling For Thread-Local Storage*.
-
-``_TLS_TCB_at_area_begin_initialize()``
-    Uses Variant I, TLS offsets emitted by linker takes the TCB into account.  For
-    a reference implementation see :file:`cpukit/score/cpu/arm/cpu.c`.
-
-``_TLS_TCB_before_TLS_block_initialize()``
-    Uses Variant I, TLS offsets emitted by linker neglects the TCB.  For a
-    reference implementation see:file:`c/src/lib/libcpu/powerpc/new-exceptions/cpu.c`.
-
-``_TLS_TCB_after_TLS_block_initialize()``
-    Uses Variant II.  For a reference implementation see:file:`cpukit/score/cpu/sparc/cpu.c`.
-
-The board support package (BSP) must provide the following sections and symbols
-in its linker command file:
-.. code:: c
-
-    .tdata : {
-    _TLS_Data_begin = .;
-    \*(.tdata .tdata.* .gnu.linkonce.td.*)
-    _TLS_Data_end = .;
-    }
-    .tbss : {
-    _TLS_BSS_begin = .;
-    \*(.tbss .tbss.* .gnu.linkonce.tb.*) \*(.tcommon)
-    _TLS_BSS_end = .;
-    }
-    _TLS_Data_size = _TLS_Data_end - _TLS_Data_begin;
-    _TLS_Data_begin = _TLS_Data_size != 0 ? _TLS_Data_begin : _TLS_BSS_begin;
-    _TLS_Data_end = _TLS_Data_size != 0 ? _TLS_Data_end : _TLS_BSS_begin;
-    _TLS_BSS_size = _TLS_BSS_end - _TLS_BSS_begin;
-    _TLS_Size = _TLS_BSS_end - _TLS_Data_begin;
-    _TLS_Alignment = MAX (ALIGNOF (.tdata), ALIGNOF (.tbss));
-
-CPU counter
-===========
-
-The CPU support must implement the CPU counter interface.  A CPU counter is
-some free-running counter.  It ticks usually with a frequency close to the CPU
-or system bus clock.  On some architectures the actual implementation is board
-support package dependent.  The CPU counter is used for profiling of low-level
-functions.  It is also used to implement two busy wait functions``rtems_counter_delay_ticks()`` and ``rtems_counter_delay_nanoseconds()``
-which may be used in device drivers.  It may be also used as an entropy source
-for random number generators.
-
-The CPU counter interface uses a CPU port specific unsigned integer type``CPU_Counter_ticks`` to represent CPU counter values.  The CPU port must
-provide the following two functions
-
-- ``_CPU_Counter_read()`` to read the current CPU counter value, and
-
-- ``_CPU_Counter_difference()`` to get the difference between two CPU
-  counter values.
-
-Interrupt Profiling
-===================
-
-The RTEMS profiling needs support by the CPU port for the interrupt entry and
-exit times.  In case profiling is enabled via the RTEMS build configuration
-option ``--enable-profiling`` (in this case the pre-processor symbol``RTEMS_PROFILING`` is defined) the CPU port may provide data for the
-interrupt entry and exit times of the outer-most interrupt.  The CPU port can
-feed interrupt entry and exit times with the``_Profiling_Outer_most_interrupt_entry_and_exit()`` function
-(``#include <rtems/score/profiling.h>``).  For an example please have a look
-at ``cpukit/score/cpu/arm/arm_exc_interrupt.S``.
-
-Board Support Packages
-======================
-
-An RTEMS Board Support Package (BSP) must be designed to support a
-particular processor model and target board combination.
-
-In each of the architecture specific chapters, this section will present
-a discussion of architecture specific BSP issues.   For more information
-on developing a BSP, refer to BSP and Device Driver Development Guide
-and the chapter titled Board Support Packages in the RTEMS
-Applications Userâs Guide.
-
-System Reset
-------------
-
-An RTEMS based application is initiated or re-initiated when the processor
-is reset or transfer is passed to it from a boot monitor or ROM monitor.
-
-In each of the architecture specific chapters, this subsection describes
-the actions that the BSP must tak assuming the application gets control
-when the microprocessor is reset.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-ARM Specific Information
-########################
-
-This chapter discusses the`ARM architecture <http://en.wikipedia.org/wiki/ARM_architecture>`_
-dependencies in this port of RTEMS.  The ARMv4T (and compatible), ARMv7-A,
-ARMv7-R and ARMv7-M architecture versions are supported by RTEMS.  Processors
-with a MMU use a static configuration which is set up during system start.  SMP
-is supported.
-
-**Architecture Documents**
-
-For information on the ARM architecture refer to the`ARM Infocenter <http://infocenter.arm.com>`_.
-
-CPU Model Dependent Features
-============================
-
-This section presents the set of features which vary
-across ARM implementations and are of importance to RTEMS.  The set of CPU
-model feature macros are defined in the file:file:`cpukit/score/cpu/arm/rtems/score/arm.h` based upon the particular CPU
-model flags specified on the compilation command line.
-
-CPU Model Name
---------------
-
-The macro ``CPU_MODEL_NAME`` is a string which designates
-the architectural level of this CPU model.  See in:file:`cpukit/score/cpu/arm/rtems/score/arm.h` for the values.
-
-Count Leading Zeroes Instruction
---------------------------------
-
-The ARMv5 and later has the count leading zeroes ``clz`` instruction which
-could be used to speed up the find first bit operation.  The use of this
-instruction should significantly speed up the scheduling associated with a
-thread blocking.  This is currently not used.
-
-Floating Point Unit
--------------------
-
-The following floating point units are supported.
-
-- VFPv3-D32/NEON (for example available on Cortex-A processors)
-
-- VFPv3-D16 (for example available on Cortex-R processors)
-
-- FPv4-SP-D16 (for example available on Cortex-M processors)
-
-Multilibs
-=========
-
-The following multilibs are available:
-
-# ``.``: ARMv4T, ARM instruction set
-
-# ``thumb``: ARMv4T, Thumb-1 instruction set
-
-# ``thumb/armv6-m``: ARMv6M, subset of Thumb-2 instruction set
-
-# ``thumb/armv7-a``: ARMv7-A, Thumb-2 instruction set
-
-# ``thumb/armv7-a/neon/hard``: ARMv7-A, Thumb-2 instruction set with
-  hard-float ABI Neon and VFP-D32 support
-
-# ``thumb/armv7-r``: ARMv7-R, Thumb-2 instruction set
-
-# ``thumb/armv7-r/vfpv3-d16/hard``: ARMv7-R, Thumb-2 instruction set
-  with hard-float ABI VFP-D16 support
-
-# ``thumb/armv7-m``: ARMv7-M, Thumb-2 instruction set with hardware
-  integer division (SDIV/UDIV)
-
-# ``thumb/armv7-m/fpv4-sp-d16``: ARMv7-M, Thumb-2 instruction set with
-  hardware integer division (SDIV/UDIV) and hard-float ABI FPv4-SP support
-
-# ``eb/thumb/armv7-r``: ARMv7-R, Big-endian Thumb-2 instruction set
-
-# ``eb/thumb/armv7-r/vfpv3-d16/hard``: ARMv7-R, Big-endian Thumb-2
-  instruction set with hard-float ABI VFP-D16 support
-
-Multilib 1. and 2. support the standard ARM7TDMI and ARM926EJ-S targets.
-
-Multilib 3. supports the Cortex-M0 and Cortex-M1 cores.
-
-Multilib 8. supports the Cortex-M3 and Cortex-M4 cores, which have a special
-hardware integer division instruction (this is not present in the A and R
-profiles).
-
-Multilib 9. supports the Cortex-M4 cores with a floating point unit.
-
-Multilib 4. and 5. support the Cortex-A processors.
-
-Multilib 6., 7., 10. and 11. support the Cortex-R processors.  Here also
-big-endian variants are available.
-
-Use for example the following GCC options
-.. code:: c
-
-    -mthumb -march=armv7-a -mfpu=neon -mfloat-abi=hard -mtune=cortex-a9
-
-to build an application or BSP for the ARMv7-A architecture and tune the code
-for a Cortex-A9 processor.  It is important to select the options used for the
-multilibs. For example
-.. code:: c
-
-    -mthumb -mcpu=cortex-a9
-
-alone will not select the ARMv7-A multilib.
-
-Calling Conventions
-===================
-
-Please refer to the`Procedure Call Standard for the ARM Architecture <http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042c/IHI0042C_aapcs.pdf>`_.
-
-Memory Model
-============
-
-A flat 32-bit memory model is supported.  The board support package must take
-care about the MMU if necessary.
-
-Interrupt Processing
-====================
-
-The ARMv4T (and compatible) architecture has seven exception types:
-
-- Reset
-
-- Undefined
-
-- Software Interrupt (SWI)
-
-- Prefetch Abort
-
-- Data Abort
-
-- Interrupt (IRQ)
-
-- Fast Interrupt (FIQ)
-
-Of these types only the IRQ has explicit operating system support.  It is
-intentional that the FIQ is not supported by the operating system.  Without
-operating system support for the FIQ it is not necessary to disable them during
-critical sections of the system.
-
-The ARMv7-M architecture has a completely different exception model.  Here
-interrupts are disabled with a write of 0x80 to the ``basepri_max``
-register.  This means that all exceptions and interrupts with a priority value
-of greater than or equal to 0x80 are disabled.  Thus exceptions and interrupts
-with a priority value of less than 0x80 are non-maskable with respect to the
-operating system and therefore must not use operating system services.  Several
-support libraries of chip vendors implicitly shift the priority value somehow
-before the value is written to the NVIC IPR register.  This can easily lead to
-confusion.
-
-Interrupt Levels
-----------------
-
-There are exactly two interrupt levels on ARM with respect to RTEMS.  Level
-zero corresponds to interrupts enabled.  Level one corresponds to interrupts
-disabled.
-
-Interrupt Stack
----------------
-
-The board support package must initialize the interrupt stack. The memory for
-the stacks is usually reserved in the linker script.
-
-Default Fatal Error Processing
-==============================
-
-The default fatal error handler for this architecture performs the
-following actions:
-
-- disables operating system supported interrupts (IRQ),
-
-- places the error code in ``r0``, and
-
-- executes an infinite loop to simulate a halt processor instruction.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is supported on ARMv7-A.  Available platforms are the Altera Cyclone V and
-the Xilinx Zynq.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is supported.
-
-.. COMMENT: COPYRIGHT (c) 1988-2009.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Atmel AVR Specific Information
-##############################
-
-This chapter discusses the AVR architecture dependencies in this
-port of RTEMS.
-
-**Architecture Documents**
-
-For information on the AVR architecture, refer to the following
-documents available from Atmel.
-
-TBD
-
-- See other CPUs for documentation reference formatting examples.
-
-CPU Model Dependent Features
-============================
-
-CPUs of the AVR 53X only differ in the peripherals and thus in the
-device drivers. This port does not yet support the 56X dual core variants.
-
-Count Leading Zeroes Instruction
---------------------------------
-
-The AVR CPU has the XXX instruction which could be used to speed
-up the find first bit operation.  The use of this instruction should
-significantly speed up the scheduling associated with a thread blocking.
-
-Calling Conventions
-===================
-
-Processor Background
---------------------
-
-The AVR architecture supports a simple call and return mechanism.
-A subroutine is invoked via the call (``call``) instruction.
-This instruction saves the return address in the ``RETS`` register
-and transfers the execution to the given address.
-
-It is the called funcions responsability to use the link instruction
-to reserve space on the stack for the local variables.  Returning from
-a subroutine is done by using the RTS (``RTS``) instruction which
-loads the PC with the adress stored in RETS.
-
-It is is important to note that the ``call`` instruction does not
-automatically save or restore any registers.  It is the responsibility
-of the high-level language compiler to define the register preservation
-and usage convention.
-
-Register Usage
---------------
-
-A called function may clobber all registers, except RETS, R4-R7, P3-P5,
-FP and SP.  It may also modify the first 12 bytes in the callerÃ¢ÂÂs stack
-frame which is used as an argument area for the first three arguments
-(which are passed in R0...R3 but may be placed on the stack by the
-called function).
-
-Parameter Passing
------------------
-
-RTEMS assumes that the AVR GCC calling convention is followed.
-The first three parameters are stored in registers R0, R1, and R2.
-All other parameters are put pushed on the stack.  The result is returned
-through register R0.
-
-Memory Model
-============
-
-The AVR family architecutre support a single unified 4 GB byte
-address space using 32-bit addresses. It maps all resources like internal
-and external memory and IO registers into separate sections of this
-common address space.
-
-The AVR architcture supports some form of memory
-protection via its Memory Management Unit. Since the
-AVR port runs in supervisior mode this memory
-protection mechanisms are not used.
-
-Interrupt Processing
-====================
-
-Discussed in this chapter are the AVRâs interrupt response and
-control mechanisms as they pertain to RTEMS.
-
-Vectoring of an Interrupt Handler
----------------------------------
-
-TBD
-
-Disabling of Interrupts by RTEMS
---------------------------------
-
-During interrupt disable critical sections, RTEMS disables interrupts to
-level N (N) before the execution of this section and restores them
-to the previous level upon completion of the section. RTEMS uses the
-instructions CLI and STI to enable and disable Interrupts. Emulation,
-Reset, NMI and Exception Interrupts are never disabled.
-
-Interrupt Stack
----------------
-
-The AVR Architecture works with two different kind of stacks,
-User and Supervisor Stack. Since RTEMS and its Application run
-in supervisor mode, all interrupts will use the interrupted
-tasks stack for execution.
-
-Default Fatal Error Processing
-==============================
-
-The default fatal error handler for the AVR performs the following
-actions:
-
-- disables processor interrupts,
-
-- places the error code in *r0*, and
-
-- executes an infinite loop (``while(0);`` to
-  simulate a halt processor instruction.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is not supported due to a broken tool chain.
-
-Board Support Packages
-======================
-
-System Reset
-------------
-
-TBD
-
-.. COMMENT: COPYRIGHT (c) 1988-2006.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Blackfin Specific Information
-#############################
-
-This chapter discusses the Blackfin architecture dependencies in this
-port of RTEMS.
-
-**Architecture Documents**
-
-For information on the Blackfin architecture, refer to the following
-documents available from Analog Devices.
-
-TBD
-
-- *"ADSP-BF533 Blackfin Processor Hardware Reference."*:file:`http://www.analog.com/UploadedFiles/Associated_Docs/892485982bf533_hwr.pdf`
-
-CPU Model Dependent Features
-============================
-
-CPUs of the Blackfin 53X only differ in the peripherals and thus in the
-device drivers. This port does not yet support the 56X dual core variants.
-
-Count Leading Zeroes Instruction
---------------------------------
-
-The Blackfin CPU has the BITTST instruction which could be used to speed
-up the find first bit operation.  The use of this instruction should
-significantly speed up the scheduling associated with a thread blocking.
-
-Calling Conventions
-===================
-
-This section is heavily based on content taken from the Blackfin uCLinux
-documentation wiki which is edited by Analog Devices and Arcturus
-Networks.  :file:`http://docs.blackfin.uclinux.org/`
-
-Processor Background
---------------------
-
-The Blackfin architecture supports a simple call and return mechanism.
-A subroutine is invoked via the call (``call``) instruction.
-This instruction saves the return address in the ``RETS`` register
-and transfers the execution to the given address.
-
-It is the called funcions responsability to use the link instruction
-to reserve space on the stack for the local variables.  Returning from
-a subroutine is done by using the RTS (``RTS``) instruction which
-loads the PC with the adress stored in RETS.
-
-It is is important to note that the ``call`` instruction does not
-automatically save or restore any registers.  It is the responsibility
-of the high-level language compiler to define the register preservation
-and usage convention.
-
-Register Usage
---------------
-
-A called function may clobber all registers, except RETS, R4-R7, P3-P5,
-FP and SP.  It may also modify the first 12 bytes in the callerÃ¢ÂÂs stack
-frame which is used as an argument area for the first three arguments
-(which are passed in R0...R3 but may be placed on the stack by the
-called function).
-
-Parameter Passing
------------------
-
-RTEMS assumes that the Blackfin GCC calling convention is followed.
-The first three parameters are stored in registers R0, R1, and R2.
-All other parameters are put pushed on the stack.  The result is returned
-through register R0.
-
-Memory Model
-============
-
-The Blackfin family architecutre support a single unified 4 GB byte
-address space using 32-bit addresses. It maps all resources like internal
-and external memory and IO registers into separate sections of this
-common address space.
-
-The Blackfin architcture supports some form of memory
-protection via its Memory Management Unit. Since the
-Blackfin port runs in supervisior mode this memory
-protection mechanisms are not used.
-
-Interrupt Processing
-====================
-
-Discussed in this chapter are the Blackfinâs interrupt response and
-control mechanisms as they pertain to RTEMS. The Blackfin architecture
-support 16 kinds of interrupts broken down into Core and general-purpose
-interrupts.
-
-Vectoring of an Interrupt Handler
----------------------------------
-
-RTEMS maps levels 0 -15 directly to Blackfins event vectors EVT0 -
-EVT15. Since EVT0 - EVT6 are core events and it is suggested to use
-EVT15 and EVT15 for Software interrupts, 7 Interrupts (EVT7-EVT13)
-are left for periferical use.
-
-When installing an RTEMS interrupt handler RTEMS installs a generic
-Interrupt Handler which saves some context and enables nested interrupt
-servicing and then vectors to the users interrupt handler.
-
-Disabling of Interrupts by RTEMS
---------------------------------
-
-During interrupt disable critical sections, RTEMS disables interrupts to
-level four (4) before the execution of this section and restores them
-to the previous level upon completion of the section. RTEMS uses the
-instructions CLI and STI to enable and disable Interrupts. Emulation,
-Reset, NMI and Exception Interrupts are never disabled.
-
-Interrupt Stack
----------------
-
-The Blackfin Architecture works with two different kind of stacks,
-User and Supervisor Stack. Since RTEMS and its Application run
-in supervisor mode, all interrupts will use the interrupted
-tasks stack for execution.
-
-Default Fatal Error Processing
-==============================
-
-The default fatal error handler for the Blackfin performs the following
-actions:
-
-- disables processor interrupts,
-
-- places the error code in *r0*, and
-
-- executes an infinite loop (``while(0);`` to
-  simulate a halt processor instruction.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is not implemented.
-
-Board Support Packages
-======================
-
-System Reset
-------------
-
-TBD
-
-.. COMMENT: Copyright (c) 2015 University of York.
-
-.. COMMENT: Hesham ALMatary <hmka501@york.ac.uk>
-
-Epiphany Specific Information
-#############################
-
-This chapter discusses the`Epiphany Architecture <http://adapteva.com/docs/epiphany_sdk_ref.pdf>`_
-dependencies in this port of RTEMS. Epiphany is a chip that can come with 16 and
-64 cores, each of which can run RTEMS separately or they can work together to
-run a SMP RTEMS application.
-
-**Architecture Documents**
-
-For information on the Epiphany architecture refer to the`Epiphany Architecture Reference <http://adapteva.com/docs/epiphany_arch_ref.pdf>`_.
-
-Calling Conventions
-===================
-
-Please refer to the`Epiphany SDK <http://adapteva.com/docs/epiphany_sdk_ref.pdf>`_
-Appendix A: Application Binary Interface
-
-Floating Point Unit
--------------------
-
-A floating point unit is currently not supported.
-
-Memory Model
-============
-
-A flat 32-bit memory model is supported, no caches. Each core has its own 32 KiB
-strictly ordered local memory along with an access to a shared 32 MiB external
-DRAM.
-
-Interrupt Processing
-====================
-
-Every Epiphany core has 10 exception types:
-
-- Reset
-
-- Software Exception
-
-- Data Page Fault
-
-- Timer 0
-
-- Timer 1
-
-- Message Interrupt
-
-- DMA0 Interrupt
-
-- DMA1 Interrupt
-
-- WANT Interrupt
-
-- User Interrupt
-
-Interrupt Levels
-----------------
-
-There are only two levels: interrupts enabled and interrupts disabled.
-
-Interrupt Stack
----------------
-
-The Epiphany RTEMS port uses a dedicated software interrupt stack.
-The stack for interrupts is allocated during interrupt driver initialization.
-When an  interrupt is entered, the _ISR_Handler routine is responsible for
-switching from the interrupted task stack to RTEMS software interrupt stack.
-
-Default Fatal Error Processing
-==============================
-
-The default fatal error handler for this architecture performs the
-following actions:
-
-- disables operating system supported interrupts (IRQ),
-
-- places the error code in ``r0``, and
-
-- executes an infinite loop to simulate a halt processor instruction.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Intel/AMD x86 Specific Information
-##################################
-
-This chapter discusses the Intel x86 architecture dependencies
-in this port of RTEMS.  This family has multiple implementations
-from multiple vendors and suffers more from having evolved rather
-than being designed for growth.
-
-For information on the i386 processor, refer to the
-following documents:
-
-- *386 Programmerâs Reference Manual, Intel, Order No.  230985-002*.
-
-- *386 Microprocessor Hardware Reference Manual, Intel,
-  Order No. 231732-003*.
-
-- *80386 System Software Writerâs Guide, Intel, Order No.  231499-001*.
-
-- *80387 Programmerâs Reference Manual, Intel, Order No.  231917-001*.
-
-CPU Model Dependent Features
-============================
-
-This section presents the set of features which vary
-across i386 implementations and are of importance to RTEMS.
-The set of CPU model feature macros are defined in the file``cpukit/score/cpu/i386/i386.h`` based upon the particular CPU
-model specified on the compilation command line.
-
-bswap Instruction
------------------
-
-The macro ``I386_HAS_BSWAP`` is set to 1 to indicate that
-this CPU model has the ``bswap`` instruction which
-endian swaps a thirty-two bit quantity.  This instruction
-appears to be present in all CPU models
-i486âs and above.
-
-Calling Conventions
-===================
-
-Processor Background
---------------------
-
-The i386 architecture supports a simple yet effective
-call and return mechanism.  A subroutine is invoked via the call
-(``call``) instruction.  This instruction pushes the return address
-on the stack.  The return from subroutine (``ret``) instruction pops
-the return address off the current stack and transfers control
-to that instruction.  It is is important to note that the i386
-call and return mechanism does not automatically save or restore
-any registers.  It is the responsibility of the high-level
-language compiler to define the register preservation and usage
-convention.
-
-Calling Mechanism
------------------
-
-All RTEMS directives are invoked using a call instruction and return to
-the user application via the ret instruction.
-
-Register Usage
---------------
-
-As discussed above, the call instruction does not automatically save
-any registers.  RTEMS uses the registers EAX, ECX, and EDX as scratch
-registers.  These registers are not preserved by RTEMS directives
-therefore, the contents of these registers should not be assumed upon
-return from any RTEMS directive.
-
-Parameter Passing
------------------
-
-RTEMS assumes that arguments are placed on the
-current stack before the directive is invoked via the call
-instruction.  The first argument is assumed to be closest to the
-return address on the stack.  This means that the first argument
-of the C calling sequence is pushed last.  The following
-pseudo-code illustrates the typical sequence used to call a
-RTEMS directive with three (3) arguments:
-.. code:: c
-
-    push third argument
-    push second argument
-    push first argument
-    invoke directive
-    remove arguments from the stack
-
-The arguments to RTEMS are typically pushed onto the
-stack using a push instruction.  These arguments must be removed
-from the stack after control is returned to the caller.  This
-removal is typically accomplished by adding the size of the
-argument list in bytes to the stack pointer.
-
-Memory Model
-============
-
-Flat Memory Model
------------------
-
-RTEMS supports the i386 protected mode, flat memory
-model with paging disabled.  In this mode, the i386
-automatically converts every address from a logical to a
-physical address each time it is used.  The i386 uses
-information provided in the segment registers and the Global
-Descriptor Table to convert these addresses.  RTEMS assumes the
-existence of the following segments:
-
-- a single code segment at protection level (0) which
-  contains all application and executive code.
-
-- a single data segment at protection level zero (0) which
-  contains all application and executive data.
-
-The i386 segment registers and associated selectors
-must be initialized when the initialize_executive directive is
-invoked.  RTEMS treats the segment registers as system registers
-and does not modify or context switch them.
-
-This i386 memory model supports a flat 32-bit address
-space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
-gigabytes).  Each address is represented by a 32-bit value and
-is byte addressable.  The address may be used to reference a
-single byte, half-word (2-bytes), or word (4 bytes).
-
-Interrupt Processing
-====================
-
-Although RTEMS hides many of the processor
-dependent details of interrupt processing, it is important to
-understand how the RTEMS interrupt manager is mapped onto the
-processorâs unique architecture. Discussed in this chapter are
-the the processorâs response and control mechanisms as they
-pertain to RTEMS.
-
-Vectoring of Interrupt Handler
-------------------------------
-
-Although the i386 supports multiple privilege levels,
-RTEMS and all user software executes at privilege level 0.  This
-decision was made by the RTEMS designers to enhance
-compatibility with processors which do not provide sophisticated
-protection facilities like those of the i386.  This decision
-greatly simplifies the discussion of i386 processing, as one
-need only consider interrupts without privilege transitions.
-
-Upon receipt of an interrupt  the i386 automatically
-performs the following actions:
-
-- pushes the EFLAGS register
-
-- pushes the far address of the interrupted instruction
-
-- vectors to the interrupt service routine (ISR).
-
-A nested interrupt is processed similarly by the
-i386.
-
-Interrupt Stack Frame
----------------------
-
-The structure of the Interrupt Stack Frame for the
-i386 which is placed on the interrupt stack by the processor in
-response to an interrupt is as follows:
-
-+----------------------+-------+
-| Old EFLAGS Register  | ESP+8 |
-+----------+-----------+-------+
-|   UNUSED |  Old CS   | ESP+4 |
-+----------+-----------+-------+
-|       Old EIP        | ESP   |
-+----------------------+-------+
-
-
-Interrupt Levels
-----------------
-
-Although RTEMS supports 256 interrupt levels, the
-i386 only supports two â enabled and disabled.  Interrupts are
-enabled when the interrupt-enable flag (IF) in the extended
-flags (EFLAGS) is set.  Conversely, interrupt processing is
-inhibited when the IF is cleared.  During a non-maskable
-interrupt, all other interrupts, including other non-maskable
-ones, are inhibited.
-
-RTEMS interrupt levels 0 and 1 such that level zero
-(0) indicates that interrupts are fully enabled and level one
-that interrupts are disabled.  All other RTEMS interrupt levels
-are undefined and their behavior is unpredictable.
-
-Interrupt Stack
----------------
-
-The i386 family does not support a dedicated hardware
-interrupt stack.  On this processor, RTEMS allocates and manages
-a dedicated interrupt stack.  As part of vectoring a non-nested
-interrupt service routine, RTEMS switches from the stack of the
-interrupted task to a dedicated interrupt stack.  When a
-non-nested interrupt returns, RTEMS switches back to the stack
-of the interrupted stack.  The current stack pointer is not
-altered by RTEMS on nested interrupt.
-
-Default Fatal Error Processing
-==============================
-
-The default fatal error handler for this architecture disables processor
-interrupts, places the error code in EAX, and executes a HLT instruction
-to halt the processor.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is not implemented.
-
-Board Support Packages
-======================
-
-System Reset
-------------
-
-An RTEMS based application is initiated when the i386 processor is reset.
-When the i386 is reset,
-
-- The EAX register is set to indicate the results of the processorâs
-  power-up self test.  If the self-test was not executed, the contents of
-  this register are undefined.  Otherwise, a non-zero value indicates the
-  processor is faulty and a zero value indicates a successful self-test.
-
-- The DX register holds a component identifier and revision level.  DH
-  contains 3 to indicate an i386 component and DL contains a unique revision
-  level indicator.
-
-- Control register zero (CR0) is set such that the processor is in real
-  mode with paging disabled.  Other portions of CR0 are used to indicate the
-  presence of a numeric coprocessor.
-
-- All bits in the extended flags register (EFLAG) which are not
-  permanently set are cleared.  This inhibits all maskable interrupts.
-
-- The Interrupt Descriptor Register (IDTR) is set to point at address
-  zero.
-
-- All segment registers are set to zero.
-
-- The instruction pointer is set to 0x0000FFF0.  The first instruction
-  executed after a reset is actually at 0xFFFFFFF0 because the i386 asserts
-  the upper twelve address until the first intersegment (FAR) JMP or CALL
-  instruction.  When a JMP or CALL is executed, the upper twelve address
-  lines are lowered and the processor begins executing in the first megabyte
-  of memory.
-
-Typically, an intersegment JMP to the applicationâs initialization code is
-placed at address 0xFFFFFFF0.
-
-Processor Initialization
-------------------------
-
-This initialization code is responsible for initializing all data
-structures required by the i386 in protected mode and for actually entering
-protected mode.  The i386 must be placed in protected mode and the segment
-registers and associated selectors must be initialized before the
-initialize_executive directive is invoked.
-
-The initialization code is responsible for initializing the Global
-Descriptor Table such that the i386 is in the thirty-two bit flat memory
-model with paging disabled.  In this mode, the i386 automatically converts
-every address from a logical to a physical address each time it is used.
-For more information on the memory model used by RTEMS, please refer to the
-Memory Model chapter in this document.
-
-Since the processor is in real mode upon reset, the processor must be
-switched to protected mode before RTEMS can execute.  Before switching to
-protected mode, at least one descriptor table and two descriptors must be
-created.  Descriptors are needed for a code segment and a data segment. (
-This will give you the flat memory model.)  The stack can be placed in a
-normal read/write data segment, so no descriptor for the stack is needed.
-Before the GDT can be used, the base address and limit must be loaded into
-the GDTR register using an LGDT instruction.
-
-If the hardware allows an NMI to be generated, you need to create the IDT
-and a gate for the NMI interrupt handler.  Before the IDT can be used, the
-base address and limit for the idt must be loaded into the IDTR register
-using an LIDT instruction.
-
-Protected mode is entered by setting thye PE bit in the CR0 register.
-Either a LMSW or MOV CR0 instruction may be used to set this bit. Because
-the processor overlaps the interpretation of several instructions, it is
-necessary to discard the instructions from the read-ahead cache. A JMP
-instruction immediately after the LMSW changes the flow and empties the
-processor if intructions which have been pre-fetched and/or decoded.  At
-this point, the processor is in protected mode and begins to perform
-protected mode application initialization.
-
-If the application requires that the IDTR be some value besides zero, then
-it should set it to the required value at this point.  All tasks share the
-same i386 IDTR value.  Because interrupts are enabled automatically by
-RTEMS as part of the initialize_executive directive, the IDTR MUST be set
-properly before this directive is invoked to insure correct interrupt
-vectoring.  If processor caching is to be utilized, then it should be
-enabled during the reset application initialization code.  The reset code
-which is executed before the call to initialize_executive has the following
-requirements:
-
-For more information regarding the i386 data structures and their
-contents, refer to Intelâs 386 Programmerâs Reference Manual.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-.. COMMENT: Jukka Pietarinen <jukka.pietarinen@mrf.fi>, 2008,
-
-.. COMMENT: Micro-Research Finland Oy
-
-Lattice Mico32 Specific Information
-###################################
-
-This chaper discusses the Lattice Mico32 architecture dependencies in
-this port of RTEMS. The Lattice Mico32 is a 32-bit Harvard, RISC
-architecture "soft" microprocessor, available for free with an open IP
-core licensing agreement. Although mainly targeted for Lattice FPGA
-devices the microprocessor can be implemented on other vendorsâ FPGAs,
-too.
-
-**Architecture Documents**
-
-For information on the Lattice Mico32 architecture, refer to the
-following documents available from Lattice Semiconductor:file:`http://www.latticesemi.com/`.
-
-- *"LatticeMico32 Processor Reference Manual"*:file:`http://www.latticesemi.com/dynamic/view_document.cfm?document_id=20890`
-
-CPU Model Dependent Features
-============================
-
-The Lattice Mico32 architecture allows for different configurations of
-the processor. This port is based on the assumption that the following options are implemented:
-
-- hardware multiplier
-
-- hardware divider
-
-- hardware barrel shifter
-
-- sign extension instructions
-
-- instruction cache
-
-- data cache
-
-- debug
-
-Register Architecture
-=====================
-
-This section gives a brief introduction to the register architecture
-of the Lattice Mico32 processor.
-
-The Lattice Mico32 is a RISC archictecture processor with a
-32-register file of 32-bit registers.
-
-Register Name
-
-Function
-
-r0
-
-holds value zero
-
-r1-r25
-
-general purpose
-
-r26/gp
-
-general pupose / global pointer
-
-r27/fp
-
-general pupose / frame pointer
-
-r28/sp
-
-stack pointer
-
-r29/ra
-
-return address
-
-r30/ea
-
-exception address
-
-r31/ba
-
-breakpoint address
-
-Note that on processor startup all register values are undefined
-including r0, thus r0 has to be initialized to zero.
-
-Calling Conventions
-===================
-
-Calling Mechanism
------------------
-
-A call instruction places the return address to register r29 and a
-return from subroutine (ret) is actually a branch to r29/ra.
-
-Register Usage
---------------
-
-A subroutine may freely use registers r1 to r10 which are *not*
-preserved across subroutine invocations.
-
-Parameter Passing
------------------
-
-When calling a C function the first eight arguments are stored in
-registers r1 to r8. Registers r1 and r2 hold the return value.
-
-Memory Model
-============
-
-The Lattice Mico32 processor supports a flat memory model with a 4
-Gbyte address space with 32-bit addresses.
-
-The following data types are supported:
-
-Type
-
-Bits
-
-C Compiler Type
-
-unsigned byte
-
-8
-
-unsigned char
-
-signed byte
-
-8
-
-char
-
-unsigned half-word
-
-16
-
-unsigned short
-
-signed half-word
-
-16
-
-short
-
-unsigned word
-
-32
-
-unsigned int / unsigned long
-
-signed word
-
-32
-
-int / long
-
-Data accesses need to be aligned, with unaligned accesses result are
-undefined.
-
-Interrupt Processing
-====================
-
-The Lattice Mico32 has 32 interrupt lines which are however served by
-only one exception vector. When an interrupt occurs following happens:
-
-- address of next instruction placed in r30/ea
-
-- IE field of IE CSR saved to EIE field and IE field cleared preventing further exceptions from occuring.
-
-- branch to interrupt exception address EBA CSR + 0xC0
-
-The interrupt exception handler determines from the state of the
-interrupt pending registers (IP CSR) and interrupt enable register (IE
-CSR) which interrupt to serve and jumps to the interrupt routine
-pointed to by the corresponding interrupt vector.
-
-For now there is no dedicated interrupt stack so every task in
-the system MUST have enough stack space to accommodate the worst
-case stack usage of that particular task and the interrupt
-service routines COMBINED.
-
-Nested interrupts are not supported.
-
-Default Fatal Error Processing
-==============================
-
-Upon detection of a fatal error by either the application or RTEMS during
-initialization the ``rtems_fatal_error_occurred`` directive supplied
-by the Fatal Error Manager is invoked.  The Fatal Error Manager will
-invoke the user-supplied fatal error handlers.  If no user-supplied
-handlers are configured or all of them return without taking action to
-shutdown the processor or reset, a default fatal error handler is invoked.
-
-Most of the action performed as part of processing the fatal error are
-described in detail in the Fatal Error Manager chapter in the Userâs
-Guide.  However, the if no user provided extension or BSP specific fatal
-error handler takes action, the final default action is to invoke a
-CPU architecture specific function.  Typically this function disables
-interrupts and halts the processor.
-
-In each of the architecture specific chapters, this describes the precise
-operations of the default CPU specific fatal error handler.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is not implemented.
-
-Board Support Packages
-======================
-
-An RTEMS Board Support Package (BSP) must be designed to support a
-particular processor model and target board combination.
-
-In each of the architecture specific chapters, this section will present
-a discussion of architecture specific BSP issues.   For more information
-on developing a BSP, refer to BSP and Device Driver Development Guide
-and the chapter titled Board Support Packages in the RTEMS
-Applications Userâs Guide.
-
-System Reset
-------------
-
-An RTEMS based application is initiated or re-initiated when the processor
-is reset.
-
-.. COMMENT: Copyright (c) 2014 embedded brains GmbH.  All rights reserved.
-
-Renesas M32C Specific Information
-#################################
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is not implemented.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-M68xxx and Coldfire Specific Information
-########################################
-
-This chapter discusses the Freescale (formerly Motorola) MC68xxx
-and Coldfire architectural dependencies.  The MC68xxx family has a
-wide variety of CPU models within it based upon different CPU core
-implementations.  Ignoring the Coldfire parts, the part numbers for
-these models are generally divided into MC680xx and MC683xx.  The MC680xx
-models are more general purpose processors with no integrated peripherals.
-The MC683xx models, on the other hand, are more specialized and have a
-variety of peripherals on chip including sophisticated timers and serial
-communications controllers.
-
-**Architecture Documents**
-
-For information on the MC68xxx and Coldfire architecture, refer to the following documents available from Freescale website (:file:`http//www.freescale.com/`):
-
-- *M68000 Family Reference, Motorola, FR68K/D*.
-
-- *MC68020 Userâs Manual, Motorola, MC68020UM/AD*.
-
-- *MC68881/MC68882 Floating-Point Coprocessor Userâs Manual,
-  Motorola, MC68881UM/AD*.
-
-CPU Model Dependent Features
-============================
-
-This section presents the set of features which vary
-across m68k/Coldfire implementations that are of importance to RTEMS.
-The set of CPU model feature macros are defined in the file``cpukit/score/cpu/m68k/m68k.h`` based upon the particular CPU
-model selected on the compilation command line.
-
-BFFFO Instruction
------------------
-
-The macro ``M68K_HAS_BFFFO`` is set to 1 to indicate that
-this CPU model has the bfffo instruction.
-
-Vector Base Register
---------------------
-
-The macro ``M68K_HAS_VBR`` is set to 1 to indicate that
-this CPU model has a vector base register (vbr).
-
-Separate Stacks
----------------
-
-The macro ``M68K_HAS_SEPARATE_STACKS`` is set to 1 to
-indicate that this CPU model has separate interrupt, user, and
-supervisor mode stacks.
-
-Pre-Indexing Address Mode
--------------------------
-
-The macro ``M68K_HAS_PREINDEXING`` is set to 1 to indicate that
-this CPU model has the pre-indexing address mode.
-
-Extend Byte to Long Instruction
--------------------------------
-
-The macro ``M68K_HAS_EXTB_L`` is set to 1 to indicate that this CPU model
-has the extb.l instruction.  This instruction is supposed to be available
-in all models based on the cpu32 core as well as mc68020 and up models.
-
-Calling Conventions
-===================
-
-The MC68xxx architecture supports a simple yet effective call and
-return mechanism.  A subroutine is invoked via the branch to subroutine
-(``bsr``) or the jump to subroutine (``jsr``) instructions.
-These instructions push the return address on the current stack.
-The return from subroutine (``rts``) instruction pops the return
-address off the current stack and transfers control to that instruction.
-It is is important to note that the MC68xxx call and return mechanism does
-not automatically save or restore any registers.  It is the responsibility
-of the high-level language compiler to define the register preservation
-and usage convention.
-
-Calling Mechanism
------------------
-
-All RTEMS directives are invoked using either a ``bsr`` or ``jsr``
-instruction and return to the user application via the rts instruction.
-
-Register Usage
---------------
-
-As discussed above, the ``bsr`` and ``jsr`` instructions do not
-automatically save any registers.  RTEMS uses the registers D0, D1,
-A0, and A1 as scratch registers.  These registers are not preserved by
-RTEMS directives therefore, the contents of these registers should not
-be assumed upon return from any RTEMS directive.
-
-Parameter Passing
------------------
-
-RTEMS assumes that arguments are placed on the current stack before
-the directive is invoked via the bsr or jsr instruction.  The first
-argument is assumed to be closest to the return address on the stack.
-This means that the first argument of the C calling sequence is pushed
-last.  The following pseudo-code illustrates the typical sequence used
-to call a RTEMS directive with three (3) arguments:
-.. code:: c
-
-    push third argument
-    push second argument
-    push first argument
-    invoke directive
-    remove arguments from the stack
-
-The arguments to RTEMS are typically pushed onto the stack using a move
-instruction with a pre-decremented stack pointer as the destination.
-These arguments must be removed from the stack after control is returned
-to the caller.  This removal is typically accomplished by adding the
-size of the argument list in bytes to the current stack pointer.
-
-Memory Model
-============
-
-The MC68xxx family supports a flat 32-bit address
-space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
-gigabytes).  Each address is represented by a 32-bit value and
-is byte addressable.  The address may be used to reference a
-single byte, word (2-bytes), or long word (4 bytes).  Memory
-accesses within this address space are performed in big endian
-fashion by the processors in this family.
-
-Some of the MC68xxx family members such as the
-MC68020, MC68030, and MC68040 support virtual memory and
-segmentation.  The MC68020 requires external hardware support
-such as the MC68851 Paged Memory Management Unit coprocessor
-which is typically used to perform address translations for
-these systems.  RTEMS does not support virtual memory or
-segmentation on any of the MC68xxx family members.
-
-Interrupt Processing
-====================
-
-Discussed in this section are the MC68xxxâs interrupt response and
-control mechanisms as they pertain to RTEMS.
-
-Vectoring of an Interrupt Handler
----------------------------------
-
-Depending on whether or not the particular CPU supports a separate
-interrupt stack, the MC68xxx family has two different interrupt handling
-models.
-
-Models Without Separate Interrupt Stacks
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Upon receipt of an interrupt the MC68xxx family members without separate
-interrupt stacks automatically perform the following actions:
-
-- To Be Written
-
-Models With Separate Interrupt Stacks
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Upon receipt of an interrupt the MC68xxx family members with separate
-interrupt stacks automatically perform the following actions:
-
-- saves the current status register (SR),
-
-- clears the master/interrupt (M) bit of the SR to
-  indicate the switch from master state to interrupt state,
-
-- sets the privilege mode to supervisor,
-
-- suppresses tracing,
-
-- sets the interrupt mask level equal to the level of the
-  interrupt being serviced,
-
-- pushes an interrupt stack frame (ISF), which includes
-  the program counter (PC), the status register (SR), and the
-  format/exception vector offset (FVO) word, onto the supervisor
-  and interrupt stacks,
-
-- switches the current stack to the interrupt stack and
-  vectors to an interrupt service routine (ISR).  If the ISR was
-  installed with the interrupt_catch directive, then the RTEMS
-  interrupt handler will begin execution.  The RTEMS interrupt
-  handler saves all registers which are not preserved according to
-  the calling conventions and invokes the applicationâs ISR.
-
-A nested interrupt is processed similarly by these
-CPU models with the exception that only a single ISF is placed
-on the interrupt stack and the current stack need not be
-switched.
-
-The FVO word in the Interrupt Stack Frame is examined
-by RTEMS to determine when an outer most interrupt is being
-exited. Since the FVO is used by RTEMS for this purpose, the
-user application code MUST NOT modify this field.
-
-The following shows the Interrupt Stack Frame for
-MC68xxx CPU models with separate interrupt stacks:
-
-+----------------------+-----+
-|    Status Register   | 0x0 |
-+----------------------+-----+
-| Program Counter High | 0x2 |
-+----------------------+-----+
-| Program Counter Low  | 0x4 |
-+----------------------+-----+
-| Format/Vector Offset | 0x6 |
-+----------------------+-----+
-
-
-CPU Models Without VBR and RAM at 0
------------------------------------
-
-This is from a post by Zoltan Kocsi <zoltan@bendor.com.au> and is
-a nice trick in certain situations.  In his words:
-
-I think somebody on this list asked about the interupt vector handling
-w/o VBR and RAM at 0.  The usual trick is to initialise the vector table
-(except the first 2 two entries, of course) to point to the same location
-BUT you also add the vector number times 0x1000000 to them. That is,
-bits 31-24 contain the vector number and 23-0 the address of the common
-handler.  Since the PC is 32 bit wide but the actual address bus is only
-24, the top byte will be in the PC but will be ignored when jumping onto
-your routine.
-
-Then your common interrupt routine gets this info by loading the PC
-into some register and based on that info, you can jump to a vector in
-a vector table pointed by a virtual VBR:
-.. code:: c
-
-    //
-    //  Real vector table at 0
-    //
-    .long   initial_sp
-    .long   initial_pc
-    .long   myhandler+0x02000000
-    .long   myhandler+0x03000000
-    .long   myhandler+0x04000000
-    ...
-    .long   myhandler+0xff000000
-    //
-    // This handler will jump to the interrupt routine   of which
-    // the address is stored at VBR[ vector_no ]
-    // The registers and stackframe will be intact, the interrupt
-    // routine will see exactly what it would see if it was called
-    // directly from the HW vector table at 0.
-    //
-    .comm    VBR,4,2        // This defines the 'virtual' VBR
-    // From C: extern void \*VBR;
-    myhandler:                  // At entry, PC contains the full vector
-    move.l  %d0,-(%sp)      // Save d0
-    move.l  %a0,-(%sp)      // Save a0
-    lea     0(%pc),%a0      // Get the value of the PC
-    move.l  %a0,%d0         // Copy it to a data reg, d0 is VV??????
-    swap    %d0             // Now d0 is ????VV??
-    and.w   #0xff00,%d0     // Now d0 is ????VV00 (1)
-    lsr.w   #6,%d0          // Now d0.w contains the VBR table offset
-    move.l  VBR,%a0         // Get the address from VBR to a0
-    move.l  (%a0,%d0.w),%a0 // Fetch the vector
-    move.l  4(%sp),%d0      // Restore d0
-    move.l  %a0,4(%sp)      // Place target address to the stack
-    move.l  (%sp)+,%a0      // Restore a0, target address is on TOS
-    ret                     // This will jump to the handler and
-    // restore the stack
-    (1) If 'myhandler' is guaranteed to be in the first 64K, e.g. just
-    after the vector table then that insn is not needed.
-
-There are probably shorter ways to do this, but it I believe is enough
-to illustrate the trick. Optimisation is left as an exercise to the
-reader :-)
-
-Interrupt Levels
-----------------
-
-Eight levels (0-7) of interrupt priorities are
-supported by MC68xxx family members with level seven (7) being
-the highest priority.  Level zero (0) indicates that interrupts
-are fully enabled.  Interrupt requests for interrupts with
-priorities less than or equal to the current interrupt mask
-level are ignored.
-
-Although RTEMS supports 256 interrupt levels, the
-MC68xxx family only supports eight.  RTEMS interrupt levels 0
-through 7 directly correspond to MC68xxx interrupt levels.  All
-other RTEMS interrupt levels are undefined and their behavior is
-unpredictable.
-
-Default Fatal Error Processing
-==============================
-
-The default fatal error handler for this architecture disables processor
-interrupts to level 7, places the error code in D0, and executes a``stop`` instruction to simulate a halt processor instruction.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is supported.
-
-Board Support Packages
-======================
-
-System Reset
-------------
-
-An RTEMS based application is initiated or re-initiated when the MC68020
-processor is reset.  When the MC68020 is reset, the processor performs
-the following actions:
-
-- The tracing bits of the status register are cleared to
-  disable tracing.
-
-- The supervisor interrupt state is entered by setting the
-  supervisor (S) bit and clearing the master/interrupt (M) bit of
-  the status register.
-
-- The interrupt mask of the status register is set to
-  level 7 to effectively disable all maskable interrupts.
-
-- The vector base register (VBR) is set to zero.
-
-- The cache control register (CACR) is set to zero to
-  disable and freeze the processor cache.
-
-- The interrupt stack pointer (ISP) is set to the value
-  stored at vector 0 (bytes 0-3) of the exception vector table
-  (EVT).
-
-- The program counter (PC) is set to the value stored at
-  vector 1 (bytes 4-7) of the EVT.
-
-- The processor begins execution at the address stored in
-  the PC.
-
-Processor Initialization
-------------------------
-
-The address of the applicationâs initialization code should be stored in
-the first vector of the EVT which will allow the immediate vectoring to
-the application code.  If the application requires that the VBR be some
-value besides zero, then it should be set to the required value at this
-point.  All tasks share the same MC68020âs VBR value.  Because interrupts
-are enabled automatically by RTEMS as part of the context switch to the
-first task, the VBR MUST be set by either RTEMS of the BSP before this
-occurs ensure correct interrupt vectoring.  If processor caching is
-to be utilized, then it should be enabled during the reset application
-initialization code.
-
-In addition to the requirements described in the
-Board Support Packages chapter of the Applications Userâs
-Manual for the reset code which is executed before the call to
-initialize executive, the MC68020 version has the following
-specific requirements:
-
-- Must leave the S bit of the status register set so that
-  the MC68020 remains in the supervisor state.
-
-- Must set the M bit of the status register to remove the
-  MC68020 from the interrupt state.
-
-- Must set the master stack pointer (MSP) such that a
-  minimum stack size of MINIMUM_STACK_SIZE bytes is provided for
-  the initialize executive directive.
-
-- Must initialize the MC68020âs vector table.
-
-.. COMMENT: Copyright (c) 2014 embedded brains GmbH.  All rights reserved.
-
-Xilinx MicroBlaze Specific Information
-######################################
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is not implemented.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-MIPS Specific Information
-#########################
-
-This chapter discusses the MIPS architecture dependencies
-in this port of RTEMS.  The MIPS family has a wide variety
-of implementations by a wide range of vendors.  Consequently,
-there are many, many CPU models within it.
-
-**Architecture Documents**
-
-IDT docs are online at http://www.idt.com/products/risc/Welcome.html
-
-For information on the XXX architecture, refer to the following documents
-available from VENDOR (:file:`http//www.XXX.com/`):
-
-- *XXX Family Reference, VENDOR, PART NUMBER*.
-
-CPU Model Dependent Features
-============================
-
-This section presents the set of features which vary
-across MIPS implementations and are of importance to RTEMS.
-The set of CPU model feature macros are defined in the file``cpukit/score/cpu/mips/mips.h`` based upon the particular CPU
-model specified on the compilation command line.
-
-Another Optional Feature
-------------------------
-
-The macro XXX
-
-Calling Conventions
-===================
-
-Processor Background
---------------------
-
-TBD
-
-Calling Mechanism
------------------
-
-TBD
-
-Register Usage
---------------
-
-TBD
-
-Parameter Passing
------------------
-
-TBD
-
-Memory Model
-============
-
-Flat Memory Model
------------------
-
-The MIPS family supports a flat 32-bit address
-space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
-gigabytes).  Each address is represented by a 32-bit value and
-is byte addressable.  The address may be used to reference a
-single byte, word (2-bytes), or long word (4 bytes).  Memory
-accesses within this address space are performed in big endian
-fashion by the processors in this family.
-
-Some of the MIPS family members such as the support virtual memory and
-segmentation.  RTEMS does not support virtual memory or
-segmentation on any of these family members.
-
-Interrupt Processing
-====================
-
-Although RTEMS hides many of the processor dependent
-details of interrupt processing, it is important to understand
-how the RTEMS interrupt manager is mapped onto the processorâs
-unique architecture. Discussed in this chapter are the MIPSâs
-interrupt response and control mechanisms as they pertain to
-RTEMS.
-
-Vectoring of an Interrupt Handler
----------------------------------
-
-Upon receipt of an interrupt the XXX family
-members with separate interrupt stacks automatically perform the
-following actions:
-
-- TBD
-
-A nested interrupt is processed similarly by these
-CPU models with the exception that only a single ISF is placed
-on the interrupt stack and the current stack need not be
-switched.
-
-Interrupt Levels
-----------------
-
-TBD
-
-Default Fatal Error Processing
-==============================
-
-The default fatal error handler for this target architecture disables
-processor interrupts, places the error code in *XXX*, and executes a``XXX`` instruction to simulate a halt processor instruction.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is not implemented.
-
-Board Support Packages
-======================
-
-System Reset
-------------
-
-An RTEMS based application is initiated or
-re-initiated when the processor is reset.  When the
-processor is reset, it performs the following actions:
-
-- TBD
-
-Processor Initialization
-------------------------
-
-TBD
-
-.. COMMENT: Copyright (c) 2014 embedded brains GmbH.  All rights reserved.
-
-Altera Nios II Specific Information
-###################################
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is not implemented.
-
-.. COMMENT: COPYRIGHT (c) 2014 Hesham ALMatary <heshamelmatary@gmail.com>
-
-.. COMMENT: All rights reserved.
-
-OpenRISC 1000 Specific Information
-##################################
-
-This chapter discusses the`OpenRISC 1000 architecture <http://opencores.org/or1k/Main_Page>`_
-dependencies in this port of RTEMS. There are many implementations
-for OpenRISC like or1200 and mor1kx. Currently RTEMS supports basic
-features that all implementations should have.
-
-**Architecture Documents**
-
-For information on the OpenRISC 1000 architecture refer to the`OpenRISC 1000 architecture manual <http://openrisc.github.io/or1k.html>`_.
-
-Calling Conventions
-===================
-
-Please refer to the`Function Calling Sequence <http://openrisc.github.io/or1k.html#__RefHeading__504887_595890882>`_.
-
-Floating Point Unit
--------------------
-
-A floating point unit is currently not supported.
-
-Memory Model
-============
-
-A flat 32-bit memory model is supported.
-
-Interrupt Processing
-====================
-
-OpenRISC 1000 architecture has 13 exception types:
-
-- Reset
-
-- Bus Error
-
-- Data Page Fault
-
-- Instruction Page Fault
-
-- Tick Timer
-
-- Alignment
-
-- Illegal Instruction
-
-- External Interrupt
-
-- D-TLB Miss
-
-- I-TLB Miss
-
-- Range
-
-- System Call
-
-- Floating Point
-
-- Trap
-
-Interrupt Levels
-----------------
-
-There are only two levels: interrupts enabled and interrupts disabled.
-
-Interrupt Stack
----------------
-
-The OpenRISC RTEMS port uses a dedicated software interrupt stack.
-The stack for interrupts is allocated during interrupt driver initialization.
-When an  interrupt is entered, the _ISR_Handler routine is responsible for
-switching from the interrupted task stack to RTEMS software interrupt stack.
-
-Default Fatal Error Processing
-==============================
-
-The default fatal error handler for this architecture performs the
-following actions:
-
-- disables operating system supported interrupts (IRQ),
-
-- places the error code in ``r0``, and
-
-- executes an infinite loop to simulate a halt processor instruction.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-.. COMMENT: COPYRIGHT (c) 1989-2007.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-PowerPC Specific Information
-############################
-
-This chapter discusses the PowerPC architecture dependencies
-in this port of RTEMS.  The PowerPC family has a wide variety
-of implementations by a range of vendors.  Consequently,
-there are many, many CPU models within it.
-
-It is highly recommended that the PowerPC RTEMS
-application developer obtain and become familiar with the
-documentation for the processor being used as well as the
-specification for the revision of the PowerPC architecture which
-corresponds to that processor.
-
-**PowerPC Architecture Documents**
-
-For information on the PowerPC architecture, refer to
-the following documents available from Motorola and IBM:
-
-- *PowerPC Microprocessor Family: The Programming Environment*
-  (Motorola Document MPRPPCFPE-01).
-
-- *IBM PPC403GB Embedded Controller Userâs Manual*.
-
-- *PoweRisControl MPC500 Family RCPU RISC Central Processing
-  Unit Reference Manual* (Motorola Document RCPUURM/AD).
-
-- *PowerPC 601 RISC Microprocessor Userâs Manual*
-  (Motorola Document MPR601UM/AD).
-
-- *PowerPC 603 RISC Microprocessor Userâs Manual*
-  (Motorola Document MPR603UM/AD).
-
-- *PowerPC 603e RISC Microprocessor Userâs Manual*
-  (Motorola Document MPR603EUM/AD).
-
-- *PowerPC 604 RISC Microprocessor Userâs Manual*
-  (Motorola Document MPR604UM/AD).
-
-- *PowerPC MPC821 Portable Systems Microprocessor Userâs Manual*
-  (Motorola Document MPC821UM/AD).
-
-- *PowerQUICC MPC860 Userâs Manual* (Motorola Document MPC860UM/AD).
-
-Motorola maintains an on-line electronic library for the PowerPC
-at the following URL:
-
--  http://www.mot.com/powerpc/library/library.html
-
-This site has a a wealth of information and examples.  Many of the
-manuals are available from that site in electronic format.
-
-**PowerPC Processor Simulator Information**
-
-PSIM is a program which emulates the Instruction Set Architecture
-of the PowerPC microprocessor family.  It is reely available in source
-code form under the terms of the GNU General Public License (version
-2 or later).  PSIM can be integrated with the GNU Debugger (gdb) to
-execute and debug PowerPC executables on non-PowerPC hosts.  PSIM
-supports the addition of user provided device models which can be
-used to allow one to develop and debug embedded applications using
-the simulator.
-
-The latest version of PSIM is included in GDB and enabled on pre-built
-binaries provided by the RTEMS Project.
-
-CPU Model Dependent Features
-============================
-
-This section presents the set of features which vary
-across PowerPC implementations and are of importance to RTEMS.
-The set of CPU model feature macros are defined in the file``cpukit/score/cpu/powerpc/powerpc.h`` based upon the particular CPU
-model specified on the compilation command line.
-
-Alignment
----------
-
-The macro PPC_ALIGNMENT is set to the PowerPC modelâs worst case alignment
-requirement for data types on a byte boundary.  This value is used
-to derive the alignment restrictions for memory allocated from
-regions and partitions.
-
-Cache Alignment
----------------
-
-The macro PPC_CACHE_ALIGNMENT is set to the line size of the cache.  It is
-used to align the entry point of critical routines so that as much code
-as possible can be retrieved with the initial read into cache.  This
-is done for the interrupt handler as well as the context switch routines.
-
-In addition, the "shortcut" data structure used by the PowerPC implementation
-to ease access to data elements frequently accessed by RTEMS routines
-implemented in assembly language is aligned using this value.
-
-Maximum Interrupts
-------------------
-
-The macro PPC_INTERRUPT_MAX is set to the number of exception sources
-supported by this PowerPC model.
-
-Has Double Precision Floating Point
------------------------------------
-
-The macro PPC_HAS_DOUBLE is set to 1 to indicate that the PowerPC model
-has support for double precision floating point numbers.  This is
-important because the floating point registers need only be four bytes
-wide (not eight) if double precision is not supported.
-
-Critical Interrupts
--------------------
-
-The macro PPC_HAS_RFCI is set to 1 to indicate that the PowerPC model
-has the Critical Interrupt capability as defined by the IBM 403 models.
-
-Use Multiword Load/Store Instructions
--------------------------------------
-
-The macro PPC_USE_MULTIPLE is set to 1 to indicate that multiword load and
-store instructions should be used to perform context switch operations.
-The relative efficiency of multiword load and store instructions versus
-an equivalent set of single word load and store instructions varies based
-upon the PowerPC model.
-
-Instruction Cache Size
-----------------------
-
-The macro PPC_I_CACHE is set to the size in bytes of the instruction cache.
-
-Data Cache Size
----------------
-
-The macro PPC_D_CACHE is set to the size in bytes of the data cache.
-
-Debug Model
------------
-
-The macro PPC_DEBUG_MODEL is set to indicate the debug support features
-present in this CPU model.  The following debug support feature sets
-are currently supported:
-
-*``PPC_DEBUG_MODEL_STANDARD``*
-    indicates that the single-step trace enable (SE) and branch trace
-    enable (BE) bits in the MSR are supported by this CPU model.
-
-*``PPC_DEBUG_MODEL_SINGLE_STEP_ONLY``*
-    indicates that only the single-step trace enable (SE) bit in the MSR
-    is supported by this CPU model.
-
-*``PPC_DEBUG_MODEL_IBM4xx``*
-    indicates that the debug exception enable (DE) bit in the MSR is supported
-    by this CPU model.  At this time, this particular debug feature set
-    has only been seen in the IBM 4xx series.
-
-Low Power Model
-~~~~~~~~~~~~~~~
-
-The macro PPC_LOW_POWER_MODE is set to indicate the low power model
-supported by this CPU model.  The following low power modes are currently
-supported.
-
-*``PPC_LOW_POWER_MODE_NONE``*
-    indicates that this CPU model has no low power mode support.
-
-*``PPC_LOW_POWER_MODE_STANDARD``*
-    indicates that this CPU model follows the low power model defined for
-    the PPC603e.
-
-Multilibs
-=========
-
-The following multilibs are available:
-
-# ``.``: 32-bit PowerPC with FPU
-
-# ``nof``: 32-bit PowerPC with software floating point support
-
-# ``m403``: Instruction set for PPC403 with FPU
-
-# ``m505``: Instruction set for MPC505 with FPU
-
-# ``m603e``: Instruction set for MPC603e with FPU
-
-# ``m603e/nof``: Instruction set for MPC603e with software floating
-  point support
-
-# ``m604``: Instruction set for MPC604 with FPU
-
-# ``m604/nof``: Instruction set for MPC604 with software floating point
-  support
-
-# ``m860``: Instruction set for MPC860 with FPU
-
-# ``m7400``: Instruction set for MPC7500 with FPU
-
-# ``m7400/nof``: Instruction set for MPC7500 with software floating
-  point support
-
-# ``m8540``: Instruction set for e200, e500 and e500v2 cores with
-  single-precision FPU and SPE
-
-# ``m8540/gprsdouble``: Instruction set for e200, e500 and e500v2 cores
-  with double-precision FPU and SPE
-
-# ``m8540/nof/nospe``: Instruction set for e200, e500 and e500v2 cores
-  with software floating point support and no SPE
-
-# ``me6500/m32``: 32-bit instruction set for e6500 core with FPU and
-  AltiVec
-
-# ``me6500/m32/nof/noaltivec``: 32-bit instruction set for e6500 core
-  with software floating point support and no AltiVec
-
-Calling Conventions
-===================
-
-RTEMS supports the Embedded Application Binary Interface (EABI)
-calling convention.  Documentation for EABI is available by sending
-a message with a subject line of "EABI" to eabi@goth.sis.mot.com.
-
-Programming Model
------------------
-
-This section discusses the programming model for the
-PowerPC architecture.
-
-Non-Floating Point Registers
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-The PowerPC architecture defines thirty-two non-floating point registers
-directly visible to the programmer.  In thirty-two bit implementations, each
-register is thirty-two bits wide.  In sixty-four bit implementations, each
-register is sixty-four bits wide.
-
-These registers are referred to as ``gpr0`` to ``gpr31``.
-
-Some of the registers serve defined roles in the EABI programming model.
-The following table describes the role of each of these registers:
-.. code:: c
-
-    +---------------+----------------+------------------------------+
-    | Register Name | Alternate Name |         Description          |
-    +---------------+----------------+------------------------------+
-    |      r1       |      sp        |         stack pointer        |
-    +---------------+----------------+------------------------------+
-    |               |                |  global pointer to the Small |
-    |      r2       |      na        |     Constant Area (SDA2)     |
-    +---------------+----------------+------------------------------+
-    |    r3 - r12   |      na        | parameter and result passing |
-    +---------------+----------------+------------------------------+
-    |               |                |  global pointer to the Small |
-    |      r13      |      na        |         Data Area (SDA)      |
-    +---------------+----------------+------------------------------+
-
-Floating Point Registers
-~~~~~~~~~~~~~~~~~~~~~~~~
-
-The PowerPC architecture includes thirty-two, sixty-four bit
-floating point registers.  All PowerPC floating point instructions
-interpret these registers as 32 double precision floating point registers,
-regardless of whether the processor has 64-bit or 32-bit implementation.
-
-The floating point status and control register (fpscr) records exceptions
-and the type of result generated by floating-point operations.
-Additionally, it controls the rounding mode of operations and allows the
-reporting of floating exceptions to be enabled or disabled.
-
-Special Registers
-~~~~~~~~~~~~~~~~~
-
-The PowerPC architecture includes a number of special registers
-which are critical to the programming model:
-
-*Machine State Register*
-    The MSR contains the processor mode, power management mode, endian mode,
-    exception information, privilege level, floating point available and
-    floating point excepiton mode, address translation information and
-    the exception prefix.
-
-*Link Register*
-    The LR contains the return address after a function call.  This register
-    must be saved before a subsequent subroutine call can be made.  The
-    use of this register is discussed further in the *Call and Return
-    Mechanism* section below.
-
-*Count Register*
-    The CTR contains the iteration variable for some loops.  It may also be used
-    for indirect function calls and jumps.
-
-Call and Return Mechanism
--------------------------
-
-The PowerPC architecture supports a simple yet effective call
-and return mechanism.  A subroutine is invoked
-via the "branch and link" (``bl``) and
-"brank and link absolute" (``bla``)
-instructions.  This instructions place the return address
-in the Link Register (LR).  The callee returns to the caller by
-executing a "branch unconditional to the link register" (``blr``)
-instruction.  Thus the callee returns to the caller via a jump
-to the return address which is stored in the LR.
-
-The previous contents of the LR are not automatically saved
-by either the ``bl`` or ``bla``.  It is the responsibility
-of the callee to save the contents of the LR before invoking
-another subroutine.  If the callee invokes another subroutine,
-it must restore the LR before executing the ``blr`` instruction
-to return to the caller.
-
-It is important to note that the PowerPC subroutine
-call and return mechanism does not automatically save and
-restore any registers.
-
-The LR may be accessed as special purpose register 8 (``SPR8``) using the
-"move from special register" (``mfspr``) and
-"move to special register" (``mtspr``) instructions.
-
-Calling Mechanism
------------------
-
-All RTEMS directives are invoked using the regular
-PowerPC EABI calling convention via the ``bl`` or``bla`` instructions.
-
-Register Usage
---------------
-
-As discussed above, the call instruction does not
-automatically save any registers.  It is the responsibility
-of the callee to save and restore any registers which must be preserved
-across subroutine calls.  The callee is responsible for saving
-callee-preserved registers to the program stack and restoring them
-before returning to the caller.
-
-Parameter Passing
------------------
-
-RTEMS assumes that arguments are placed in the
-general purpose registers with the first argument in
-register 3 (``r3``), the second argument in general purpose
-register 4 (``r4``), and so forth until the seventh
-argument is in general purpose register 10 (``r10``).
-If there are more than seven arguments, then subsequent arguments
-are placed on the program stack.  The following pseudo-code
-illustrates the typical sequence used to call a RTEMS directive
-with three (3) arguments:
-.. code:: c
-
-    load third argument into r5
-    load second argument into r4
-    load first argument into r3
-    invoke directive
-
-Memory Model
-============
-
-Flat Memory Model
------------------
-
-The PowerPC architecture supports a variety of memory models.
-RTEMS supports the PowerPC using a flat memory model with
-paging disabled.  In this mode, the PowerPC automatically
-converts every address from a logical to a physical address
-each time it is used.  The PowerPC uses information provided
-in the Block Address Translation (BAT) to convert these addresses.
-
-Implementations of the PowerPC architecture may be thirty-two or sixty-four bit.
-The PowerPC architecture supports a flat thirty-two or sixty-four bit address
-space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
-gigabytes) in thirty-two bit implementations or to 0xFFFFFFFFFFFFFFFF
-in sixty-four bit implementations.  Each address is represented
-by either a thirty-two bit or sixty-four bit value and is byte addressable.
-The address may be used to reference a single byte, half-word
-(2-bytes), word (4 bytes), or in sixty-four bit implementations a
-doubleword (8 bytes).  Memory accesses within the address space are
-performed in big or little endian fashion by the PowerPC based
-upon the current setting of the Little-endian mode enable bit (LE)
-in the Machine State Register (MSR).  While the processor is in
-big endian mode, memory accesses which are not properly aligned
-generate an "alignment exception" (vector offset 0x00600).  In
-little endian mode, the PowerPC architecture does not require
-the processor to generate alignment exceptions.
-
-The following table lists the alignment requirements for a variety
-of data accesses:
-
-.. code:: c
-
-    +--------------+-----------------------+
-    |   Data Type  | Alignment Requirement |
-    +--------------+-----------------------+
-    |     byte     |          1            |
-    |   half-word  |          2            |
-    |     word     |          4            |
-    |  doubleword  |          8            |
-    +--------------+-----------------------+
-
-Doubleword load and store operations are only available in
-PowerPC CPU models which are sixty-four bit implementations.
-
-RTEMS does not directly support any PowerPC Memory Management
-Units, therefore, virtual memory or segmentation systems
-involving the PowerPC  are not supported.
-
-.. COMMENT: COPYRIGHT (c) 1989-2007.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Interrupt Processing
-====================
-
-Although RTEMS hides many of the processor dependent
-details of interrupt processing, it is important to understand
-how the RTEMS interrupt manager is mapped onto the processorâs
-unique architecture. Discussed in this chapter are the PowerPCâs
-interrupt response and control mechanisms as they pertain to
-RTEMS.
-
-RTEMS and associated documentation uses the terms interrupt and vector.
-In the PowerPC architecture, these terms correspond to exception and
-exception handler, respectively.  The terms will be used interchangeably
-in this manual.
-
-Synchronous Versus Asynchronous Exceptions
-------------------------------------------
-
-In the PowerPC architecture exceptions can be either precise or
-imprecise and either synchronous or asynchronous.  Asynchronous
-exceptions occur when an external event interrupts the processor.
-Synchronous exceptions are caused by the actions of an
-instruction. During an exception SRR0 is used to calculate where
-instruction processing should resume.  All instructions prior to
-the resume instruction will have completed execution.  SRR1 is used to
-store the machine status.
-
-There are two asynchronous nonmaskable, highest-priority exceptions
-system reset and machine check.  There are two asynchrononous maskable
-low-priority exceptions external interrupt and decrementer.  Nonmaskable
-execptions are never delayed, therefore if two nonmaskable, asynchronous
-exceptions occur in immediate succession, the state information saved by
-the first exception may be overwritten when the subsequent exception occurs.
-
-The PowerPC arcitecure defines one imprecise exception, the imprecise
-floating point enabled exception.  All other synchronous exceptions are
-precise.  The synchronization occuring during asynchronous precise
-exceptions conforms to the requirements for context synchronization.
-
-Vectoring of Interrupt Handler
-------------------------------
-
-Upon determining that an exception can be taken the PowerPC automatically
-performs the following actions:
-
-- an instruction address is loaded into SRR0
-
-- bits 33-36 and 42-47 of SRR1 are loaded with information
-  specific to the exception.
-
-- bits 0-32, 37-41, and 48-63 of SRR1 are loaded with corresponding
-  bits from the MSR.
-
-- the MSR is set based upon the exception type.
-
-- instruction fetch and execution resumes, using the new MSR value, at a location specific to the execption type.
-
-If the interrupt handler was installed as an RTEMS
-interrupt handler, then upon receipt of the interrupt, the
-processor passes control to the RTEMS interrupt handler which
-performs the following actions:
-
-- saves the state of the interrupted task on itâs stack,
-
-- saves all registers which are not normally preserved
-  by the calling sequence so the userâs interrupt service
-  routine can be written in a high-level language.
-
-- if this is the outermost (i.e. non-nested) interrupt,
-  then the RTEMS interrupt handler switches from the current stack
-  to the interrupt stack,
-
-- enables exceptions,
-
-- invokes the vectors to a user interrupt service routine (ISR).
-
-Asynchronous interrupts are ignored while exceptions are
-disabled.  Synchronous interrupts which occur while are
-disabled result in the CPU being forced into an error mode.
-
-A nested interrupt is processed similarly with the
-exception that the current stack need not be switched to the
-interrupt stack.
-
-Interrupt Levels
-----------------
-
-The PowerPC architecture supports only a single external
-asynchronous interrupt source.  This interrupt source
-may be enabled and disabled via the External Interrupt Enable (EE)
-bit in the Machine State Register (MSR).  Thus only two level (enabled
-and disabled) of external device interrupt priorities are
-directly supported by the PowerPC architecture.
-
-Some PowerPC implementations include a Critical Interrupt capability
-which is often used to receive interrupts from high priority external
-devices.
-
-The RTEMS interrupt level mapping scheme for the PowerPC is not
-a numeric level as on most RTEMS ports.  It is a bit mapping in
-which the least three significiant bits of the interrupt level
-are mapped directly to the enabling of specific interrupt
-sources as follows:
-
-*Critical Interrupt*
-    Setting bit 0 (the least significant bit) of the interrupt level
-    enables the Critical Interrupt source, if it is available on this
-    CPU model.
-
-*Machine Check*
-    Setting bit 1 of the interrupt level enables Machine Check execptions.
-
-*External Interrupt*
-    Setting bit 2 of the interrupt level enables External Interrupt execptions.
-
-All other bits in the RTEMS task interrupt level are ignored.
-
-Default Fatal Error Processing
-==============================
-
-The default fatal error handler for this architecture performs the
-following actions:
-
-- places the error code in r3, and
-
-- executes a trap instruction which results in a Program Exception.
-
-If the Program Exception returns, then the following actions are performed:
-
-- disables all processor exceptions by loading a 0 into the MSR, and
-
-- goes into an infinite loop to simulate a halt processor instruction.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is supported.  Available platforms are the Freescale QorIQ P series (e.g.
-P1020) and T series (e.g. T2080, T4240).
-
-Thread-Local Storage
-====================
-
-Thread-local storage is supported.
-
-Board Support Packages
-======================
-
-System Reset
-------------
-
-An RTEMS based application is initiated or
-re-initiated when the PowerPC processor is reset.  The PowerPC
-architecture defines a Reset Exception, but leaves the
-details of the CPU state as implementation specific.  Please
-refer to the Userâs Manual for the CPU model in question.
-
-In general, at power-up the PowerPC begin execution at address
-0xFFF00100 in supervisor mode with all exceptions disabled.  For
-soft resets, the CPU will vector to either 0xFFF00100 or 0x00000100
-depending upon the setting of the Exception Prefix bit in the MSR.
-If during a soft reset, a Machine Check Exception occurs, then the
-CPU may execute a hard reset.
-
-Processor Initialization
-------------------------
-
-If this PowerPC implementation supports on-chip caching
-and this is to be utilized, then it should be enabled during the
-reset application initialization code.  On-chip caching has been
-observed to prevent some emulators from working properly, so it
-may be necessary to run with caching disabled to use these emulators.
-
-In addition to the requirements described in the*Board Support Packages* chapter of the RTEMS C
-Applications Userâs Manual for the reset code
-which is executed before the call to ``rtems_initialize_executive``,
-the PowrePC version has the following specific requirements:
-
-- Must leave the PR bit of the Machine State Register (MSR) set
-  to 0 so the PowerPC remains in the supervisor state.
-
-- Must set stack pointer (sp or r1) such that a minimum stack
-  size of MINIMUM_STACK_SIZE bytes is provided for the RTEMS initialization
-  sequence.
-
-- Must disable all external interrupts (i.e. clear the EI (EE)
-  bit of the machine state register).
-
-- Must enable traps so window overflow and underflow
-  conditions can be properly handled.
-
-- Must initialize the PowerPCâs initial Exception Table with default
-  handlers.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-SuperH Specific Information
-###########################
-
-This chapter discusses the SuperH architecture dependencies
-in this port of RTEMS.  The SuperH family has a wide variety
-of implementations by a wide range of vendors.  Consequently,
-there are many, many CPU models within it.
-
-**Architecture Documents**
-
-For information on the SuperH architecture,
-refer to the following documents available from VENDOR
-(:file:`http//www.XXX.com/`):
-
-- *SuperH Family Reference, VENDOR, PART NUMBER*.
-
-CPU Model Dependent Features
-============================
-
-This chapter presents the set of features which vary
-across SuperH implementations and are of importance to RTEMS.
-The set of CPU model feature macros are defined in the file``cpukit/score/cpu/sh/sh.h`` based upon the particular CPU
-model specified on the compilation command line.
-
-Another Optional Feature
-------------------------
-
-The macro XXX
-
-Calling Conventions
-===================
-
-Calling Mechanism
------------------
-
-All RTEMS directives are invoked using a ``XXX``
-instruction and return to the user application via the``XXX`` instruction.
-
-Register Usage
---------------
-
-The SH1 has 16 general registers (r0..r15).
-
-- r0..r3 used as general volatile registers
-
-- r4..r7 used to pass up to 4 arguments to functions, arguments
-  above 4 are
-  passed via the stack)
-
-- r8..13 caller saved registers (i.e. push them to the stack if you
-  need them inside of a function)
-
-- r14 frame pointer
-
-- r15 stack pointer
-
-Parameter Passing
------------------
-
-XXX
-
-Memory Model
-============
-
-Flat Memory Model
------------------
-
-The SuperH family supports a flat 32-bit address
-space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
-gigabytes).  Each address is represented by a 32-bit value and
-is byte addressable.  The address may be used to reference a
-single byte, word (2-bytes), or long word (4 bytes).  Memory
-accesses within this address space are performed in big endian
-fashion by the processors in this family.
-
-Some of the SuperH family members support virtual memory and
-segmentation.  RTEMS does not support virtual memory or
-segmentation on any of the SuperH family members.  It is the
-responsibility of the BSP to initialize the mapping for
-a flat memory model.
-
-Interrupt Processing
-====================
-
-Although RTEMS hides many of the processor dependent
-details of interrupt processing, it is important to understand
-how the RTEMS interrupt manager is mapped onto the processorâs
-unique architecture. Discussed in this chapter are the MIPSâs
-interrupt response and control mechanisms as they pertain to
-RTEMS.
-
-Vectoring of an Interrupt Handler
----------------------------------
-
-Upon receipt of an interrupt the XXX family
-members with separate interrupt stacks automatically perform the
-following actions:
-
-- TBD
-
-A nested interrupt is processed similarly by these
-CPU models with the exception that only a single ISF is placed
-on the interrupt stack and the current stack need not be
-switched.
-
-Interrupt Levels
-----------------
-
-TBD
-
-Default Fatal Error Processing
-==============================
-
-The default fatal error handler for this architecture disables processor
-interrupts, places the error code in *XXX*, and executes a ``XXX``
-instruction to simulate a halt processor instruction.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is not implemented.
-
-Board Support Packages
-======================
-
-System Reset
-------------
-
-An RTEMS based application is initiated or
-re-initiated when the processor is reset.  When the
-processor is reset, it performs the following actions:
-
-- TBD
-
-Processor Initialization
-------------------------
-
-TBD
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-SPARC Specific Information
-##########################
-
-The Real Time Executive for Multiprocessor Systems
-(RTEMS) is designed to be portable across multiple processor
-architectures.  However, the nature of real-time systems makes
-it essential that the application designer understand certain
-processor dependent implementation details.  These processor
-dependencies include calling convention, board support package
-issues, interrupt processing, exact RTEMS memory requirements,
-performance data, header files, and the assembly language
-interface to the executive.
-
-This document discusses the SPARC architecture dependencies in this
-port of RTEMS.  This architectural port is for SPARC Version 7 and
-8. Implementations for SPARC V9 are in the sparc64 target.
-
-It is highly recommended that the SPARC RTEMS
-application developer obtain and become familiar with the
-documentation for the processor being used as well as the
-specification for the revision of the SPARC architecture which
-corresponds to that processor.
-
-**SPARC Architecture Documents**
-
-For information on the SPARC architecture, refer to
-the following documents available from SPARC International, Inc.
-(http://www.sparc.com):
-
-- SPARC Standard Version 7.
-
-- SPARC Standard Version 8.
-
-**ERC32 Specific Information**
-
-The European Space Agencyâs ERC32 is a three chip
-computing core implementing a SPARC V7 processor and associated
-support circuitry for embedded space applications. The integer
-and floating-point units (90C601E & 90C602E) are based on the
-Cypress 7C601 and 7C602, with additional error-detection and
-recovery functions. The memory controller (MEC) implements
-system support functions such as address decoding, memory
-interface, DMA interface, UARTs, timers, interrupt control,
-write-protection, memory reconfiguration and error-detection.
-The core is designed to work at 25MHz, but using space qualified
-memories limits the system frequency to around 15 MHz, resulting
-in a performance of 10 MIPS and 2 MFLOPS.
-
-Information on the ERC32 and a number of development
-support tools, such as the SPARC Instruction Simulator (SIS),
-are freely available on the Internet.  The following documents
-and SIS are available via anonymous ftp or pointing your web
-browser at ftp://ftp.estec.esa.nl/pub/ws/wsd/erc32.
-
-- ERC32 System Design Document
-
-- MEC Device Specification
-
-Additionally, the SPARC RISC Userâs Guide from Matra
-MHS documents the functionality of the integer and floating
-point units including the instruction set information.  To
-obtain this document as well as ERC32 components and VHDL models
-contact:
-.. code:: c
-
-    Matra MHS SA
-    3 Avenue du Centre, BP 309,
-    78054 St-Quentin-en-Yvelines,
-    Cedex, France
-    VOICE: +31-1-30607087
-    FAX: +31-1-30640693
-
-Amar Guennon (amar.guennon@matramhs.fr) is familiar with the ERC32.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-CPU Model Dependent Features
-============================
-
-Microprocessors are generally classified into
-families with a variety of CPU models or implementations within
-that family.  Within a processor family, there is a high level
-of binary compatibility.  This family may be based on either an
-architectural specification or on maintaining compatibility with
-a popular processor.  Recent microprocessor families such as the
-SPARC or PowerPC are based on an architectural specification
-which is independent or any particular CPU model or
-implementation.  Older families such as the M68xxx and the iX86
-evolved as the manufacturer strived to produce higher
-performance processor models which maintained binary
-compatibility with older models.
-
-RTEMS takes advantage of the similarity of the
-various models within a CPU family.  Although the models do vary
-in significant ways, the high level of compatibility makes it
-possible to share the bulk of the CPU dependent executive code
-across the entire family.
-
-CPU Model Feature Flags
------------------------
-
-Each processor family supported by RTEMS has a
-list of features which vary between CPU models
-within a family.  For example, the most common model dependent
-feature regardless of CPU family is the presence or absence of a
-floating point unit or coprocessor.  When defining the list of
-features present on a particular CPU model, one simply notes
-that floating point hardware is or is not present and defines a
-single constant appropriately.  Conditional compilation is
-utilized to include the appropriate source code for this CPU
-modelâs feature set.  It is important to note that this means
-that RTEMS is thus compiled using the appropriate feature set
-and compilation flags optimal for this CPU model used.  The
-alternative would be to generate a binary which would execute on
-all family members using only the features which were always
-present.
-
-This section presents the set of features which vary
-across SPARC implementations and are of importance to RTEMS.
-The set of CPU model feature macros are defined in the file
-cpukit/score/cpu/sparc/sparc.h based upon the particular CPU
-model defined on the compilation command line.
-
-CPU Model Name
-~~~~~~~~~~~~~~
-
-The macro CPU_MODEL_NAME is a string which designates
-the name of this CPU model.  For example, for the European Space
-Agencyâs ERC32 SPARC model, this macro is set to the string
-"erc32".
-
-Floating Point Unit
-~~~~~~~~~~~~~~~~~~~
-
-The macro SPARC_HAS_FPU is set to 1 to indicate that
-this CPU model has a hardware floating point unit and 0
-otherwise.
-
-Bitscan Instruction
-~~~~~~~~~~~~~~~~~~~
-
-The macro SPARC_HAS_BITSCAN is set to 1 to indicate
-that this CPU model has the bitscan instruction.  For example,
-this instruction is supported by the Fujitsu SPARClite family.
-
-Number of Register Windows
-~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-The macro SPARC_NUMBER_OF_REGISTER_WINDOWS is set to
-indicate the number of register window sets implemented by this
-CPU model.  The SPARC architecture allows a for a maximum of
-thirty-two register window sets although most implementations
-only include eight.
-
-Low Power Mode
-~~~~~~~~~~~~~~
-
-The macro SPARC_HAS_LOW_POWER_MODE is set to one to
-indicate that this CPU model has a low power mode.  If low power
-is enabled, then there must be CPU model specific implementation
-of the IDLE task in cpukit/score/cpu/sparc/cpu.c.  The low
-power mode IDLE task should be of the form:
-.. code:: c
-
-    while ( TRUE ) {
-    enter low power mode
-    }
-
-The code required to enter low power mode is CPU model specific.
-
-CPU Model Implementation Notes
-------------------------------
-
-The ERC32 is a custom SPARC V7 implementation based on the Cypress 601/602
-chipset.  This CPU has a number of on-board peripherals and was developed by
-the European Space Agency to target space applications.  RTEMS currently
-provides support for the following peripherals:
-
-- UART Channels A and B
-
-- General Purpose Timer
-
-- Real Time Clock
-
-- Watchdog Timer (so it can be disabled)
-
-- Control Register (so powerdown mode can be enabled)
-
-- Memory Control Register
-
-- Interrupt Control
-
-The General Purpose Timer and Real Time Clock Timer provided with the ERC32
-share the Timer Control Register.  Because the Timer Control Register is write
-only, we must mirror it in software and insure that writes to one timer do not
-alter the current settings and status of the other timer.  Routines are
-provided in erc32.h which promote the view that the two timers are completely
-independent.  By exclusively using these routines to access the Timer Control
-Register, the application can view the system as having a General Purpose
-Timer Control Register and a Real Time Clock Timer Control Register
-rather than the single shared value.
-
-The RTEMS Idle thread take advantage of the low power mode provided by the
-ERC32.  Low power mode is entered during idle loops and is enabled at
-initialization time.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Calling Conventions
-===================
-
-Each high-level language compiler generates subroutine entry and exit code
-based upon a set of rules known as the application binary interface (ABI)
-calling convention.   These rules address the following issues:
-
-- register preservation and usage
-
-- parameter passing
-
-- call and return mechanism
-
-An ABI calling convention is of importance when interfacing to subroutines
-written in another language either assembly or high-level.  It determines also
-the set of registers to be saved or restored during a context switch and
-interrupt processing.
-
-The ABI relevant for RTEMS on SPARC is defined by SYSTEM V APPLICATION BINARY
-INTERFACE, SPARC Processor Supplement, Third Edition.
-
-Programming Model
------------------
-
-This section discusses the programming model for the
-SPARC architecture.
-
-Non-Floating Point Registers
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-The SPARC architecture defines thirty-two
-non-floating point registers directly visible to the programmer.
-These are divided into four sets:
-
-- input registers
-
-- local registers
-
-- output registers
-
-- global registers
-
-Each register is referred to by either two or three
-names in the SPARC reference manuals.  First, the registers are
-referred to as r0 through r31 or with the alternate notation
-r[0] through r[31].  Second, each register is a member of one of
-the four sets listed above.  Finally, some registers have an
-architecturally defined role in the programming model which
-provides an alternate name.  The following table describes the
-mapping between the 32 registers and the register sets:
-
-.. code:: c
-
-    +-----------------+----------------+------------------+
-    | Register Number | Register Names |   Description    |
-    +-----------------+----------------+------------------+
-    |     0 - 7       |    g0 - g7     | Global Registers |
-    +-----------------+----------------+------------------+
-    |     8 - 15      |    o0 - o7     | Output Registers |
-    +-----------------+----------------+------------------+
-    |    16 - 23      |    l0 - l7     | Local Registers  |
-    +-----------------+----------------+------------------+
-    |    24 - 31      |    i0 - i7     | Input Registers  |
-    +-----------------+----------------+------------------+
-
-As mentioned above, some of the registers serve
-defined roles in the programming model.  The following table
-describes the role of each of these registers:
-
-.. code:: c
-
-    +---------------+----------------+----------------------+
-    | Register Name | Alternate Name |      Description     |
-    +---------------+----------------+----------------------+
-    |     g0        |      na        |    reads return 0    |
-    |               |                |  writes are ignored  |
-    +---------------+----------------+----------------------+
-    |     o6        |      sp        |     stack pointer    |
-    +---------------+----------------+----------------------+
-    |     i6        |      fp        |     frame pointer    |
-    +---------------+----------------+----------------------+
-    |     i7        |      na        |    return address    |
-    +---------------+----------------+----------------------+
-
-The registers g2 through g4 are reserved for applications.  GCC uses them as
-volatile registers by default.  So they are treated like volatile registers in
-RTEMS as well.
-
-The register g6 is reserved for the operating system and contains the address
-of the per-CPU control block of the current processor.  This register is
-initialized during system start and then remains unchanged.  It is not
-saved/restored by the context switch or interrupt processing code.
-
-The register g7 is reserved for the operating system and contains the thread
-pointer used for thread-local storage (TLS) as mandated by the SPARC ABI.
-
-Floating Point Registers
-~~~~~~~~~~~~~~~~~~~~~~~~
-
-The SPARC V7 architecture includes thirty-two,
-thirty-two bit registers.  These registers may be viewed as
-follows:
-
-- 32 single precision floating point or integer registers
-  (f0, f1,  ... f31)
-
-- 16 double precision floating point registers (f0, f2,
-  f4, ... f30)
-
-- 8 extended precision floating point registers (f0, f4,
-  f8, ... f28)
-
-The floating point status register (FSR) specifies
-the behavior of the floating point unit for rounding, contains
-its condition codes, version specification, and trap information.
-
-According to the ABI all floating point registers and the floating point status
-register (FSR) are volatile.  Thus the floating point context of a thread is the
-empty set.  The rounding direction is a system global state and must not be
-modified by threads.
-
-A queue of the floating point instructions which have
-started execution but not yet completed is maintained.  This
-queue is needed to support the multiple cycle nature of floating
-point operations and to aid floating point exception trap
-handlers.  Once a floating point exception has been encountered,
-the queue is frozen until it is emptied by the trap handler.
-The floating point queue is loaded by launching instructions.
-It is emptied normally when the floating point completes all
-outstanding instructions and by floating point exception
-handlers with the store double floating point queue (stdfq)
-instruction.
-
-Special Registers
-~~~~~~~~~~~~~~~~~
-
-The SPARC architecture includes two special registers
-which are critical to the programming model: the Processor State
-Register (psr) and the Window Invalid Mask (wim).  The psr
-contains the condition codes, processor interrupt level, trap
-enable bit, supervisor mode and previous supervisor mode bits,
-version information, floating point unit and coprocessor enable
-bits, and the current window pointer (cwp).  The cwp field of
-the psr and wim register are used to manage the register windows
-in the SPARC architecture.  The register windows are discussed
-in more detail below.
-
-Register Windows
-----------------
-
-The SPARC architecture includes the concept of
-register windows.  An overly simplistic way to think of these
-windows is to imagine them as being an infinite supply of
-"fresh" register sets available for each subroutine to use.  In
-reality, they are much more complicated.
-
-The save instruction is used to obtain a new register
-window.  This instruction decrements the current window pointer,
-thus providing a new set of registers for use.  This register
-set includes eight fresh local registers for use exclusively by
-this subroutine.  When done with a register set, the restore
-instruction increments the current window pointer and the
-previous register set is once again available.
-
-The two primary issues complicating the use of
-register windows are that (1) the set of register windows is
-finite, and (2) some registers are shared between adjacent
-registers windows.
-
-Because the set of register windows is finite, it is
-possible to execute enough save instructions without
-corresponding restoreâs to consume all of the register windows.
-This is easily accomplished in a high level language because
-each subroutine typically performs a save instruction upon
-entry.  Thus having a subroutine call depth greater than the
-number of register windows will result in a window overflow
-condition.  The window overflow condition generates a trap which
-must be handled in software.  The window overflow trap handler
-is responsible for saving the contents of the oldest register
-window on the program stack.
-
-Similarly, the subroutines will eventually complete
-and begin to perform restoreâs.  If the restore results in the
-need for a register window which has previously been written to
-memory as part of an overflow, then a window underflow condition
-results.  Just like the window overflow, the window underflow
-condition must be handled in software by a trap handler.  The
-window underflow trap handler is responsible for reloading the
-contents of the register window requested by the restore
-instruction from the program stack.
-
-The Window Invalid Mask (wim) and the Current Window
-Pointer (cwp) field in the psr are used in conjunction to manage
-the finite set of register windows and detect the window
-overflow and underflow conditions.  The cwp contains the index
-of the register window currently in use.  The save instruction
-decrements the cwp modulo the number of register windows.
-Similarly, the restore instruction increments the cwp modulo the
-number of register windows.  Each bit in the  wim represents
-represents whether a register window contains valid information.
-The value of 0 indicates the register window is valid and 1
-indicates it is invalid.  When a save instruction causes the cwp
-to point to a register window which is marked as invalid, a
-window overflow condition results.  Conversely, the restore
-instruction may result in a window underflow condition.
-
-Other than the assumption that a register window is
-always available for trap (i.e. interrupt) handlers, the SPARC
-architecture places no limits on the number of register windows
-simultaneously marked as invalid (i.e. number of bits set in the
-wim).  However, RTEMS assumes that only one register window is
-marked invalid at a time (i.e. only one bit set in the wim).
-This makes the maximum possible number of register windows
-available to the user while still meeting the requirement that
-window overflow and underflow conditions can be detected.
-
-The window overflow and window underflow trap
-handlers are a critical part of the run-time environment for a
-SPARC application.  The SPARC architectural specification allows
-for the number of register windows to be any power of two less
-than or equal to 32.  The most common choice for SPARC
-implementations appears to be 8 register windows.  This results
-in the cwp ranging in value from 0 to 7 on most implementations.
-
-The second complicating factor is the sharing of
-registers between adjacent register windows.  While each
-register window has its own set of local registers, the input
-and output registers are shared between adjacent windows.  The
-output registers for register window N are the same as the input
-registers for register window ((N - 1) modulo RW) where RW is
-the number of register windows.  An alternative way to think of
-this is to remember how parameters are passed to a subroutine on
-the SPARC.  The caller loads values into what are its output
-registers.  Then after the callee executes a save instruction,
-those parameters are available in its input registers.  This is
-a very efficient way to pass parameters as no data is actually
-moved by the save or restore instructions.
-
-Call and Return Mechanism
--------------------------
-
-The SPARC architecture supports a simple yet
-effective call and return mechanism.  A subroutine is invoked
-via the call (call) instruction.  This instruction places the
-return address in the callerâs output register 7 (o7).  After
-the callee executes a save instruction, this value is available
-in input register 7 (i7) until the corresponding restore
-instruction is executed.
-
-The callee returns to the caller via a jmp to the
-return address.  There is a delay slot following this
-instruction which is commonly used to execute a restore
-instruction â if a register window was allocated by this
-subroutine.
-
-It is important to note that the SPARC subroutine
-call and return mechanism does not automatically save and
-restore any registers.  This is accomplished via the save and
-restore instructions which manage the set of registers windows.
-
-In case a floating-point unit is supported, then floating-point return values
-appear in the floating-point registers.  Single-precision values occupy %f0;
-double-precision values occupy %f0 and %f1.  Otherwise, these are scratch
-registers.  Due to this the hardware and software floating-point ABIs are
-incompatible.
-
-Calling Mechanism
------------------
-
-All RTEMS directives are invoked using the regular
-SPARC calling convention via the call instruction.
-
-Register Usage
---------------
-
-As discussed above, the call instruction does not
-automatically save any registers.  The save and restore
-instructions are used to allocate and deallocate register
-windows.  When a register window is allocated, the new set of
-local registers are available for the exclusive use of the
-subroutine which allocated this register set.
-
-Parameter Passing
------------------
-
-RTEMS assumes that arguments are placed in the
-callerâs output registers with the first argument in output
-register 0 (o0), the second argument in output register 1 (o1),
-and so forth.  Until the callee executes a save instruction, the
-parameters are still visible in the output registers.  After the
-callee executes a save instruction, the parameters are visible
-in the corresponding input registers.  The following pseudo-code
-illustrates the typical sequence used to call a RTEMS directive
-with three (3) arguments:
-.. code:: c
-
-    load third argument into o2
-    load second argument into o1
-    load first argument into o0
-    invoke directive
-
-User-Provided Routines
-----------------------
-
-All user-provided routines invoked by RTEMS, such as
-user extensions, device drivers, and MPCI routines, must also
-adhere to these calling conventions.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Memory Model
-============
-
-A processor may support any combination of memory
-models ranging from pure physical addressing to complex demand
-paged virtual memory systems.  RTEMS supports a flat memory
-model which ranges contiguously over the processorâs allowable
-address space.  RTEMS does not support segmentation or virtual
-memory of any kind.  The appropriate memory model for RTEMS
-provided by the targeted processor and related characteristics
-of that model are described in this chapter.
-
-Flat Memory Model
------------------
-
-The SPARC architecture supports a flat 32-bit address
-space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
-gigabytes).  Each address is represented by a 32-bit value and
-is byte addressable.  The address may be used to reference a
-single byte, half-word (2-bytes), word (4 bytes), or doubleword
-(8 bytes).  Memory accesses within this address space are
-performed in big endian fashion by the SPARC.  Memory accesses
-which are not properly aligned generate a "memory address not
-aligned" trap (type number 7).  The following table lists the
-alignment requirements for a variety of data accesses:
-
-.. code:: c
-
-    +--------------+-----------------------+
-    |   Data Type  | Alignment Requirement |
-    +--------------+-----------------------+
-    |     byte     |          1            |
-    |   half-word  |          2            |
-    |     word     |          4            |
-    |  doubleword  |          8            |
-    +--------------+-----------------------+
-
-Doubleword load and store operations must use a pair
-of registers as their source or destination.  This pair of
-registers must be an adjacent pair of registers with the first
-of the pair being even numbered.  For example, a valid
-destination for a doubleword load might be input registers 0 and
-1 (i0 and i1).  The pair i1 and i2 would be invalid.  \[NOTE:
-Some assemblers for the SPARC do not generate an error if an odd
-numbered register is specified as the beginning register of the
-pair.  In this case, the assembler assumes that what the
-programmer meant was to use the even-odd pair which ends at the
-specified register.  This may or may not have been a correct
-assumption.]
-
-RTEMS does not support any SPARC Memory Management
-Units, therefore, virtual memory or segmentation systems
-involving the SPARC are not supported.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Interrupt Processing
-====================
-
-Different types of processors respond to the
-occurrence of an interrupt in its own unique fashion. In
-addition, each processor type provides a control mechanism to
-allow for the proper handling of an interrupt.  The processor
-dependent response to the interrupt modifies the current
-execution state and results in a change in the execution stream.
-Most processors require that an interrupt handler utilize some
-special control mechanisms to return to the normal processing
-stream.  Although RTEMS hides many of the processor dependent
-details of interrupt processing, it is important to understand
-how the RTEMS interrupt manager is mapped onto the processorâs
-unique architecture. Discussed in this chapter are the SPARCâs
-interrupt response and control mechanisms as they pertain to
-RTEMS.
-
-RTEMS and associated documentation uses the terms
-interrupt and vector.  In the SPARC architecture, these terms
-correspond to traps and trap type, respectively.  The terms will
-be used interchangeably in this manual.
-
-Synchronous Versus Asynchronous Traps
--------------------------------------
-
-The SPARC architecture includes two classes of traps:
-synchronous and asynchronous.  Asynchronous traps occur when an
-external event interrupts the processor.  These traps are not
-associated with any instruction executed by the processor and
-logically occur between instructions.  The instruction currently
-in the execute stage of the processor is allowed to complete
-although subsequent instructions are annulled.  The return
-address reported by the processor for asynchronous traps is the
-pair of instructions following the current instruction.
-
-Synchronous traps are caused by the actions of an
-instruction.  The trap stimulus in this case either occurs
-internally to the processor or is from an external signal that
-was provoked by the instruction.  These traps are taken
-immediately and the instruction that caused the trap is aborted
-before any state changes occur in the processor itself.   The
-return address reported by the processor for synchronous traps
-is the instruction which caused the trap and the following
-instruction.
-
-Vectoring of Interrupt Handler
-------------------------------
-
-Upon receipt of an interrupt the SPARC automatically
-performs the following actions:
-
-- disables traps (sets the ET bit of the psr to 0),
-
-- the S bit of the psr is copied into the Previous
-  Supervisor Mode (PS) bit of the psr,
-
-- the cwp is decremented by one (modulo the number of
-  register windows) to activate a trap window,
-
-- the PC and nPC are loaded into local register 1 and 2
-  (l0 and l1),
-
-- the trap type (tt) field of the Trap Base Register (TBR)
-  is set to the appropriate value, and
-
-- if the trap is not a reset, then the PC is written with
-  the contents of the TBR and the nPC is written with TBR + 4.  If
-  the trap is a reset, then the PC is set to zero and the nPC is
-  set to 4.
-
-Trap processing on the SPARC has two features which
-are noticeably different than interrupt processing on other
-architectures.  First, the value of psr register in effect
-immediately before the trap occurred is not explicitly saved.
-Instead only reversible alterations are made to it.  Second, the
-Processor Interrupt Level (pil) is not set to correspond to that
-of the interrupt being processed.  When a trap occurs, ALL
-subsequent traps are disabled.  In order to safely invoke a
-subroutine during trap handling, traps must be enabled to allow
-for the possibility of register window overflow and underflow
-traps.
-
-If the interrupt handler was installed as an RTEMS
-interrupt handler, then upon receipt of the interrupt, the
-processor passes control to the RTEMS interrupt handler which
-performs the following actions:
-
-- saves the state of the interrupted task on itâs stack,
-
-- insures that a register window is available for
-  subsequent traps,
-
-- if this is the outermost (i.e. non-nested) interrupt,
-  then the RTEMS interrupt handler switches from the current stack
-  to the interrupt stack,
-
-- enables traps,
-
-- invokes the vectors to a user interrupt service routine (ISR).
-
-Asynchronous interrupts are ignored while traps are
-disabled.  Synchronous traps which occur while traps are
-disabled result in the CPU being forced into an error mode.
-
-A nested interrupt is processed similarly with the
-exception that the current stack need not be switched to the
-interrupt stack.
-
-Traps and Register Windows
---------------------------
-
-One of the register windows must be reserved at all
-times for trap processing.  This is critical to the proper
-operation of the trap mechanism in the SPARC architecture.  It
-is the responsibility of the trap handler to insure that there
-is a register window available for a subsequent trap before
-re-enabling traps.  It is likely that any high level language
-routines invoked by the trap handler (such as a user-provided
-RTEMS interrupt handler) will allocate a new register window.
-The save operation could result in a window overflow trap.  This
-trap cannot be correctly processed unless (1) traps are enabled
-and (2) a register window is reserved for traps.  Thus, the
-RTEMS interrupt handler insures that a register window is
-available for subsequent traps before enabling traps and
-invoking the userâs interrupt handler.
-
-Interrupt Levels
-----------------
-
-Sixteen levels (0-15) of interrupt priorities are
-supported by the SPARC architecture with level fifteen (15)
-being the highest priority.  Level zero (0) indicates that
-interrupts are fully enabled.  Interrupt requests for interrupts
-with priorities less than or equal to the current interrupt mask
-level are ignored. Level fifteen (15) is a non-maskable interrupt
-(NMI), which makes it unsuitable for standard usage since it can
-affect the real-time behaviour by interrupting critical sections
-and spinlocks. Disabling traps stops also the NMI interrupt from
-happening. It can however be used for power-down or other
-critical events.
-
-Although RTEMS supports 256 interrupt levels, the
-SPARC only supports sixteen.  RTEMS interrupt levels 0 through
-15 directly correspond to SPARC processor interrupt levels.  All
-other RTEMS interrupt levels are undefined and their behavior is
-unpredictable.
-
-Many LEON SPARC v7/v8 systems features an extended interrupt controller
-which adds an extra step of interrupt decoding to allow handling of
-interrupt 16-31. When such an extended interrupt is generated the CPU
-traps into a specific interrupt trap level 1-14 and software reads out from
-the interrupt controller which extended interrupt source actually caused the
-interrupt.
-
-Disabling of Interrupts by RTEMS
---------------------------------
-
-During the execution of directive calls, critical
-sections of code may be executed.  When these sections are
-encountered, RTEMS disables interrupts to level fifteen (15)
-before the execution of the section and restores them to the
-previous level upon completion of the section.  RTEMS has been
-optimized to ensure that interrupts are disabled for less than
-RTEMS_MAXIMUM_DISABLE_PERIOD microseconds on a RTEMS_MAXIMUM_DISABLE_PERIOD_MHZ
-Mhz ERC32 with zero wait states.
-These numbers will vary based the number of wait states and
-processor speed present on the target board.
-\[NOTE:  The maximum period with interrupts disabled is hand calculated.  This
-calculation was last performed for Release
-RTEMS_RELEASE_FOR_MAXIMUM_DISABLE_PERIOD.]
-
-[NOTE: It is thought that the length of time at which
-the processor interrupt level is elevated to fifteen by RTEMS is
-not anywhere near as long as the length of time ALL traps are
-disabled as part of the "flush all register windows" operation.]
-
-Non-maskable interrupts (NMI) cannot be disabled, and
-ISRs which execute at this level MUST NEVER issue RTEMS system
-calls.  If a directive is invoked, unpredictable results may
-occur due to the inability of RTEMS to protect its critical
-sections.  However, ISRs that make no system calls may safely
-execute as non-maskable interrupts.
-
-Interrupts are disabled or enabled by performing a system call
-to the Operating System reserved software traps 9
-(SPARC_SWTRAP_IRQDIS) or 10 (SPARC_SWTRAP_IRQDIS). The trap is
-generated by the software trap (Ticc) instruction or indirectly
-by calling sparc_disable_interrupts() or sparc_enable_interrupts()
-functions. Disabling interrupts return the previous interrupt level
-(on trap entry) in register G1 and sets PSR.PIL to 15 to disable
-all maskable interrupts. The interrupt level can be restored by
-trapping into the enable interrupt handler with G1 containing the
-new interrupt level.
-
-Interrupt Stack
----------------
-
-The SPARC architecture does not provide for a
-dedicated interrupt stack.  Thus by default, trap handlers would
-execute on the stack of the RTEMS task which they interrupted.
-This artificially inflates the stack requirements for each task
-since EVERY task stack would have to include enough space to
-account for the worst case interrupt stack requirements in
-addition to itâs own worst case usage.  RTEMS addresses this
-problem on the SPARC by providing a dedicated interrupt stack
-managed by software.
-
-During system initialization, RTEMS allocates the
-interrupt stack from the Workspace Area.  The amount of memory
-allocated for the interrupt stack is determined by the
-interrupt_stack_size field in the CPU Configuration Table.  As
-part of processing a non-nested interrupt, RTEMS will switch to
-the interrupt stack before invoking the installed handler.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Default Fatal Error Processing
-==============================
-
-Upon detection of a fatal error by either the
-application or RTEMS the fatal error manager is invoked.  The
-fatal error manager will invoke the user-supplied fatal error
-handlers.  If no user-supplied handlers are configured,  the
-RTEMS provided default fatal error handler is invoked.  If the
-user-supplied fatal error handlers return to the executive the
-default fatal error handler is then invoked.  This chapter
-describes the precise operations of the default fatal error
-handler.
-
-Default Fatal Error Handler Operations
---------------------------------------
-
-The default fatal error handler which is invoked by
-the fatal_error_occurred directive when there is no user handler
-configured or the user handler returns control to RTEMS.
-
-If the BSP has been configured with ``BSP_POWER_DOWN_AT_FATAL_HALT``
-set to true, the default handler will disable interrupts
-and enter power down mode. If power down mode is not available,
-it goes into an infinite loop to simulate a halt processor instruction.
-
-If ``BSP_POWER_DOWN_AT_FATAL_HALT`` is set to false, the default
-handler will place the value ``1`` in register ``g1``, the
-error source in register ``g2``, and the error code in register``g3``. It will then generate a system error which will
-hand over control to the debugger, simulator, etc.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is supported.  Available platforms are the Cobham Gaisler GR712RC and
-GR740.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is supported.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Board Support Packages
-======================
-
-An RTEMS Board Support Package (BSP) must be designed
-to support a particular processor and target board combination.
-This chapter presents a discussion of SPARC specific BSP issues.
-For more information on developing a BSP, refer to the chapter
-titled Board Support Packages in the RTEMS
-Applications Userâs Guide.
-
-System Reset
-------------
-
-An RTEMS based application is initiated or
-re-initiated when the SPARC processor is reset.  When the SPARC
-is reset, the processor performs the following actions:
-
-- the enable trap (ET) of the psr is set to 0 to disable
-  traps,
-
-- the supervisor bit (S) of the psr is set to 1 to enter
-  supervisor mode, and
-
-- the PC is set 0 and the nPC is set to 4.
-
-The processor then begins to execute the code at
-location 0.  It is important to note that all fields in the psr
-are not explicitly set by the above steps and all other
-registers retain their value from the previous execution mode.
-This is true even of the Trap Base Register (TBR) whose contents
-reflect the last trap which occurred before the reset.
-
-Processor Initialization
-------------------------
-
-It is the responsibility of the applicationâs
-initialization code to initialize the TBR and install trap
-handlers for at least the register window overflow and register
-window underflow conditions.  Traps should be enabled before
-invoking any subroutines to allow for register window
-management.  However, interrupts should be disabled by setting
-the Processor Interrupt Level (pil) field of the psr to 15.
-RTEMS installs itâs own Trap Table as part of initialization
-which is initialized with the contents of the Trap Table in
-place when the ``rtems_initialize_executive`` directive was invoked.
-Upon completion of executive initialization, interrupts are
-enabled.
-
-If this SPARC implementation supports on-chip caching
-and this is to be utilized, then it should be enabled during the
-reset application initialization code.
-
-In addition to the requirements described in the
-Board Support Packages chapter of the C
-Applications Users Manual for the reset code
-which is executed before the call to``rtems_initialize_executive``, the SPARC version has the following
-specific requirements:
-
-- Must leave the S bit of the status register set so that
-  the SPARC remains in the supervisor state.
-
-- Must set stack pointer (sp) such that a minimum stack
-  size of MINIMUM_STACK_SIZE bytes is provided for the``rtems_initialize_executive`` directive.
-
-- Must disable all external interrupts (i.e. set the pil
-  to 15).
-
-- Must enable traps so window overflow and underflow
-  conditions can be properly handled.
-
-- Must initialize the SPARCâs initial trap table with at
-  least trap handlers for register window overflow and register
-  window underflow.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-SPARC-64 Specific Information
-#############################
-
-This document discusses the SPARC Version 9 (aka SPARC-64, SPARC64 or SPARC V9)
-architecture dependencies in this port of RTEMS.
-
-The SPARC V9 architecture leaves a lot of undefined implemenation dependencies
-which are defined by the processor models. Consult the specific CPU model
-section in this document for additional documents covering the implementation
-dependent architectural features.
-
-**sun4u Specific Information**
-
-sun4u is the subset of the SPARC V9 implementations comprising the UltraSPARC I
-through UltraSPARC IV processors.
-
-The following documents were used in developing the SPARC-64 sun4u port:
-
-- UltraSPARC  UserÃ¢ÂÂs Manual
-  (http://www.sun.com/microelectronics/manuals/ultrasparc/802-7220-02.pdf)
-
-- UltraSPARC IIIi Processor (datasheets.chipdb.org/Sun/UltraSparc-IIIi.pdf)
-
-**sun4v Specific Information**
-
-sun4v is the subset of the SPARC V9 implementations comprising the
-UltraSPARC T1 or T2 processors.
-
-The following documents were used in developing the SPARC-64 sun4v port:
-
-- UltraSPARC Architecture 2005 Specification
-  (http://opensparc-t1.sunsource.net/specs/UA2005-current-draft-P-EXT.pdf)
-
-- UltraSPARC T1 supplement to UltraSPARC Architecture 2005 Specification
-  (http://opensparc-t1.sunsource.net/specs/UST1-UASuppl-current-draft-P-EXT.pdf)
-
-The defining feature that separates the sun4v architecture from its
-predecessor is the existence of a super-privileged hypervisor that
-is responsible for providing virtualized execution environments.  The impact
-of the hypervisor on the real-time guarantees available with sun4v has not
-yet been determined.
-
-CPU Model Dependent Features
-============================
-
-CPU Model Feature Flags
------------------------
-
-This section presents the set of features which vary across
-SPARC-64 implementations and
-are of importance to RTEMS. The set of CPU model feature macros
-are defined in the file
-cpukit/score/cpu/sparc64/sparc64.h based upon the particular
-CPU model defined on the compilation command line.
-
-CPU Model Name
-~~~~~~~~~~~~~~
-
-The macro CPU MODEL NAME is a string which designates
-the name of this CPU model.
-For example, for the UltraSPARC T1 SPARC V9 model,
-this macro is set to the string "sun4v".
-
-Floating Point Unit
-~~~~~~~~~~~~~~~~~~~
-
-The macro SPARC_HAS_FPU is set to 1 to indicate that
-this CPU model has a hardware floating point unit and 0
-otherwise.
-
-Number of Register Windows
-~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-The macro SPARC_NUMBER_OF_REGISTER_WINDOWS is set to
-indicate the number of register window sets implemented by this
-CPU model.  The SPARC architecture allows for a maximum of
-thirty-two register window sets although most implementations
-only include eight.
-
-CPU Model Implementation Notes
-------------------------------
-
-This section describes the implemenation dependencies of the
-CPU Models sun4u and sun4v of the SPARC V9 architecture.
-
-sun4u Notes
-~~~~~~~~~~~
-
-XXX
-
-sun4v Notes
------------
-
-XXX
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Calling Conventions
-===================
-
-Each high-level language compiler generates
-subroutine entry and exit code based upon a set of rules known
-as the compilerâs calling convention.   These rules address the
-following issues:
-
-- register preservation and usage
-
-- parameter passing
-
-- call and return mechanism
-
-A compilerâs calling convention is of importance when
-interfacing to subroutines written in another language either
-assembly or high-level.  Even when the high-level language and
-target processor are the same, different compilers may use
-different calling conventions.  As a result, calling conventions
-are both processor and compiler dependent.
-
-The following document also provides some conventions on the
-global register usage in SPARC V9:
-http://developers.sun.com/solaris/articles/sparcv9abi.html
-
-Programming Model
------------------
-
-This section discusses the programming model for the
-SPARC architecture.
-
-Non-Floating Point Registers
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-The SPARC architecture defines thirty-two
-non-floating point registers directly visible to the programmer.
-These are divided into four sets:
-
-- input registers
-
-- local registers
-
-- output registers
-
-- global registers
-
-Each register is referred to by either two or three
-names in the SPARC reference manuals.  First, the registers are
-referred to as r0 through r31 or with the alternate notation
-r[0] through r[31].  Second, each register is a member of one of
-the four sets listed above.  Finally, some registers have an
-architecturally defined role in the programming model which
-provides an alternate name.  The following table describes the
-mapping between the 32 registers and the register sets:
-
-.. code:: c
-
-    +-----------------+----------------+------------------+
-    | Register Number | Register Names |   Description    |
-    +-----------------+----------------+------------------+
-    |     0 - 7       |    g0 - g7     | Global Registers |
-    +-----------------+----------------+------------------+
-    |     8 - 15      |    o0 - o7     | Output Registers |
-    +-----------------+----------------+------------------+
-    |    16 - 23      |    l0 - l7     | Local Registers  |
-    +-----------------+----------------+------------------+
-    |    24 - 31      |    i0 - i7     | Input Registers  |
-    +-----------------+----------------+------------------+
-
-As mentioned above, some of the registers serve
-defined roles in the programming model.  The following table
-describes the role of each of these registers:
-
-.. code:: c
-
-    +---------------+----------------+----------------------+
-    | Register Name | Alternate Name |      Description     |
-    +---------------+----------------+----------------------+
-    |     g0        |      na        |    reads return 0    |
-    |               |                |  writes are ignored  |
-    +---------------+----------------+----------------------+
-    |     o6        |      sp        |     stack pointer    |
-    +---------------+----------------+----------------------+
-    |     i6        |      fp        |     frame pointer    |
-    +---------------+----------------+----------------------+
-    |     i7        |      na        |    return address    |
-    +---------------+----------------+----------------------+
-
-Floating Point Registers
-~~~~~~~~~~~~~~~~~~~~~~~~
-
-The SPARC V9 architecture includes sixty-four,
-thirty-two bit registers.  These registers may be viewed as
-follows:
-
-- 32 32-bit single precision floating point or integer registers
-  (f0, f1,  ... f31)
-
-- 32 64-bit double precision floating point registers (f0, f2,
-  f4, ... f62)
-
-- 16 128-bit extended precision floating point registers (f0, f4,
-  f8, ... f60)
-
-The floating point state register (fsr) specifies
-the behavior of the floating point unit for rounding, contains
-its condition codes, version specification, and trap information.
-
-Special Registers
-~~~~~~~~~~~~~~~~~
-
-The SPARC architecture includes a number of special registers:
-
-*``Ancillary State Registers (ASRs)``*
-    The ancillary state registers (ASRs) are optional state registers that
-    may be privileged or nonprivileged. ASRs 16-31 are implementation-
-    dependent. The SPARC V9 ASRs include: y, ccr, asi, tick, pc, fprs.
-    The sun4u ASRs include: pcr, pic, dcr, gsr, softint set, softint clr,
-    softint, and tick cmpr. The sun4v ASRs include: pcr, pic, gsr, soft-
-    int set, softint clr, softint, tick cmpr, stick, and stick cmpr.
-
-*``Processor State Register (pstate)``*
-    The privileged pstate register contains control fields for the proces-
-    sorÃ¢ÂÂs current state. Its flag fields include the interrupt enable, privi-
-    leged mode, and enable FPU.
-
-*``Processor Interrupt Level (pil)``*
-    The PIL specifies the interrupt level above which interrupts will be
-    accepted.
-
-*``Trap Registers``*
-    The trap handling mechanism of the SPARC V9 includes a number of
-    registers, including: trap program counter (tpc), trap next pc (tnpc),
-    trap state (tstate), trap type (tt), trap base address (tba), and trap
-    level (tl).
-
-*``Alternate Globals``*
-    The AG bit of the pstate register provides access to an alternate set
-    of global registers. On sun4v, the AG bit is replaced by the global
-    level (gl) register, providing access to at least two and at most eight
-    alternate sets of globals.
-
-*``Register Window registers``*
-    A number of registers assist in register window management.
-    These include the current window pointer (cwp), savable windows
-    (cansave), restorable windows (canrestore), clean windows (clean-
-    win), other windows (otherwin), and window state (wstate).
-
-Register Windows
-----------------
-
-The SPARC architecture includes the concept of
-register windows.  An overly simplistic way to think of these
-windows is to imagine them as being an infinite supply of
-"fresh" register sets available for each subroutine to use.  In
-reality, they are much more complicated.
-
-The save instruction is used to obtain a new register window.
-This instruction increments the current window pointer, thus
-providing a new set of registers for use. This register set
-includes eight fresh local registers for use exclusively by
-this subroutine. When done with a register set, the restore
-instruction decrements the current window pointer and the
-previous register set is once again available.
-
-The two primary issues complicating the use of register windows
-are that (1) the set of register windows is finite, and (2) some
-registers are shared between adjacent registers windows.
-
-Because the set of register windows is finite, it is
-possible to execute enough save instructions without
-corresponding restoreâs to consume all of the register windows.
-This is easily accomplished in a high level language because
-each subroutine typically performs a save instruction upon
-entry.  Thus having a subroutine call depth greater than the
-number of register windows will result in a window overflow
-condition.  The window overflow condition generates a trap which
-must be handled in software.  The window overflow trap handler
-is responsible for saving the contents of the oldest register
-window on the program stack.
-
-Similarly, the subroutines will eventually complete
-and begin to perform restoreâs.  If the restore results in the
-need for a register window which has previously been written to
-memory as part of an overflow, then a window underflow condition
-results.  Just like the window overflow, the window underflow
-condition must be handled in software by a trap handler.  The
-window underflow trap handler is responsible for reloading the
-contents of the register window requested by the restore
-instruction from the program stack.
-
-The cansave, canrestore, otherwin, and cwp are used in conjunction
-to manage the finite set of register windows and detect the window
-overflow and underflow conditions. The first three of these
-registers must satisfy the invariant cansave + canrestore + otherwin =
-nwindow - 2, where nwindow is the number of register windows.
-The cwp contains the index of the register window currently in use.
-RTEMS does not use the cleanwin and otherwin registers.
-
-The save instruction increments the cwp modulo the number of
-register windows, and if cansave is 0 then it also generates a
-window overflow. Similarly, the restore instruction decrements the
-cwp modulo the number of register windows, and if canrestore is 0 then it
-also generates a window underflow.
-
-Unlike with the SPARC model, the SPARC-64 port does not assume that
-a register window is available for a trap. The window overflow
-and underflow conditions are not detected without hardware generating
-the trap. (These conditions can be detected by reading the register window
-registers and doing some simple arithmetic.)
-
-The window overflow and window underflow trap
-handlers are a critical part of the run-time environment for a
-SPARC application.  The SPARC architectural specification allows
-for the number of register windows to be any power of two less
-than or equal to 32.  The most common choice for SPARC
-implementations appears to be 8 register windows.  This results
-in the cwp ranging in value from 0 to 7 on most implementations.
-
-The second complicating factor is the sharing of
-registers between adjacent register windows.  While each
-register window has its own set of local registers, the input
-and output registers are shared between adjacent windows.  The
-output registers for register window N are the same as the input
-registers for register window ((N + 1) modulo RW) where RW is
-the number of register windows.  An alternative way to think of
-this is to remember how parameters are passed to a subroutine on
-the SPARC.  The caller loads values into what are its output
-registers.  Then after the callee executes a save instruction,
-those parameters are available in its input registers.  This is
-a very efficient way to pass parameters as no data is actually
-moved by the save or restore instructions.
-
-Call and Return Mechanism
--------------------------
-
-The SPARC architecture supports a simple yet
-effective call and return mechanism.  A subroutine is invoked
-via the call (call) instruction.  This instruction places the
-return address in the callerâs output register 7 (o7).  After
-the callee executes a save instruction, this value is available
-in input register 7 (i7) until the corresponding restore
-instruction is executed.
-
-The callee returns to the caller via a jmp to the
-return address.  There is a delay slot following this
-instruction which is commonly used to execute a restore
-instruction â if a register window was allocated by this
-subroutine.
-
-It is important to note that the SPARC subroutine
-call and return mechanism does not automatically save and
-restore any registers.  This is accomplished via the save and
-restore instructions which manage the set of registers windows.
-This allows for the compiler to generate leaf-optimized functions
-that utilize the callerÃ¢ÂÂs output registers without using save and restore.
-
-Calling Mechanism
------------------
-
-All RTEMS directives are invoked using the regular
-SPARC calling convention via the call instruction.
-
-Register Usage
---------------
-
-As discussed above, the call instruction does not
-automatically save any registers.  The save and restore
-instructions are used to allocate and deallocate register
-windows.  When a register window is allocated, the new set of
-local registers are available for the exclusive use of the
-subroutine which allocated this register set.
-
-Parameter Passing
------------------
-
-RTEMS assumes that arguments are placed in the
-callerâs output registers with the first argument in output
-register 0 (o0), the second argument in output register 1 (o1),
-and so forth.  Until the callee executes a save instruction, the
-parameters are still visible in the output registers.  After the
-callee executes a save instruction, the parameters are visible
-in the corresponding input registers.  The following pseudo-code
-illustrates the typical sequence used to call a RTEMS directive
-with three (3) arguments:
-.. code:: c
-
-    load third argument into o2
-    load second argument into o1
-    load first argument into o0
-    invoke directive
-
-User-Provided Routines
-----------------------
-
-All user-provided routines invoked by RTEMS, such as
-user extensions, device drivers, and MPCI routines, must also
-adhere to these calling conventions.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Memory Model
-============
-
-A processor may support any combination of memory
-models ranging from pure physical addressing to complex demand
-paged virtual memory systems.  RTEMS supports a flat memory
-model which ranges contiguously over the processorâs allowable
-address space.  RTEMS does not support segmentation or virtual
-memory of any kind.  The appropriate memory model for RTEMS
-provided by the targeted processor and related characteristics
-of that model are described in this chapter.
-
-Flat Memory Model
------------------
-
-The SPARC-64 architecture supports a flat 64-bit address space with
-addresses ranging from 0x0000000000000000 to 0xFFFFFFFFFFFFFFFF.
-Each address is represented by a 64-bit value (and an 8-bit address
-space identifider or ASI) and is byte addressable. The address
-may be used to reference a single byte, half-word (2-bytes),
-word (4 bytes), doubleword (8 bytes), or quad-word (16 bytes).
-Memory accesses within this address space are performed
-in big endian fashion by the SPARC. Memory accesses which are not
-properly aligned generate a "memory address not aligned" trap
-(type number 0x34). The following table lists the alignment
-requirements for a variety of data accesses:
-
-.. code:: c
-
-    +--------------+-----------------------+
-    |   Data Type  | Alignment Requirement |
-    +--------------+-----------------------+
-    |     byte     |          1            |
-    |   half-word  |          2            |
-    |     word     |          4            |
-    |  doubleword  |          8            |
-    |   quadword   |          16           |
-    +--------------+-----------------------+
-
-RTEMS currently does not support any SPARC Memory Management
-Units, therefore, virtual memory or segmentation systems
-involving the SPARC are not supported.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Interrupt Processing
-====================
-
-RTEMS and associated documentation uses the terms
-interrupt and vector.  In the SPARC architecture, these terms
-correspond to traps and trap type, respectively.  The terms will
-be used interchangeably in this manual. Note that in the SPARC manuals,
-interrupts are a subset of the traps that are delivered to software
-interrupt handlers.
-
-Synchronous Versus Asynchronous Traps
--------------------------------------
-
-The SPARC architecture includes two classes of traps:
-synchronous (precise) and asynchronous (deferred).
-Asynchronous traps occur when an
-external event interrupts the processor.  These traps are not
-associated with any instruction executed by the processor and
-logically occur between instructions.  The instruction currently
-in the execute stage of the processor is allowed to complete
-although subsequent instructions are annulled.  The return
-address reported by the processor for asynchronous traps is the
-pair of instructions following the current instruction.
-
-Synchronous traps are caused by the actions of an
-instruction.  The trap stimulus in this case either occurs
-internally to the processor or is from an external signal that
-was provoked by the instruction.  These traps are taken
-immediately and the instruction that caused the trap is aborted
-before any state changes occur in the processor itself.   The
-return address reported by the processor for synchronous traps
-is the instruction which caused the trap and the following
-instruction.
-
-Vectoring of Interrupt Handler
-------------------------------
-
-Upon receipt of an interrupt the SPARC automatically
-performs the following actions:
-
-- The trap level is set. This provides access to a fresh set of
-  privileged trap-state registers used to save the current state,
-  in effect, pushing a frame on the trap stack.
-  TL <- TL + 1
-
-- Existing state is preserved
-  - TSTATE[TL].CCR <- CCR
-  - TSTATE[TL].ASI <- ASI
-  - TSTATE[TL].PSTATE <- PSTATE
-  - TSTATE[TL].CWP <- CWP
-  - TPC[TL] <- PC
-  - TNPC[TL] <- nPC
-
-- The trap type is preserved. TT[TL] <- the trap type
-
-- The PSTATE register is updated to a predefined state
-  - PSTATE.MM is unchanged
-  - PSTATE.RED <- 0
-  - PSTATE.PEF <- 1 if FPU is present, 0 otherwise
-  - PSTATE.AM <- 0 (address masking is turned off)
-  - PSTATE.PRIV <- 1 (the processor enters privileged mode)
-  - PSTATE.IE <- 0 (interrupts are disabled)
-  - PSTATE.AG <- 1 (global regs are replaced with alternate globals)
-  - PSTATE.CLE <- PSTATE.TLE (set endian mode for traps)
-
-- For a register-window trap only, CWP is set to point to the register
-  window that must be accessed by the trap-handler software, that is:
-
-  - If TT[TL] = 0x24 (a clean window trap), then CWP <- CWP + 1.
-  - If (0x80 <= TT[TL] <= 0xBF) (window spill trap), then CWP <- CWP +
-    CANSAVE + 2.
-  - If (0xC0 <= TT[TL] <= 0xFF) (window fill trap), then CWP <- CWP1.
-  - For non-register-window traps, CWP is not changed.
-
-- Control is transferred into the trap table:
-
-  - PC <- TBA<63:15> (TL>0) TT[TL] 0 0000
-  - nPC <- TBA<63:15> (TL>0) TT[TL] 0 0100
-  - where (TL>0) is 0 if TL = 0, and 1 if TL > 0.
-
-In order to safely invoke a subroutine during trap handling, traps must be
-enabled to allow for the possibility of register window overflow and
-underflow traps.
-
-If the interrupt handler was installed as an RTEMS
-interrupt handler, then upon receipt of the interrupt, the
-processor passes control to the RTEMS interrupt handler which
-performs the following actions:
-
-- saves the state of the interrupted task on itâs stack,
-
-- switches the processor to trap level 0,
-
-- if this is the outermost (i.e. non-nested) interrupt,
-  then the RTEMS interrupt handler switches from the current stack
-  to the interrupt stack,
-
-- enables traps,
-
-- invokes the vectors to a user interrupt service routine (ISR).
-
-Asynchronous interrupts are ignored while traps are
-disabled.  Synchronous traps which occur while traps are
-disabled may result in the CPU being forced into an error mode.
-
-A nested interrupt is processed similarly with the
-exception that the current stack need not be switched to the
-interrupt stack.
-
-Traps and Register Windows
---------------------------
-
-XXX
-
-Interrupt Levels
-----------------
-
-Sixteen levels (0-15) of interrupt priorities are
-supported by the SPARC architecture with level fifteen (15)
-being the highest priority.  Level zero (0) indicates that
-interrupts are fully enabled.  Interrupt requests for interrupts
-with priorities less than or equal to the current interrupt mask
-level are ignored.
-
-Although RTEMS supports 256 interrupt levels, the
-SPARC only supports sixteen.  RTEMS interrupt levels 0 through
-15 directly correspond to SPARC processor interrupt levels.  All
-other RTEMS interrupt levels are undefined and their behavior is
-unpredictable.
-
-Disabling of Interrupts by RTEMS
---------------------------------
-
-XXX
-
-Interrupt Stack
----------------
-
-The SPARC architecture does not provide for a
-dedicated interrupt stack.  Thus by default, trap handlers would
-execute on the stack of the RTEMS task which they interrupted.
-This artificially inflates the stack requirements for each task
-since EVERY task stack would have to include enough space to
-account for the worst case interrupt stack requirements in
-addition to itâs own worst case usage.  RTEMS addresses this
-problem on the SPARC by providing a dedicated interrupt stack
-managed by software.
-
-During system initialization, RTEMS allocates the
-interrupt stack from the Workspace Area.  The amount of memory
-allocated for the interrupt stack is determined by the
-interrupt_stack_size field in the CPU Configuration Table.  As
-part of processing a non-nested interrupt, RTEMS will switch to
-the interrupt stack before invoking the installed handler.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Default Fatal Error Processing
-==============================
-
-Upon detection of a fatal error by either the
-application or RTEMS the fatal error manager is invoked.  The
-fatal error manager will invoke the user-supplied fatal error
-handlers.  If no user-supplied handlers are configured,  the
-RTEMS provided default fatal error handler is invoked.  If the
-user-supplied fatal error handlers return to the executive the
-default fatal error handler is then invoked.  This chapter
-describes the precise operations of the default fatal error
-handler.
-
-Default Fatal Error Handler Operations
---------------------------------------
-
-The default fatal error handler which is invoked by
-the fatal_error_occurred directive when there is no user handler
-configured or the user handler returns control to RTEMS.  The
-default fatal error handler disables processor interrupts to
-level 15, places the error code in g1, and goes into an infinite
-loop to simulate a halt processor instruction.
-
-Symmetric Multiprocessing
-=========================
-
-SMP is not supported.
-
-Thread-Local Storage
-====================
-
-Thread-local storage is supported.
-
-.. COMMENT: COPYRIGHT (c) 1988-2002.
-
-.. COMMENT: On-Line Applications Research Corporation (OAR).
-
-.. COMMENT: All rights reserved.
-
-Board Support Packages
-======================
-
-An RTEMS Board Support Package (BSP) must be designed
-to support a particular processor and target board combination.
-This chapter presents a discussion of SPARC specific BSP issues.
-For more information on developing a BSP, refer to the chapter
-titled Board Support Packages in the RTEMS
-Applications Userâs Guide.
-
-HelenOS and Open Firmware
--------------------------
-
-The provided BSPs make use of some bootstrap and low-level hardware code
-of the HelenOS operating system. These files can be found in the shared/helenos
-directory of the sparc64 bsp directory.  Consult the sources for more
-detailed information.
-
-The shared BSP code also uses the Open Firmware interface to re-use firmware
-code, primarily for console support and default trap handlers.
-
-Command and Variable Index
-##########################
-
-There are currently no Command and Variable Index entries.
-
-.. COMMENT: @printindex fn
-
-Concept Index
-#############
-
-There are currently no Concept Index entries.
-
-.. COMMENT: @printindex cp 
Index: cpu_supplement/cpu_supplement_old_reference_only.rst
===================================================================
--- cpu_supplement/cpu_supplement_old_reference_only.rst	(revision 3c29186a503f986a45ad76945119173973f511b1)
+++ cpu_supplement/cpu_supplement_old_reference_only.rst	(revision 3c29186a503f986a45ad76945119173973f511b1)
@@ -0,0 +1,4760 @@
+:orphan:
+
+
+
+.. COMMENT: %**end of header
+
+.. COMMENT: COPYRIGHT (c) 1989-2013.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+.. COMMENT: Master file for the CPU Supplement
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+.. COMMENT: The following determines which set of the tables and figures we will use.
+
+.. COMMENT: We default to ASCII but if available TeX or HTML versions will
+
+.. COMMENT: be used instead.
+
+.. COMMENT: @clear use-html
+
+.. COMMENT: @clear use-tex
+
+.. COMMENT: The following variable says to use texinfo or html for the two column
+
+.. COMMENT: texinfo tables.  For somethings the format does not look good in html.
+
+.. COMMENT: With our adjustment to the left column in TeX, it nearly always looks
+
+.. COMMENT: good printed.
+
+.. COMMENT: Custom whitespace adjustments.  We could fiddle a bit more.
+
+.. COMMENT: Title Page Stuff
+
+.. COMMENT: I don't really like having a short title page.  -joel
+
+.. COMMENT: @shorttitlepage RTEMS CPU Architecture Supplement
+
+=================================
+RTEMS CPU Architecture Supplement
+=================================
+
+.. COMMENT: COPYRIGHT (c) 1988-2015.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+.. COMMENT: The following puts a space somewhere on an otherwise empty page so we
+
+.. COMMENT: can force the copyright description onto a left hand page.
+
+COPYRIGHT Â© 1988 - 2015.
+
+On-Line Applications Research Corporation (OAR).
+
+The authors have used their best efforts in preparing
+this material.  These efforts include the development, research,
+and testing of the theories and programs to determine their
+effectiveness.  No warranty of any kind, expressed or implied,
+with regard to the software or the material contained in this
+document is provided.  No liability arising out of the
+application or use of any product described in this document is
+assumed.  The authors reserve the right to revise this material
+and to make changes from time to time in the content hereof
+without obligation to notify anyone of such revision or changes.
+
+The RTEMS Project is hosted at http://www.rtems.org.  Any
+inquiries concerning RTEMS, its related support components, or its
+documentation should be directed to the Community Project hosted athttp://www.rtems.org.
+
+Any inquiries for commercial services including training, support, custom
+development, application development assistance should be directed tohttp://www.rtems.com.
+
+.. COMMENT: This prevents a black box from being printed on "overflow" lines.
+
+.. COMMENT: The alternative is to rework a sentence to avoid this problem.
+
+RTEMS CPU Architecture Supplement
+#################################
+
+.. COMMENT: COPYRIGHT (c) 1989-2011.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Preface
+#######
+
+The Real Time Executive for Multiprocessor Systems
+(RTEMS) is designed to be portable across multiple processor
+architectures.  However, the nature of real-time systems makes
+it essential that the application designer understand certain
+processor dependent implementation details.  These processor
+dependencies include calling convention, board support package
+issues, interrupt processing, exact RTEMS memory requirements,
+performance data, header files, and the assembly language
+interface to the executive.
+
+Each architecture represents a CPU family and usually there are
+a wide variety of CPU models within it.  These models share a
+common Instruction Set Architecture (ISA) which often varies
+based upon some well-defined rules.  There are often
+multiple implementations of the ISA and these may be from
+one or multiple vendors.
+
+On top of variations in the ISA, there may also be variations
+which occur when a CPU core implementation is combined with
+a set of peripherals to form a system on chip.  For example,
+there are many ARM CPU models from numerous semiconductor
+vendors and a wide variety of peripherals.  But at the
+ISA level, they share a common compatibility.
+
+RTEMS depends upon this core similarity across the CPU models
+and leverages that to minimize the source code that is specific
+to any particular CPU core implementation or CPU model.
+
+This manual is separate and distinct from the RTEMS Porting
+Guide.  That manual is a guide on porting RTEMS to a new
+architecture.  This manual is focused on the more mundane
+CPU architecture specific issues that may impact
+application development.  For example, if you need to write
+a subroutine in assembly language, it is critical to understand
+the calling conventions for the target architecture.
+
+The first chapter in this manual describes these issues
+in general terms.  In a sense, it is posing the questions
+one should be aware may need to be answered and understood
+when porting an RTEMS application to a new architecture.
+Each subsequent chapter gives the answers to those questions
+for a particular CPU architecture.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Port Specific Information
+#########################
+
+This chaper provides a general description of the type of
+architecture specific information which is in each of
+the architecture specific chapters that follow.  The outline
+of this chapter is identical to that of the architecture
+specific chapters.
+
+In each of the architecture specific chapters, this
+introductory section will provide an overview of the
+architecture
+
+**Architecture Documents**
+
+In each of the architecture specific chapters, this
+section will provide pointers on where to obtain
+documentation.
+
+CPU Model Dependent Features
+============================
+
+Microprocessors are generally classified into families with a variety of
+CPU models or implementations within that family.  Within a processor
+family, there is a high level of binary compatibility.  This family
+may be based on either an architectural specification or on maintaining
+compatibility with a popular processor.  Recent microprocessor families
+such as the SPARC or PowerPC are based on an architectural specification
+which is independent or any particular CPU model or implementation.
+Older families such as the Motorola 68000 and the Intel x86 evolved as the
+manufacturer strived to produce higher performance processor models which
+maintained binary compatibility with older models.
+
+RTEMS takes advantage of the similarity of the various models within a
+CPU family.  Although the models do vary in significant ways, the high
+level of compatibility makes it possible to share the bulk of the CPU
+dependent executive code across the entire family.  Each processor family
+supported by RTEMS has a list of features which vary between CPU models
+within a family.  For example, the most common model dependent feature
+regardless of CPU family is the presence or absence of a floating point
+unit or coprocessor.  When defining the list of features present on a
+particular CPU model, one simply notes that floating point hardware
+is or is not present and defines a single constant appropriately.
+Conditional compilation is utilized to include the appropriate source
+code for this CPU modelâs feature set.  It is important to note that
+this means that RTEMS is thus compiled using the appropriate feature set
+and compilation flags optimal for this CPU model used.  The alternative
+would be to generate a binary which would execute on all family members
+using only the features which were always present.
+
+The set of CPU model feature macros are defined in the file``cpukit/score/cpu/CPU/rtems/score/cpu.h`` based upon the GNU tools
+multilib variant that is appropriate for the particular CPU model defined
+on the compilation command line.
+
+In each of the architecture specific chapters, this section presents
+the set of features which vary across various implementations of the
+architecture that may be of importance to RTEMS application developers.
+
+The subsections will vary amongst the target architecture chapters as
+the specific features may vary.  However, each port will include a few
+common features such as the CPU Model Name and presence of a hardware
+Floating Point Unit.  The common features are described here.
+
+CPU Model Name
+--------------
+
+The macro ``CPU_MODEL_NAME`` is a string which designates
+the name of this CPU model.  For example, for the MC68020
+processor model from the m68k architecture, this macro
+is set to the string "mc68020".
+
+Floating Point Unit
+-------------------
+
+In most architectures, the presence of a floating point unit is an option.
+It does not matter whether the hardware floating point support is
+incorporated on-chip or is an external coprocessor as long as it
+appears an FPU per the ISA.  However, if a hardware FPU is not present,
+it is possible that the floating point emulation library for this
+CPU is not reentrant and thus context switched by RTEMS.
+
+RTEMS provides two feature macros to indicate the FPU configuration:
+
+- CPU_HARDWARE_FP
+  is set to TRUE to indicate that a hardware FPU is present.
+
+- CPU_SOFTWARE_FP
+  is set to TRUE to indicate that a hardware FPU is not present and that
+  the FP software emulation will be context switched.
+
+Multilibs
+=========
+
+Newlib and GCC provide several target libraries like the :file:`libc.a`,:file:`libm.a` and :file:`libgcc.a`.  These libraries are artifacts of the GCC
+build process.  Newlib is built together with GCC.  To provide optimal support
+for various chip derivatives and instruction set revisions multiple variants of
+these libraries are available for each architecture.  For example one set may
+use software floating point support and another set may use hardware floating
+point instructions.  These sets of libraries are called *multilibs*.  Each
+library set corresponds to an application binary interface (ABI) and
+instruction set.
+
+A multilib variant can be usually detected via built-in compiler defines at
+compile-time.  This mechanism is used by RTEMS to select for example the
+context switch support for a particular BSP.  The built-in compiler defines
+corresponding to multilibs are the only architecture specific defines allowed
+in the ``cpukit`` area of the RTEMS sources.
+
+Invoking the GCC with the ``-print-multi-lib`` option lists the available
+multilibs.  Each line of the output describes one multilib variant.  The
+default variant is denoted by ``.`` which is selected when no or
+contradicting GCC machine options are selected.  The multilib selection for a
+target is specified by target makefile fragments (see file :file:`t-rtems` in
+the GCC sources and section`The Target Makefile Fragment <https://gcc.gnu.org/onlinedocs/gccint/Target-Fragment.html#Target-Fragment>`_
+in the `GCC Internals Manual <https://gcc.gnu.org/onlinedocs/gccint/>`_.
+
+Calling Conventions
+===================
+
+Each high-level language compiler generates subroutine entry and exit
+code based upon a set of rules known as the compilerâs calling convention.
+These rules address the following issues:
+
+- register preservation and usage
+
+- parameter passing
+
+- call and return mechanism
+
+A compilerâs calling convention is of importance when
+interfacing to subroutines written in another language either
+assembly or high-level.  Even when the high-level language and
+target processor are the same, different compilers may use
+different calling conventions.  As a result, calling conventions
+are both processor and compiler dependent.
+
+Calling Mechanism
+-----------------
+
+In each of the architecture specific chapters, this subsection will
+describe the instruction(s) used to perform a *normal* subroutine
+invocation.  All RTEMS directives are invoked as *normal* C language
+functions so it is important to the user application to understand the
+call and return mechanism.
+
+Register Usage
+--------------
+
+In each of the architecture specific chapters, this subsection will
+detail the set of registers which are *NOT* preserved across subroutine
+invocations.  The registers which are not preserved are assumed to be
+available for use as scratch registers.  Therefore, the contents of these
+registers should not be assumed upon return from any RTEMS directive.
+
+In some architectures, there may be a set of registers made available
+automatically as a side-effect of the subroutine invocation
+mechanism.
+
+Parameter Passing
+-----------------
+
+In each of the architecture specific chapters, this subsection will
+describe the mechanism by which the parameters or arguments are passed
+by the caller to a subroutine.  In some architectures, all parameters
+are passed on the stack while in others some are passed in registers.
+
+User-Provided Routines
+----------------------
+
+All user-provided routines invoked by RTEMS, such as
+user extensions, device drivers, and MPCI routines, must also
+adhere to these calling conventions.
+
+Memory Model
+============
+
+A processor may support any combination of memory
+models ranging from pure physical addressing to complex demand
+paged virtual memory systems.  RTEMS supports a flat memory
+model which ranges contiguously over the processorâs allowable
+address space.  RTEMS does not support segmentation or virtual
+memory of any kind.  The appropriate memory model for RTEMS
+provided by the targeted processor and related characteristics
+of that model are described in this chapter.
+
+Flat Memory Model
+-----------------
+
+Most RTEMS target processors can be initialized to support a flat address
+space.  Although the size of addresses varies between architectures, on
+most RTEMS targets, an address is 32-bits wide which defines addresses
+ranging from 0x00000000 to 0xFFFFFFFF (4 gigabytes).  Each address is
+represented by a 32-bit value and is byte addressable.  The address may be
+used to reference a single byte, word (2-bytes), or long word (4 bytes).
+Memory accesses within this address space may be performed in little or
+big endian fashion.
+
+On smaller CPU architectures supported by RTEMS, the address space
+may only be 20 or 24 bits wide.
+
+If the CPU model has support for virtual memory or segmentation, it is
+the responsibility of the Board Support Package (BSP) to initialize the
+MMU hardware to perform address translations which correspond to flat
+memory model.
+
+In each of the architecture specific chapters, this subsection will
+describe any architecture characteristics that differ from this general
+description.
+
+Interrupt Processing
+====================
+
+Different types of processors respond to the occurrence of an interrupt
+in its own unique fashion. In addition, each processor type provides
+a control mechanism to allow for the proper handling of an interrupt.
+The processor dependent response to the interrupt modifies the current
+execution state and results in a change in the execution stream.  Most
+processors require that an interrupt handler utilize some special control
+mechanisms to return to the normal processing stream.  Although RTEMS
+hides many of the processor dependent details of interrupt processing,
+it is important to understand how the RTEMS interrupt manager is mapped
+onto the processorâs unique architecture.
+
+RTEMS supports a dedicated interrupt stack for all architectures.
+On architectures with hardware support for a dedicated interrupt stack,
+it will be initialized such that when an interrupt occurs, the processor
+automatically switches to this dedicated stack.  On architectures without
+hardware support for a dedicated interrupt stack which is separate from
+those of the tasks, RTEMS will support switching to a dedicated stack
+for interrupt processing.
+
+Without a dedicated interrupt stack, every task in
+the system MUST have enough stack space to accommodate the worst
+case stack usage of that particular task and the interrupt
+service routines COMBINED.  By supporting a dedicated interrupt
+stack, RTEMS significantly lowers the stack requirements for
+each task.
+
+A nested interrupt is processed similarly with the exception that since
+the CPU is already executing on the interrupt stack, there is no need
+to switch to the interrupt stack.
+
+In some configurations, RTEMS allocates the interrupt stack from the
+Workspace Area.  The amount of memory allocated for the interrupt stack
+is user configured and based upon the ``confdefs.h`` parameter``CONFIGURE_INTERRUPT_STACK_SIZE``.  This parameter is described
+in detail in the Configuring a System chapter of the Userâs Guide.
+On configurations in which RTEMS allocates the interrupt stack, during
+the initialization process, RTEMS will also install its interrupt stack.
+In other configurations, the interrupt stack is allocated and installed
+by the Board Support Package (BSP).
+
+In each of the architecture specific chapters, this section discesses
+the interrupt response and control mechanisms of the architecture as
+they pertain to RTEMS.
+
+Vectoring of an Interrupt Handler
+---------------------------------
+
+In each of the architecture specific chapters, this subsection will
+describe the architecture specific details of the interrupt vectoring
+process.  In particular, it should include a description of the
+Interrupt Stack Frame (ISF).
+
+Interrupt Levels
+----------------
+
+In each of the architecture specific chapters, this subsection will
+describe how the interrupt levels available on this particular architecture
+are mapped onto the 255 reserved in the task mode.  The interrupt level
+value of zero (0) should always mean that interrupts are enabled.
+
+Any use of an  interrupt level that is is not undefined on a particular
+architecture may result in behavior that is unpredictable.
+
+Disabling of Interrupts by RTEMS
+--------------------------------
+
+During the execution of directive calls, critical sections of code may
+be executed.  When these sections are encountered, RTEMS disables all
+external interrupts before the execution of this section and restores
+them to the previous level upon completion of the section.  RTEMS has
+been optimized to ensure that interrupts are disabled for the shortest
+number of instructions possible.  Since the precise number of instructions
+and their execution time varies based upon target CPU family, CPU model,
+board memory speed, compiler version, and optimization level, it is
+not practical to provide the precise number for all possible RTEMS
+configurations.
+
+Historically, the measurements were made by hand analyzing and counting
+the execution time of instruction sequences during interrupt disable
+critical sections.  For reference purposes, on a 16 Mhz Motorola
+MC68020, the maximum interrupt disable period was typically approximately
+ten (10) to thirteen (13) microseconds.  This architecture was memory bound
+and had a slow bit scan instruction.  In contrast, during the same
+period a 14 Mhz SPARC would have a worst case disable time of approximately
+two (2) to three (3) microseconds because it had a single cycle bit scan
+instruction and used fewer cycles for memory accesses.
+
+If you are interested in knowing the worst case execution time for
+a particular version of RTEMS, please contact OAR Corporation and
+we will be happy to product the results as a consulting service.
+
+Non-maskable interrupts (NMI) cannot be disabled, and
+ISRs which execute at this level MUST NEVER issue RTEMS system
+calls.  If a directive is invoked, unpredictable results may
+occur due to the inability of RTEMS to protect its critical
+sections.  However, ISRs that make no system calls may safely
+execute as non-maskable interrupts.
+
+Default Fatal Error Processing
+==============================
+
+Upon detection of a fatal error by either the application or RTEMS during
+initialization the ``rtems_fatal_error_occurred`` directive supplied
+by the Fatal Error Manager is invoked.  The Fatal Error Manager will
+invoke the user-supplied fatal error handlers.  If no user-supplied
+handlers are configured or all of them return without taking action to
+shutdown the processor or reset, a default fatal error handler is invoked.
+
+Most of the action performed as part of processing the fatal error are
+described in detail in the Fatal Error Manager chapter in the Userâs
+Guide.  However, the if no user provided extension or BSP specific fatal
+error handler takes action, the final default action is to invoke a
+CPU architecture specific function.  Typically this function disables
+interrupts and halts the processor.
+
+In each of the architecture specific chapters, this describes the precise
+operations of the default CPU specific fatal error handler.
+
+Symmetric Multiprocessing
+=========================
+
+This section contains information about the Symmetric Multiprocessing (SMP)
+status of a particular architecture.
+
+Thread-Local Storage
+====================
+
+In order to support thread-local storage (TLS) the CPU port must implement the
+facilities mandated by the application binary interface (ABI) of the CPU
+architecture.  The CPU port must initialize the TLS area in the``_CPU_Context_Initialize()`` function.  There are support functions available
+via ``#include <rtems/score/tls.h>`` which implement Variants I and II
+according to Ulrich Drepper, *ELF Handling For Thread-Local Storage*.
+
+``_TLS_TCB_at_area_begin_initialize()``
+    Uses Variant I, TLS offsets emitted by linker takes the TCB into account.  For
+    a reference implementation see :file:`cpukit/score/cpu/arm/cpu.c`.
+
+``_TLS_TCB_before_TLS_block_initialize()``
+    Uses Variant I, TLS offsets emitted by linker neglects the TCB.  For a
+    reference implementation see:file:`c/src/lib/libcpu/powerpc/new-exceptions/cpu.c`.
+
+``_TLS_TCB_after_TLS_block_initialize()``
+    Uses Variant II.  For a reference implementation see:file:`cpukit/score/cpu/sparc/cpu.c`.
+
+The board support package (BSP) must provide the following sections and symbols
+in its linker command file:
+.. code:: c
+
+    .tdata : {
+    _TLS_Data_begin = .;
+    \*(.tdata .tdata.* .gnu.linkonce.td.*)
+    _TLS_Data_end = .;
+    }
+    .tbss : {
+    _TLS_BSS_begin = .;
+    \*(.tbss .tbss.* .gnu.linkonce.tb.*) \*(.tcommon)
+    _TLS_BSS_end = .;
+    }
+    _TLS_Data_size = _TLS_Data_end - _TLS_Data_begin;
+    _TLS_Data_begin = _TLS_Data_size != 0 ? _TLS_Data_begin : _TLS_BSS_begin;
+    _TLS_Data_end = _TLS_Data_size != 0 ? _TLS_Data_end : _TLS_BSS_begin;
+    _TLS_BSS_size = _TLS_BSS_end - _TLS_BSS_begin;
+    _TLS_Size = _TLS_BSS_end - _TLS_Data_begin;
+    _TLS_Alignment = MAX (ALIGNOF (.tdata), ALIGNOF (.tbss));
+
+CPU counter
+===========
+
+The CPU support must implement the CPU counter interface.  A CPU counter is
+some free-running counter.  It ticks usually with a frequency close to the CPU
+or system bus clock.  On some architectures the actual implementation is board
+support package dependent.  The CPU counter is used for profiling of low-level
+functions.  It is also used to implement two busy wait functions``rtems_counter_delay_ticks()`` and ``rtems_counter_delay_nanoseconds()``
+which may be used in device drivers.  It may be also used as an entropy source
+for random number generators.
+
+The CPU counter interface uses a CPU port specific unsigned integer type``CPU_Counter_ticks`` to represent CPU counter values.  The CPU port must
+provide the following two functions
+
+- ``_CPU_Counter_read()`` to read the current CPU counter value, and
+
+- ``_CPU_Counter_difference()`` to get the difference between two CPU
+  counter values.
+
+Interrupt Profiling
+===================
+
+The RTEMS profiling needs support by the CPU port for the interrupt entry and
+exit times.  In case profiling is enabled via the RTEMS build configuration
+option ``--enable-profiling`` (in this case the pre-processor symbol``RTEMS_PROFILING`` is defined) the CPU port may provide data for the
+interrupt entry and exit times of the outer-most interrupt.  The CPU port can
+feed interrupt entry and exit times with the``_Profiling_Outer_most_interrupt_entry_and_exit()`` function
+(``#include <rtems/score/profiling.h>``).  For an example please have a look
+at ``cpukit/score/cpu/arm/arm_exc_interrupt.S``.
+
+Board Support Packages
+======================
+
+An RTEMS Board Support Package (BSP) must be designed to support a
+particular processor model and target board combination.
+
+In each of the architecture specific chapters, this section will present
+a discussion of architecture specific BSP issues.   For more information
+on developing a BSP, refer to BSP and Device Driver Development Guide
+and the chapter titled Board Support Packages in the RTEMS
+Applications Userâs Guide.
+
+System Reset
+------------
+
+An RTEMS based application is initiated or re-initiated when the processor
+is reset or transfer is passed to it from a boot monitor or ROM monitor.
+
+In each of the architecture specific chapters, this subsection describes
+the actions that the BSP must tak assuming the application gets control
+when the microprocessor is reset.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+ARM Specific Information
+########################
+
+This chapter discusses the`ARM architecture <http://en.wikipedia.org/wiki/ARM_architecture>`_
+dependencies in this port of RTEMS.  The ARMv4T (and compatible), ARMv7-A,
+ARMv7-R and ARMv7-M architecture versions are supported by RTEMS.  Processors
+with a MMU use a static configuration which is set up during system start.  SMP
+is supported.
+
+**Architecture Documents**
+
+For information on the ARM architecture refer to the`ARM Infocenter <http://infocenter.arm.com>`_.
+
+CPU Model Dependent Features
+============================
+
+This section presents the set of features which vary
+across ARM implementations and are of importance to RTEMS.  The set of CPU
+model feature macros are defined in the file:file:`cpukit/score/cpu/arm/rtems/score/arm.h` based upon the particular CPU
+model flags specified on the compilation command line.
+
+CPU Model Name
+--------------
+
+The macro ``CPU_MODEL_NAME`` is a string which designates
+the architectural level of this CPU model.  See in:file:`cpukit/score/cpu/arm/rtems/score/arm.h` for the values.
+
+Count Leading Zeroes Instruction
+--------------------------------
+
+The ARMv5 and later has the count leading zeroes ``clz`` instruction which
+could be used to speed up the find first bit operation.  The use of this
+instruction should significantly speed up the scheduling associated with a
+thread blocking.  This is currently not used.
+
+Floating Point Unit
+-------------------
+
+The following floating point units are supported.
+
+- VFPv3-D32/NEON (for example available on Cortex-A processors)
+
+- VFPv3-D16 (for example available on Cortex-R processors)
+
+- FPv4-SP-D16 (for example available on Cortex-M processors)
+
+Multilibs
+=========
+
+The following multilibs are available:
+
+# ``.``: ARMv4T, ARM instruction set
+
+# ``thumb``: ARMv4T, Thumb-1 instruction set
+
+# ``thumb/armv6-m``: ARMv6M, subset of Thumb-2 instruction set
+
+# ``thumb/armv7-a``: ARMv7-A, Thumb-2 instruction set
+
+# ``thumb/armv7-a/neon/hard``: ARMv7-A, Thumb-2 instruction set with
+  hard-float ABI Neon and VFP-D32 support
+
+# ``thumb/armv7-r``: ARMv7-R, Thumb-2 instruction set
+
+# ``thumb/armv7-r/vfpv3-d16/hard``: ARMv7-R, Thumb-2 instruction set
+  with hard-float ABI VFP-D16 support
+
+# ``thumb/armv7-m``: ARMv7-M, Thumb-2 instruction set with hardware
+  integer division (SDIV/UDIV)
+
+# ``thumb/armv7-m/fpv4-sp-d16``: ARMv7-M, Thumb-2 instruction set with
+  hardware integer division (SDIV/UDIV) and hard-float ABI FPv4-SP support
+
+# ``eb/thumb/armv7-r``: ARMv7-R, Big-endian Thumb-2 instruction set
+
+# ``eb/thumb/armv7-r/vfpv3-d16/hard``: ARMv7-R, Big-endian Thumb-2
+  instruction set with hard-float ABI VFP-D16 support
+
+Multilib 1. and 2. support the standard ARM7TDMI and ARM926EJ-S targets.
+
+Multilib 3. supports the Cortex-M0 and Cortex-M1 cores.
+
+Multilib 8. supports the Cortex-M3 and Cortex-M4 cores, which have a special
+hardware integer division instruction (this is not present in the A and R
+profiles).
+
+Multilib 9. supports the Cortex-M4 cores with a floating point unit.
+
+Multilib 4. and 5. support the Cortex-A processors.
+
+Multilib 6., 7., 10. and 11. support the Cortex-R processors.  Here also
+big-endian variants are available.
+
+Use for example the following GCC options
+.. code:: c
+
+    -mthumb -march=armv7-a -mfpu=neon -mfloat-abi=hard -mtune=cortex-a9
+
+to build an application or BSP for the ARMv7-A architecture and tune the code
+for a Cortex-A9 processor.  It is important to select the options used for the
+multilibs. For example
+.. code:: c
+
+    -mthumb -mcpu=cortex-a9
+
+alone will not select the ARMv7-A multilib.
+
+Calling Conventions
+===================
+
+Please refer to the`Procedure Call Standard for the ARM Architecture <http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042c/IHI0042C_aapcs.pdf>`_.
+
+Memory Model
+============
+
+A flat 32-bit memory model is supported.  The board support package must take
+care about the MMU if necessary.
+
+Interrupt Processing
+====================
+
+The ARMv4T (and compatible) architecture has seven exception types:
+
+- Reset
+
+- Undefined
+
+- Software Interrupt (SWI)
+
+- Prefetch Abort
+
+- Data Abort
+
+- Interrupt (IRQ)
+
+- Fast Interrupt (FIQ)
+
+Of these types only the IRQ has explicit operating system support.  It is
+intentional that the FIQ is not supported by the operating system.  Without
+operating system support for the FIQ it is not necessary to disable them during
+critical sections of the system.
+
+The ARMv7-M architecture has a completely different exception model.  Here
+interrupts are disabled with a write of 0x80 to the ``basepri_max``
+register.  This means that all exceptions and interrupts with a priority value
+of greater than or equal to 0x80 are disabled.  Thus exceptions and interrupts
+with a priority value of less than 0x80 are non-maskable with respect to the
+operating system and therefore must not use operating system services.  Several
+support libraries of chip vendors implicitly shift the priority value somehow
+before the value is written to the NVIC IPR register.  This can easily lead to
+confusion.
+
+Interrupt Levels
+----------------
+
+There are exactly two interrupt levels on ARM with respect to RTEMS.  Level
+zero corresponds to interrupts enabled.  Level one corresponds to interrupts
+disabled.
+
+Interrupt Stack
+---------------
+
+The board support package must initialize the interrupt stack. The memory for
+the stacks is usually reserved in the linker script.
+
+Default Fatal Error Processing
+==============================
+
+The default fatal error handler for this architecture performs the
+following actions:
+
+- disables operating system supported interrupts (IRQ),
+
+- places the error code in ``r0``, and
+
+- executes an infinite loop to simulate a halt processor instruction.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is supported on ARMv7-A.  Available platforms are the Altera Cyclone V and
+the Xilinx Zynq.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is supported.
+
+.. COMMENT: COPYRIGHT (c) 1988-2009.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Atmel AVR Specific Information
+##############################
+
+This chapter discusses the AVR architecture dependencies in this
+port of RTEMS.
+
+**Architecture Documents**
+
+For information on the AVR architecture, refer to the following
+documents available from Atmel.
+
+TBD
+
+- See other CPUs for documentation reference formatting examples.
+
+CPU Model Dependent Features
+============================
+
+CPUs of the AVR 53X only differ in the peripherals and thus in the
+device drivers. This port does not yet support the 56X dual core variants.
+
+Count Leading Zeroes Instruction
+--------------------------------
+
+The AVR CPU has the XXX instruction which could be used to speed
+up the find first bit operation.  The use of this instruction should
+significantly speed up the scheduling associated with a thread blocking.
+
+Calling Conventions
+===================
+
+Processor Background
+--------------------
+
+The AVR architecture supports a simple call and return mechanism.
+A subroutine is invoked via the call (``call``) instruction.
+This instruction saves the return address in the ``RETS`` register
+and transfers the execution to the given address.
+
+It is the called funcions responsability to use the link instruction
+to reserve space on the stack for the local variables.  Returning from
+a subroutine is done by using the RTS (``RTS``) instruction which
+loads the PC with the adress stored in RETS.
+
+It is is important to note that the ``call`` instruction does not
+automatically save or restore any registers.  It is the responsibility
+of the high-level language compiler to define the register preservation
+and usage convention.
+
+Register Usage
+--------------
+
+A called function may clobber all registers, except RETS, R4-R7, P3-P5,
+FP and SP.  It may also modify the first 12 bytes in the callerÃ¢ÂÂs stack
+frame which is used as an argument area for the first three arguments
+(which are passed in R0...R3 but may be placed on the stack by the
+called function).
+
+Parameter Passing
+-----------------
+
+RTEMS assumes that the AVR GCC calling convention is followed.
+The first three parameters are stored in registers R0, R1, and R2.
+All other parameters are put pushed on the stack.  The result is returned
+through register R0.
+
+Memory Model
+============
+
+The AVR family architecutre support a single unified 4 GB byte
+address space using 32-bit addresses. It maps all resources like internal
+and external memory and IO registers into separate sections of this
+common address space.
+
+The AVR architcture supports some form of memory
+protection via its Memory Management Unit. Since the
+AVR port runs in supervisior mode this memory
+protection mechanisms are not used.
+
+Interrupt Processing
+====================
+
+Discussed in this chapter are the AVRâs interrupt response and
+control mechanisms as they pertain to RTEMS.
+
+Vectoring of an Interrupt Handler
+---------------------------------
+
+TBD
+
+Disabling of Interrupts by RTEMS
+--------------------------------
+
+During interrupt disable critical sections, RTEMS disables interrupts to
+level N (N) before the execution of this section and restores them
+to the previous level upon completion of the section. RTEMS uses the
+instructions CLI and STI to enable and disable Interrupts. Emulation,
+Reset, NMI and Exception Interrupts are never disabled.
+
+Interrupt Stack
+---------------
+
+The AVR Architecture works with two different kind of stacks,
+User and Supervisor Stack. Since RTEMS and its Application run
+in supervisor mode, all interrupts will use the interrupted
+tasks stack for execution.
+
+Default Fatal Error Processing
+==============================
+
+The default fatal error handler for the AVR performs the following
+actions:
+
+- disables processor interrupts,
+
+- places the error code in *r0*, and
+
+- executes an infinite loop (``while(0);`` to
+  simulate a halt processor instruction.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is not supported due to a broken tool chain.
+
+Board Support Packages
+======================
+
+System Reset
+------------
+
+TBD
+
+.. COMMENT: COPYRIGHT (c) 1988-2006.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Blackfin Specific Information
+#############################
+
+This chapter discusses the Blackfin architecture dependencies in this
+port of RTEMS.
+
+**Architecture Documents**
+
+For information on the Blackfin architecture, refer to the following
+documents available from Analog Devices.
+
+TBD
+
+- *"ADSP-BF533 Blackfin Processor Hardware Reference."*:file:`http://www.analog.com/UploadedFiles/Associated_Docs/892485982bf533_hwr.pdf`
+
+CPU Model Dependent Features
+============================
+
+CPUs of the Blackfin 53X only differ in the peripherals and thus in the
+device drivers. This port does not yet support the 56X dual core variants.
+
+Count Leading Zeroes Instruction
+--------------------------------
+
+The Blackfin CPU has the BITTST instruction which could be used to speed
+up the find first bit operation.  The use of this instruction should
+significantly speed up the scheduling associated with a thread blocking.
+
+Calling Conventions
+===================
+
+This section is heavily based on content taken from the Blackfin uCLinux
+documentation wiki which is edited by Analog Devices and Arcturus
+Networks.  :file:`http://docs.blackfin.uclinux.org/`
+
+Processor Background
+--------------------
+
+The Blackfin architecture supports a simple call and return mechanism.
+A subroutine is invoked via the call (``call``) instruction.
+This instruction saves the return address in the ``RETS`` register
+and transfers the execution to the given address.
+
+It is the called funcions responsability to use the link instruction
+to reserve space on the stack for the local variables.  Returning from
+a subroutine is done by using the RTS (``RTS``) instruction which
+loads the PC with the adress stored in RETS.
+
+It is is important to note that the ``call`` instruction does not
+automatically save or restore any registers.  It is the responsibility
+of the high-level language compiler to define the register preservation
+and usage convention.
+
+Register Usage
+--------------
+
+A called function may clobber all registers, except RETS, R4-R7, P3-P5,
+FP and SP.  It may also modify the first 12 bytes in the callerÃ¢ÂÂs stack
+frame which is used as an argument area for the first three arguments
+(which are passed in R0...R3 but may be placed on the stack by the
+called function).
+
+Parameter Passing
+-----------------
+
+RTEMS assumes that the Blackfin GCC calling convention is followed.
+The first three parameters are stored in registers R0, R1, and R2.
+All other parameters are put pushed on the stack.  The result is returned
+through register R0.
+
+Memory Model
+============
+
+The Blackfin family architecutre support a single unified 4 GB byte
+address space using 32-bit addresses. It maps all resources like internal
+and external memory and IO registers into separate sections of this
+common address space.
+
+The Blackfin architcture supports some form of memory
+protection via its Memory Management Unit. Since the
+Blackfin port runs in supervisior mode this memory
+protection mechanisms are not used.
+
+Interrupt Processing
+====================
+
+Discussed in this chapter are the Blackfinâs interrupt response and
+control mechanisms as they pertain to RTEMS. The Blackfin architecture
+support 16 kinds of interrupts broken down into Core and general-purpose
+interrupts.
+
+Vectoring of an Interrupt Handler
+---------------------------------
+
+RTEMS maps levels 0 -15 directly to Blackfins event vectors EVT0 -
+EVT15. Since EVT0 - EVT6 are core events and it is suggested to use
+EVT15 and EVT15 for Software interrupts, 7 Interrupts (EVT7-EVT13)
+are left for periferical use.
+
+When installing an RTEMS interrupt handler RTEMS installs a generic
+Interrupt Handler which saves some context and enables nested interrupt
+servicing and then vectors to the users interrupt handler.
+
+Disabling of Interrupts by RTEMS
+--------------------------------
+
+During interrupt disable critical sections, RTEMS disables interrupts to
+level four (4) before the execution of this section and restores them
+to the previous level upon completion of the section. RTEMS uses the
+instructions CLI and STI to enable and disable Interrupts. Emulation,
+Reset, NMI and Exception Interrupts are never disabled.
+
+Interrupt Stack
+---------------
+
+The Blackfin Architecture works with two different kind of stacks,
+User and Supervisor Stack. Since RTEMS and its Application run
+in supervisor mode, all interrupts will use the interrupted
+tasks stack for execution.
+
+Default Fatal Error Processing
+==============================
+
+The default fatal error handler for the Blackfin performs the following
+actions:
+
+- disables processor interrupts,
+
+- places the error code in *r0*, and
+
+- executes an infinite loop (``while(0);`` to
+  simulate a halt processor instruction.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is not implemented.
+
+Board Support Packages
+======================
+
+System Reset
+------------
+
+TBD
+
+.. COMMENT: Copyright (c) 2015 University of York.
+
+.. COMMENT: Hesham ALMatary <hmka501@york.ac.uk>
+
+Epiphany Specific Information
+#############################
+
+This chapter discusses the`Epiphany Architecture <http://adapteva.com/docs/epiphany_sdk_ref.pdf>`_
+dependencies in this port of RTEMS. Epiphany is a chip that can come with 16 and
+64 cores, each of which can run RTEMS separately or they can work together to
+run a SMP RTEMS application.
+
+**Architecture Documents**
+
+For information on the Epiphany architecture refer to the`Epiphany Architecture Reference <http://adapteva.com/docs/epiphany_arch_ref.pdf>`_.
+
+Calling Conventions
+===================
+
+Please refer to the`Epiphany SDK <http://adapteva.com/docs/epiphany_sdk_ref.pdf>`_
+Appendix A: Application Binary Interface
+
+Floating Point Unit
+-------------------
+
+A floating point unit is currently not supported.
+
+Memory Model
+============
+
+A flat 32-bit memory model is supported, no caches. Each core has its own 32 KiB
+strictly ordered local memory along with an access to a shared 32 MiB external
+DRAM.
+
+Interrupt Processing
+====================
+
+Every Epiphany core has 10 exception types:
+
+- Reset
+
+- Software Exception
+
+- Data Page Fault
+
+- Timer 0
+
+- Timer 1
+
+- Message Interrupt
+
+- DMA0 Interrupt
+
+- DMA1 Interrupt
+
+- WANT Interrupt
+
+- User Interrupt
+
+Interrupt Levels
+----------------
+
+There are only two levels: interrupts enabled and interrupts disabled.
+
+Interrupt Stack
+---------------
+
+The Epiphany RTEMS port uses a dedicated software interrupt stack.
+The stack for interrupts is allocated during interrupt driver initialization.
+When an  interrupt is entered, the _ISR_Handler routine is responsible for
+switching from the interrupted task stack to RTEMS software interrupt stack.
+
+Default Fatal Error Processing
+==============================
+
+The default fatal error handler for this architecture performs the
+following actions:
+
+- disables operating system supported interrupts (IRQ),
+
+- places the error code in ``r0``, and
+
+- executes an infinite loop to simulate a halt processor instruction.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Intel/AMD x86 Specific Information
+##################################
+
+This chapter discusses the Intel x86 architecture dependencies
+in this port of RTEMS.  This family has multiple implementations
+from multiple vendors and suffers more from having evolved rather
+than being designed for growth.
+
+For information on the i386 processor, refer to the
+following documents:
+
+- *386 Programmerâs Reference Manual, Intel, Order No.  230985-002*.
+
+- *386 Microprocessor Hardware Reference Manual, Intel,
+  Order No. 231732-003*.
+
+- *80386 System Software Writerâs Guide, Intel, Order No.  231499-001*.
+
+- *80387 Programmerâs Reference Manual, Intel, Order No.  231917-001*.
+
+CPU Model Dependent Features
+============================
+
+This section presents the set of features which vary
+across i386 implementations and are of importance to RTEMS.
+The set of CPU model feature macros are defined in the file``cpukit/score/cpu/i386/i386.h`` based upon the particular CPU
+model specified on the compilation command line.
+
+bswap Instruction
+-----------------
+
+The macro ``I386_HAS_BSWAP`` is set to 1 to indicate that
+this CPU model has the ``bswap`` instruction which
+endian swaps a thirty-two bit quantity.  This instruction
+appears to be present in all CPU models
+i486âs and above.
+
+Calling Conventions
+===================
+
+Processor Background
+--------------------
+
+The i386 architecture supports a simple yet effective
+call and return mechanism.  A subroutine is invoked via the call
+(``call``) instruction.  This instruction pushes the return address
+on the stack.  The return from subroutine (``ret``) instruction pops
+the return address off the current stack and transfers control
+to that instruction.  It is is important to note that the i386
+call and return mechanism does not automatically save or restore
+any registers.  It is the responsibility of the high-level
+language compiler to define the register preservation and usage
+convention.
+
+Calling Mechanism
+-----------------
+
+All RTEMS directives are invoked using a call instruction and return to
+the user application via the ret instruction.
+
+Register Usage
+--------------
+
+As discussed above, the call instruction does not automatically save
+any registers.  RTEMS uses the registers EAX, ECX, and EDX as scratch
+registers.  These registers are not preserved by RTEMS directives
+therefore, the contents of these registers should not be assumed upon
+return from any RTEMS directive.
+
+Parameter Passing
+-----------------
+
+RTEMS assumes that arguments are placed on the
+current stack before the directive is invoked via the call
+instruction.  The first argument is assumed to be closest to the
+return address on the stack.  This means that the first argument
+of the C calling sequence is pushed last.  The following
+pseudo-code illustrates the typical sequence used to call a
+RTEMS directive with three (3) arguments:
+.. code:: c
+
+    push third argument
+    push second argument
+    push first argument
+    invoke directive
+    remove arguments from the stack
+
+The arguments to RTEMS are typically pushed onto the
+stack using a push instruction.  These arguments must be removed
+from the stack after control is returned to the caller.  This
+removal is typically accomplished by adding the size of the
+argument list in bytes to the stack pointer.
+
+Memory Model
+============
+
+Flat Memory Model
+-----------------
+
+RTEMS supports the i386 protected mode, flat memory
+model with paging disabled.  In this mode, the i386
+automatically converts every address from a logical to a
+physical address each time it is used.  The i386 uses
+information provided in the segment registers and the Global
+Descriptor Table to convert these addresses.  RTEMS assumes the
+existence of the following segments:
+
+- a single code segment at protection level (0) which
+  contains all application and executive code.
+
+- a single data segment at protection level zero (0) which
+  contains all application and executive data.
+
+The i386 segment registers and associated selectors
+must be initialized when the initialize_executive directive is
+invoked.  RTEMS treats the segment registers as system registers
+and does not modify or context switch them.
+
+This i386 memory model supports a flat 32-bit address
+space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
+gigabytes).  Each address is represented by a 32-bit value and
+is byte addressable.  The address may be used to reference a
+single byte, half-word (2-bytes), or word (4 bytes).
+
+Interrupt Processing
+====================
+
+Although RTEMS hides many of the processor
+dependent details of interrupt processing, it is important to
+understand how the RTEMS interrupt manager is mapped onto the
+processorâs unique architecture. Discussed in this chapter are
+the the processorâs response and control mechanisms as they
+pertain to RTEMS.
+
+Vectoring of Interrupt Handler
+------------------------------
+
+Although the i386 supports multiple privilege levels,
+RTEMS and all user software executes at privilege level 0.  This
+decision was made by the RTEMS designers to enhance
+compatibility with processors which do not provide sophisticated
+protection facilities like those of the i386.  This decision
+greatly simplifies the discussion of i386 processing, as one
+need only consider interrupts without privilege transitions.
+
+Upon receipt of an interrupt  the i386 automatically
+performs the following actions:
+
+- pushes the EFLAGS register
+
+- pushes the far address of the interrupted instruction
+
+- vectors to the interrupt service routine (ISR).
+
+A nested interrupt is processed similarly by the
+i386.
+
+Interrupt Stack Frame
+---------------------
+
+The structure of the Interrupt Stack Frame for the
+i386 which is placed on the interrupt stack by the processor in
+response to an interrupt is as follows:
+
++----------------------+-------+
+| Old EFLAGS Register  | ESP+8 |
++----------+-----------+-------+
+|   UNUSED |  Old CS   | ESP+4 |
++----------+-----------+-------+
+|       Old EIP        | ESP   |
++----------------------+-------+
+
+
+Interrupt Levels
+----------------
+
+Although RTEMS supports 256 interrupt levels, the
+i386 only supports two â enabled and disabled.  Interrupts are
+enabled when the interrupt-enable flag (IF) in the extended
+flags (EFLAGS) is set.  Conversely, interrupt processing is
+inhibited when the IF is cleared.  During a non-maskable
+interrupt, all other interrupts, including other non-maskable
+ones, are inhibited.
+
+RTEMS interrupt levels 0 and 1 such that level zero
+(0) indicates that interrupts are fully enabled and level one
+that interrupts are disabled.  All other RTEMS interrupt levels
+are undefined and their behavior is unpredictable.
+
+Interrupt Stack
+---------------
+
+The i386 family does not support a dedicated hardware
+interrupt stack.  On this processor, RTEMS allocates and manages
+a dedicated interrupt stack.  As part of vectoring a non-nested
+interrupt service routine, RTEMS switches from the stack of the
+interrupted task to a dedicated interrupt stack.  When a
+non-nested interrupt returns, RTEMS switches back to the stack
+of the interrupted stack.  The current stack pointer is not
+altered by RTEMS on nested interrupt.
+
+Default Fatal Error Processing
+==============================
+
+The default fatal error handler for this architecture disables processor
+interrupts, places the error code in EAX, and executes a HLT instruction
+to halt the processor.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is not implemented.
+
+Board Support Packages
+======================
+
+System Reset
+------------
+
+An RTEMS based application is initiated when the i386 processor is reset.
+When the i386 is reset,
+
+- The EAX register is set to indicate the results of the processorâs
+  power-up self test.  If the self-test was not executed, the contents of
+  this register are undefined.  Otherwise, a non-zero value indicates the
+  processor is faulty and a zero value indicates a successful self-test.
+
+- The DX register holds a component identifier and revision level.  DH
+  contains 3 to indicate an i386 component and DL contains a unique revision
+  level indicator.
+
+- Control register zero (CR0) is set such that the processor is in real
+  mode with paging disabled.  Other portions of CR0 are used to indicate the
+  presence of a numeric coprocessor.
+
+- All bits in the extended flags register (EFLAG) which are not
+  permanently set are cleared.  This inhibits all maskable interrupts.
+
+- The Interrupt Descriptor Register (IDTR) is set to point at address
+  zero.
+
+- All segment registers are set to zero.
+
+- The instruction pointer is set to 0x0000FFF0.  The first instruction
+  executed after a reset is actually at 0xFFFFFFF0 because the i386 asserts
+  the upper twelve address until the first intersegment (FAR) JMP or CALL
+  instruction.  When a JMP or CALL is executed, the upper twelve address
+  lines are lowered and the processor begins executing in the first megabyte
+  of memory.
+
+Typically, an intersegment JMP to the applicationâs initialization code is
+placed at address 0xFFFFFFF0.
+
+Processor Initialization
+------------------------
+
+This initialization code is responsible for initializing all data
+structures required by the i386 in protected mode and for actually entering
+protected mode.  The i386 must be placed in protected mode and the segment
+registers and associated selectors must be initialized before the
+initialize_executive directive is invoked.
+
+The initialization code is responsible for initializing the Global
+Descriptor Table such that the i386 is in the thirty-two bit flat memory
+model with paging disabled.  In this mode, the i386 automatically converts
+every address from a logical to a physical address each time it is used.
+For more information on the memory model used by RTEMS, please refer to the
+Memory Model chapter in this document.
+
+Since the processor is in real mode upon reset, the processor must be
+switched to protected mode before RTEMS can execute.  Before switching to
+protected mode, at least one descriptor table and two descriptors must be
+created.  Descriptors are needed for a code segment and a data segment. (
+This will give you the flat memory model.)  The stack can be placed in a
+normal read/write data segment, so no descriptor for the stack is needed.
+Before the GDT can be used, the base address and limit must be loaded into
+the GDTR register using an LGDT instruction.
+
+If the hardware allows an NMI to be generated, you need to create the IDT
+and a gate for the NMI interrupt handler.  Before the IDT can be used, the
+base address and limit for the idt must be loaded into the IDTR register
+using an LIDT instruction.
+
+Protected mode is entered by setting thye PE bit in the CR0 register.
+Either a LMSW or MOV CR0 instruction may be used to set this bit. Because
+the processor overlaps the interpretation of several instructions, it is
+necessary to discard the instructions from the read-ahead cache. A JMP
+instruction immediately after the LMSW changes the flow and empties the
+processor if intructions which have been pre-fetched and/or decoded.  At
+this point, the processor is in protected mode and begins to perform
+protected mode application initialization.
+
+If the application requires that the IDTR be some value besides zero, then
+it should set it to the required value at this point.  All tasks share the
+same i386 IDTR value.  Because interrupts are enabled automatically by
+RTEMS as part of the initialize_executive directive, the IDTR MUST be set
+properly before this directive is invoked to insure correct interrupt
+vectoring.  If processor caching is to be utilized, then it should be
+enabled during the reset application initialization code.  The reset code
+which is executed before the call to initialize_executive has the following
+requirements:
+
+For more information regarding the i386 data structures and their
+contents, refer to Intelâs 386 Programmerâs Reference Manual.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+.. COMMENT: Jukka Pietarinen <jukka.pietarinen@mrf.fi>, 2008,
+
+.. COMMENT: Micro-Research Finland Oy
+
+Lattice Mico32 Specific Information
+###################################
+
+This chaper discusses the Lattice Mico32 architecture dependencies in
+this port of RTEMS. The Lattice Mico32 is a 32-bit Harvard, RISC
+architecture "soft" microprocessor, available for free with an open IP
+core licensing agreement. Although mainly targeted for Lattice FPGA
+devices the microprocessor can be implemented on other vendorsâ FPGAs,
+too.
+
+**Architecture Documents**
+
+For information on the Lattice Mico32 architecture, refer to the
+following documents available from Lattice Semiconductor:file:`http://www.latticesemi.com/`.
+
+- *"LatticeMico32 Processor Reference Manual"*:file:`http://www.latticesemi.com/dynamic/view_document.cfm?document_id=20890`
+
+CPU Model Dependent Features
+============================
+
+The Lattice Mico32 architecture allows for different configurations of
+the processor. This port is based on the assumption that the following options are implemented:
+
+- hardware multiplier
+
+- hardware divider
+
+- hardware barrel shifter
+
+- sign extension instructions
+
+- instruction cache
+
+- data cache
+
+- debug
+
+Register Architecture
+=====================
+
+This section gives a brief introduction to the register architecture
+of the Lattice Mico32 processor.
+
+The Lattice Mico32 is a RISC archictecture processor with a
+32-register file of 32-bit registers.
+
+Register Name
+
+Function
+
+r0
+
+holds value zero
+
+r1-r25
+
+general purpose
+
+r26/gp
+
+general pupose / global pointer
+
+r27/fp
+
+general pupose / frame pointer
+
+r28/sp
+
+stack pointer
+
+r29/ra
+
+return address
+
+r30/ea
+
+exception address
+
+r31/ba
+
+breakpoint address
+
+Note that on processor startup all register values are undefined
+including r0, thus r0 has to be initialized to zero.
+
+Calling Conventions
+===================
+
+Calling Mechanism
+-----------------
+
+A call instruction places the return address to register r29 and a
+return from subroutine (ret) is actually a branch to r29/ra.
+
+Register Usage
+--------------
+
+A subroutine may freely use registers r1 to r10 which are *not*
+preserved across subroutine invocations.
+
+Parameter Passing
+-----------------
+
+When calling a C function the first eight arguments are stored in
+registers r1 to r8. Registers r1 and r2 hold the return value.
+
+Memory Model
+============
+
+The Lattice Mico32 processor supports a flat memory model with a 4
+Gbyte address space with 32-bit addresses.
+
+The following data types are supported:
+
+Type
+
+Bits
+
+C Compiler Type
+
+unsigned byte
+
+8
+
+unsigned char
+
+signed byte
+
+8
+
+char
+
+unsigned half-word
+
+16
+
+unsigned short
+
+signed half-word
+
+16
+
+short
+
+unsigned word
+
+32
+
+unsigned int / unsigned long
+
+signed word
+
+32
+
+int / long
+
+Data accesses need to be aligned, with unaligned accesses result are
+undefined.
+
+Interrupt Processing
+====================
+
+The Lattice Mico32 has 32 interrupt lines which are however served by
+only one exception vector. When an interrupt occurs following happens:
+
+- address of next instruction placed in r30/ea
+
+- IE field of IE CSR saved to EIE field and IE field cleared preventing further exceptions from occuring.
+
+- branch to interrupt exception address EBA CSR + 0xC0
+
+The interrupt exception handler determines from the state of the
+interrupt pending registers (IP CSR) and interrupt enable register (IE
+CSR) which interrupt to serve and jumps to the interrupt routine
+pointed to by the corresponding interrupt vector.
+
+For now there is no dedicated interrupt stack so every task in
+the system MUST have enough stack space to accommodate the worst
+case stack usage of that particular task and the interrupt
+service routines COMBINED.
+
+Nested interrupts are not supported.
+
+Default Fatal Error Processing
+==============================
+
+Upon detection of a fatal error by either the application or RTEMS during
+initialization the ``rtems_fatal_error_occurred`` directive supplied
+by the Fatal Error Manager is invoked.  The Fatal Error Manager will
+invoke the user-supplied fatal error handlers.  If no user-supplied
+handlers are configured or all of them return without taking action to
+shutdown the processor or reset, a default fatal error handler is invoked.
+
+Most of the action performed as part of processing the fatal error are
+described in detail in the Fatal Error Manager chapter in the Userâs
+Guide.  However, the if no user provided extension or BSP specific fatal
+error handler takes action, the final default action is to invoke a
+CPU architecture specific function.  Typically this function disables
+interrupts and halts the processor.
+
+In each of the architecture specific chapters, this describes the precise
+operations of the default CPU specific fatal error handler.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is not implemented.
+
+Board Support Packages
+======================
+
+An RTEMS Board Support Package (BSP) must be designed to support a
+particular processor model and target board combination.
+
+In each of the architecture specific chapters, this section will present
+a discussion of architecture specific BSP issues.   For more information
+on developing a BSP, refer to BSP and Device Driver Development Guide
+and the chapter titled Board Support Packages in the RTEMS
+Applications Userâs Guide.
+
+System Reset
+------------
+
+An RTEMS based application is initiated or re-initiated when the processor
+is reset.
+
+.. COMMENT: Copyright (c) 2014 embedded brains GmbH.  All rights reserved.
+
+Renesas M32C Specific Information
+#################################
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is not implemented.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+M68xxx and Coldfire Specific Information
+########################################
+
+This chapter discusses the Freescale (formerly Motorola) MC68xxx
+and Coldfire architectural dependencies.  The MC68xxx family has a
+wide variety of CPU models within it based upon different CPU core
+implementations.  Ignoring the Coldfire parts, the part numbers for
+these models are generally divided into MC680xx and MC683xx.  The MC680xx
+models are more general purpose processors with no integrated peripherals.
+The MC683xx models, on the other hand, are more specialized and have a
+variety of peripherals on chip including sophisticated timers and serial
+communications controllers.
+
+**Architecture Documents**
+
+For information on the MC68xxx and Coldfire architecture, refer to the following documents available from Freescale website (:file:`http//www.freescale.com/`):
+
+- *M68000 Family Reference, Motorola, FR68K/D*.
+
+- *MC68020 Userâs Manual, Motorola, MC68020UM/AD*.
+
+- *MC68881/MC68882 Floating-Point Coprocessor Userâs Manual,
+  Motorola, MC68881UM/AD*.
+
+CPU Model Dependent Features
+============================
+
+This section presents the set of features which vary
+across m68k/Coldfire implementations that are of importance to RTEMS.
+The set of CPU model feature macros are defined in the file``cpukit/score/cpu/m68k/m68k.h`` based upon the particular CPU
+model selected on the compilation command line.
+
+BFFFO Instruction
+-----------------
+
+The macro ``M68K_HAS_BFFFO`` is set to 1 to indicate that
+this CPU model has the bfffo instruction.
+
+Vector Base Register
+--------------------
+
+The macro ``M68K_HAS_VBR`` is set to 1 to indicate that
+this CPU model has a vector base register (vbr).
+
+Separate Stacks
+---------------
+
+The macro ``M68K_HAS_SEPARATE_STACKS`` is set to 1 to
+indicate that this CPU model has separate interrupt, user, and
+supervisor mode stacks.
+
+Pre-Indexing Address Mode
+-------------------------
+
+The macro ``M68K_HAS_PREINDEXING`` is set to 1 to indicate that
+this CPU model has the pre-indexing address mode.
+
+Extend Byte to Long Instruction
+-------------------------------
+
+The macro ``M68K_HAS_EXTB_L`` is set to 1 to indicate that this CPU model
+has the extb.l instruction.  This instruction is supposed to be available
+in all models based on the cpu32 core as well as mc68020 and up models.
+
+Calling Conventions
+===================
+
+The MC68xxx architecture supports a simple yet effective call and
+return mechanism.  A subroutine is invoked via the branch to subroutine
+(``bsr``) or the jump to subroutine (``jsr``) instructions.
+These instructions push the return address on the current stack.
+The return from subroutine (``rts``) instruction pops the return
+address off the current stack and transfers control to that instruction.
+It is is important to note that the MC68xxx call and return mechanism does
+not automatically save or restore any registers.  It is the responsibility
+of the high-level language compiler to define the register preservation
+and usage convention.
+
+Calling Mechanism
+-----------------
+
+All RTEMS directives are invoked using either a ``bsr`` or ``jsr``
+instruction and return to the user application via the rts instruction.
+
+Register Usage
+--------------
+
+As discussed above, the ``bsr`` and ``jsr`` instructions do not
+automatically save any registers.  RTEMS uses the registers D0, D1,
+A0, and A1 as scratch registers.  These registers are not preserved by
+RTEMS directives therefore, the contents of these registers should not
+be assumed upon return from any RTEMS directive.
+
+Parameter Passing
+-----------------
+
+RTEMS assumes that arguments are placed on the current stack before
+the directive is invoked via the bsr or jsr instruction.  The first
+argument is assumed to be closest to the return address on the stack.
+This means that the first argument of the C calling sequence is pushed
+last.  The following pseudo-code illustrates the typical sequence used
+to call a RTEMS directive with three (3) arguments:
+.. code:: c
+
+    push third argument
+    push second argument
+    push first argument
+    invoke directive
+    remove arguments from the stack
+
+The arguments to RTEMS are typically pushed onto the stack using a move
+instruction with a pre-decremented stack pointer as the destination.
+These arguments must be removed from the stack after control is returned
+to the caller.  This removal is typically accomplished by adding the
+size of the argument list in bytes to the current stack pointer.
+
+Memory Model
+============
+
+The MC68xxx family supports a flat 32-bit address
+space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
+gigabytes).  Each address is represented by a 32-bit value and
+is byte addressable.  The address may be used to reference a
+single byte, word (2-bytes), or long word (4 bytes).  Memory
+accesses within this address space are performed in big endian
+fashion by the processors in this family.
+
+Some of the MC68xxx family members such as the
+MC68020, MC68030, and MC68040 support virtual memory and
+segmentation.  The MC68020 requires external hardware support
+such as the MC68851 Paged Memory Management Unit coprocessor
+which is typically used to perform address translations for
+these systems.  RTEMS does not support virtual memory or
+segmentation on any of the MC68xxx family members.
+
+Interrupt Processing
+====================
+
+Discussed in this section are the MC68xxxâs interrupt response and
+control mechanisms as they pertain to RTEMS.
+
+Vectoring of an Interrupt Handler
+---------------------------------
+
+Depending on whether or not the particular CPU supports a separate
+interrupt stack, the MC68xxx family has two different interrupt handling
+models.
+
+Models Without Separate Interrupt Stacks
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Upon receipt of an interrupt the MC68xxx family members without separate
+interrupt stacks automatically perform the following actions:
+
+- To Be Written
+
+Models With Separate Interrupt Stacks
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Upon receipt of an interrupt the MC68xxx family members with separate
+interrupt stacks automatically perform the following actions:
+
+- saves the current status register (SR),
+
+- clears the master/interrupt (M) bit of the SR to
+  indicate the switch from master state to interrupt state,
+
+- sets the privilege mode to supervisor,
+
+- suppresses tracing,
+
+- sets the interrupt mask level equal to the level of the
+  interrupt being serviced,
+
+- pushes an interrupt stack frame (ISF), which includes
+  the program counter (PC), the status register (SR), and the
+  format/exception vector offset (FVO) word, onto the supervisor
+  and interrupt stacks,
+
+- switches the current stack to the interrupt stack and
+  vectors to an interrupt service routine (ISR).  If the ISR was
+  installed with the interrupt_catch directive, then the RTEMS
+  interrupt handler will begin execution.  The RTEMS interrupt
+  handler saves all registers which are not preserved according to
+  the calling conventions and invokes the applicationâs ISR.
+
+A nested interrupt is processed similarly by these
+CPU models with the exception that only a single ISF is placed
+on the interrupt stack and the current stack need not be
+switched.
+
+The FVO word in the Interrupt Stack Frame is examined
+by RTEMS to determine when an outer most interrupt is being
+exited. Since the FVO is used by RTEMS for this purpose, the
+user application code MUST NOT modify this field.
+
+The following shows the Interrupt Stack Frame for
+MC68xxx CPU models with separate interrupt stacks:
+
++----------------------+-----+
+|    Status Register   | 0x0 |
++----------------------+-----+
+| Program Counter High | 0x2 |
++----------------------+-----+
+| Program Counter Low  | 0x4 |
++----------------------+-----+
+| Format/Vector Offset | 0x6 |
++----------------------+-----+
+
+
+CPU Models Without VBR and RAM at 0
+-----------------------------------
+
+This is from a post by Zoltan Kocsi <zoltan@bendor.com.au> and is
+a nice trick in certain situations.  In his words:
+
+I think somebody on this list asked about the interupt vector handling
+w/o VBR and RAM at 0.  The usual trick is to initialise the vector table
+(except the first 2 two entries, of course) to point to the same location
+BUT you also add the vector number times 0x1000000 to them. That is,
+bits 31-24 contain the vector number and 23-0 the address of the common
+handler.  Since the PC is 32 bit wide but the actual address bus is only
+24, the top byte will be in the PC but will be ignored when jumping onto
+your routine.
+
+Then your common interrupt routine gets this info by loading the PC
+into some register and based on that info, you can jump to a vector in
+a vector table pointed by a virtual VBR:
+.. code:: c
+
+    //
+    //  Real vector table at 0
+    //
+    .long   initial_sp
+    .long   initial_pc
+    .long   myhandler+0x02000000
+    .long   myhandler+0x03000000
+    .long   myhandler+0x04000000
+    ...
+    .long   myhandler+0xff000000
+    //
+    // This handler will jump to the interrupt routine   of which
+    // the address is stored at VBR[ vector_no ]
+    // The registers and stackframe will be intact, the interrupt
+    // routine will see exactly what it would see if it was called
+    // directly from the HW vector table at 0.
+    //
+    .comm    VBR,4,2        // This defines the 'virtual' VBR
+    // From C: extern void \*VBR;
+    myhandler:                  // At entry, PC contains the full vector
+    move.l  %d0,-(%sp)      // Save d0
+    move.l  %a0,-(%sp)      // Save a0
+    lea     0(%pc),%a0      // Get the value of the PC
+    move.l  %a0,%d0         // Copy it to a data reg, d0 is VV??????
+    swap    %d0             // Now d0 is ????VV??
+    and.w   #0xff00,%d0     // Now d0 is ????VV00 (1)
+    lsr.w   #6,%d0          // Now d0.w contains the VBR table offset
+    move.l  VBR,%a0         // Get the address from VBR to a0
+    move.l  (%a0,%d0.w),%a0 // Fetch the vector
+    move.l  4(%sp),%d0      // Restore d0
+    move.l  %a0,4(%sp)      // Place target address to the stack
+    move.l  (%sp)+,%a0      // Restore a0, target address is on TOS
+    ret                     // This will jump to the handler and
+    // restore the stack
+    (1) If 'myhandler' is guaranteed to be in the first 64K, e.g. just
+    after the vector table then that insn is not needed.
+
+There are probably shorter ways to do this, but it I believe is enough
+to illustrate the trick. Optimisation is left as an exercise to the
+reader :-)
+
+Interrupt Levels
+----------------
+
+Eight levels (0-7) of interrupt priorities are
+supported by MC68xxx family members with level seven (7) being
+the highest priority.  Level zero (0) indicates that interrupts
+are fully enabled.  Interrupt requests for interrupts with
+priorities less than or equal to the current interrupt mask
+level are ignored.
+
+Although RTEMS supports 256 interrupt levels, the
+MC68xxx family only supports eight.  RTEMS interrupt levels 0
+through 7 directly correspond to MC68xxx interrupt levels.  All
+other RTEMS interrupt levels are undefined and their behavior is
+unpredictable.
+
+Default Fatal Error Processing
+==============================
+
+The default fatal error handler for this architecture disables processor
+interrupts to level 7, places the error code in D0, and executes a``stop`` instruction to simulate a halt processor instruction.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is supported.
+
+Board Support Packages
+======================
+
+System Reset
+------------
+
+An RTEMS based application is initiated or re-initiated when the MC68020
+processor is reset.  When the MC68020 is reset, the processor performs
+the following actions:
+
+- The tracing bits of the status register are cleared to
+  disable tracing.
+
+- The supervisor interrupt state is entered by setting the
+  supervisor (S) bit and clearing the master/interrupt (M) bit of
+  the status register.
+
+- The interrupt mask of the status register is set to
+  level 7 to effectively disable all maskable interrupts.
+
+- The vector base register (VBR) is set to zero.
+
+- The cache control register (CACR) is set to zero to
+  disable and freeze the processor cache.
+
+- The interrupt stack pointer (ISP) is set to the value
+  stored at vector 0 (bytes 0-3) of the exception vector table
+  (EVT).
+
+- The program counter (PC) is set to the value stored at
+  vector 1 (bytes 4-7) of the EVT.
+
+- The processor begins execution at the address stored in
+  the PC.
+
+Processor Initialization
+------------------------
+
+The address of the applicationâs initialization code should be stored in
+the first vector of the EVT which will allow the immediate vectoring to
+the application code.  If the application requires that the VBR be some
+value besides zero, then it should be set to the required value at this
+point.  All tasks share the same MC68020âs VBR value.  Because interrupts
+are enabled automatically by RTEMS as part of the context switch to the
+first task, the VBR MUST be set by either RTEMS of the BSP before this
+occurs ensure correct interrupt vectoring.  If processor caching is
+to be utilized, then it should be enabled during the reset application
+initialization code.
+
+In addition to the requirements described in the
+Board Support Packages chapter of the Applications Userâs
+Manual for the reset code which is executed before the call to
+initialize executive, the MC68020 version has the following
+specific requirements:
+
+- Must leave the S bit of the status register set so that
+  the MC68020 remains in the supervisor state.
+
+- Must set the M bit of the status register to remove the
+  MC68020 from the interrupt state.
+
+- Must set the master stack pointer (MSP) such that a
+  minimum stack size of MINIMUM_STACK_SIZE bytes is provided for
+  the initialize executive directive.
+
+- Must initialize the MC68020âs vector table.
+
+.. COMMENT: Copyright (c) 2014 embedded brains GmbH.  All rights reserved.
+
+Xilinx MicroBlaze Specific Information
+######################################
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is not implemented.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+MIPS Specific Information
+#########################
+
+This chapter discusses the MIPS architecture dependencies
+in this port of RTEMS.  The MIPS family has a wide variety
+of implementations by a wide range of vendors.  Consequently,
+there are many, many CPU models within it.
+
+**Architecture Documents**
+
+IDT docs are online at http://www.idt.com/products/risc/Welcome.html
+
+For information on the XXX architecture, refer to the following documents
+available from VENDOR (:file:`http//www.XXX.com/`):
+
+- *XXX Family Reference, VENDOR, PART NUMBER*.
+
+CPU Model Dependent Features
+============================
+
+This section presents the set of features which vary
+across MIPS implementations and are of importance to RTEMS.
+The set of CPU model feature macros are defined in the file``cpukit/score/cpu/mips/mips.h`` based upon the particular CPU
+model specified on the compilation command line.
+
+Another Optional Feature
+------------------------
+
+The macro XXX
+
+Calling Conventions
+===================
+
+Processor Background
+--------------------
+
+TBD
+
+Calling Mechanism
+-----------------
+
+TBD
+
+Register Usage
+--------------
+
+TBD
+
+Parameter Passing
+-----------------
+
+TBD
+
+Memory Model
+============
+
+Flat Memory Model
+-----------------
+
+The MIPS family supports a flat 32-bit address
+space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
+gigabytes).  Each address is represented by a 32-bit value and
+is byte addressable.  The address may be used to reference a
+single byte, word (2-bytes), or long word (4 bytes).  Memory
+accesses within this address space are performed in big endian
+fashion by the processors in this family.
+
+Some of the MIPS family members such as the support virtual memory and
+segmentation.  RTEMS does not support virtual memory or
+segmentation on any of these family members.
+
+Interrupt Processing
+====================
+
+Although RTEMS hides many of the processor dependent
+details of interrupt processing, it is important to understand
+how the RTEMS interrupt manager is mapped onto the processorâs
+unique architecture. Discussed in this chapter are the MIPSâs
+interrupt response and control mechanisms as they pertain to
+RTEMS.
+
+Vectoring of an Interrupt Handler
+---------------------------------
+
+Upon receipt of an interrupt the XXX family
+members with separate interrupt stacks automatically perform the
+following actions:
+
+- TBD
+
+A nested interrupt is processed similarly by these
+CPU models with the exception that only a single ISF is placed
+on the interrupt stack and the current stack need not be
+switched.
+
+Interrupt Levels
+----------------
+
+TBD
+
+Default Fatal Error Processing
+==============================
+
+The default fatal error handler for this target architecture disables
+processor interrupts, places the error code in *XXX*, and executes a``XXX`` instruction to simulate a halt processor instruction.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is not implemented.
+
+Board Support Packages
+======================
+
+System Reset
+------------
+
+An RTEMS based application is initiated or
+re-initiated when the processor is reset.  When the
+processor is reset, it performs the following actions:
+
+- TBD
+
+Processor Initialization
+------------------------
+
+TBD
+
+.. COMMENT: Copyright (c) 2014 embedded brains GmbH.  All rights reserved.
+
+Altera Nios II Specific Information
+###################################
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is not implemented.
+
+.. COMMENT: COPYRIGHT (c) 2014 Hesham ALMatary <heshamelmatary@gmail.com>
+
+.. COMMENT: All rights reserved.
+
+OpenRISC 1000 Specific Information
+##################################
+
+This chapter discusses the`OpenRISC 1000 architecture <http://opencores.org/or1k/Main_Page>`_
+dependencies in this port of RTEMS. There are many implementations
+for OpenRISC like or1200 and mor1kx. Currently RTEMS supports basic
+features that all implementations should have.
+
+**Architecture Documents**
+
+For information on the OpenRISC 1000 architecture refer to the`OpenRISC 1000 architecture manual <http://openrisc.github.io/or1k.html>`_.
+
+Calling Conventions
+===================
+
+Please refer to the`Function Calling Sequence <http://openrisc.github.io/or1k.html#__RefHeading__504887_595890882>`_.
+
+Floating Point Unit
+-------------------
+
+A floating point unit is currently not supported.
+
+Memory Model
+============
+
+A flat 32-bit memory model is supported.
+
+Interrupt Processing
+====================
+
+OpenRISC 1000 architecture has 13 exception types:
+
+- Reset
+
+- Bus Error
+
+- Data Page Fault
+
+- Instruction Page Fault
+
+- Tick Timer
+
+- Alignment
+
+- Illegal Instruction
+
+- External Interrupt
+
+- D-TLB Miss
+
+- I-TLB Miss
+
+- Range
+
+- System Call
+
+- Floating Point
+
+- Trap
+
+Interrupt Levels
+----------------
+
+There are only two levels: interrupts enabled and interrupts disabled.
+
+Interrupt Stack
+---------------
+
+The OpenRISC RTEMS port uses a dedicated software interrupt stack.
+The stack for interrupts is allocated during interrupt driver initialization.
+When an  interrupt is entered, the _ISR_Handler routine is responsible for
+switching from the interrupted task stack to RTEMS software interrupt stack.
+
+Default Fatal Error Processing
+==============================
+
+The default fatal error handler for this architecture performs the
+following actions:
+
+- disables operating system supported interrupts (IRQ),
+
+- places the error code in ``r0``, and
+
+- executes an infinite loop to simulate a halt processor instruction.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+.. COMMENT: COPYRIGHT (c) 1989-2007.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+PowerPC Specific Information
+############################
+
+This chapter discusses the PowerPC architecture dependencies
+in this port of RTEMS.  The PowerPC family has a wide variety
+of implementations by a range of vendors.  Consequently,
+there are many, many CPU models within it.
+
+It is highly recommended that the PowerPC RTEMS
+application developer obtain and become familiar with the
+documentation for the processor being used as well as the
+specification for the revision of the PowerPC architecture which
+corresponds to that processor.
+
+**PowerPC Architecture Documents**
+
+For information on the PowerPC architecture, refer to
+the following documents available from Motorola and IBM:
+
+- *PowerPC Microprocessor Family: The Programming Environment*
+  (Motorola Document MPRPPCFPE-01).
+
+- *IBM PPC403GB Embedded Controller Userâs Manual*.
+
+- *PoweRisControl MPC500 Family RCPU RISC Central Processing
+  Unit Reference Manual* (Motorola Document RCPUURM/AD).
+
+- *PowerPC 601 RISC Microprocessor Userâs Manual*
+  (Motorola Document MPR601UM/AD).
+
+- *PowerPC 603 RISC Microprocessor Userâs Manual*
+  (Motorola Document MPR603UM/AD).
+
+- *PowerPC 603e RISC Microprocessor Userâs Manual*
+  (Motorola Document MPR603EUM/AD).
+
+- *PowerPC 604 RISC Microprocessor Userâs Manual*
+  (Motorola Document MPR604UM/AD).
+
+- *PowerPC MPC821 Portable Systems Microprocessor Userâs Manual*
+  (Motorola Document MPC821UM/AD).
+
+- *PowerQUICC MPC860 Userâs Manual* (Motorola Document MPC860UM/AD).
+
+Motorola maintains an on-line electronic library for the PowerPC
+at the following URL:
+
+-  http://www.mot.com/powerpc/library/library.html
+
+This site has a a wealth of information and examples.  Many of the
+manuals are available from that site in electronic format.
+
+**PowerPC Processor Simulator Information**
+
+PSIM is a program which emulates the Instruction Set Architecture
+of the PowerPC microprocessor family.  It is reely available in source
+code form under the terms of the GNU General Public License (version
+2 or later).  PSIM can be integrated with the GNU Debugger (gdb) to
+execute and debug PowerPC executables on non-PowerPC hosts.  PSIM
+supports the addition of user provided device models which can be
+used to allow one to develop and debug embedded applications using
+the simulator.
+
+The latest version of PSIM is included in GDB and enabled on pre-built
+binaries provided by the RTEMS Project.
+
+CPU Model Dependent Features
+============================
+
+This section presents the set of features which vary
+across PowerPC implementations and are of importance to RTEMS.
+The set of CPU model feature macros are defined in the file``cpukit/score/cpu/powerpc/powerpc.h`` based upon the particular CPU
+model specified on the compilation command line.
+
+Alignment
+---------
+
+The macro PPC_ALIGNMENT is set to the PowerPC modelâs worst case alignment
+requirement for data types on a byte boundary.  This value is used
+to derive the alignment restrictions for memory allocated from
+regions and partitions.
+
+Cache Alignment
+---------------
+
+The macro PPC_CACHE_ALIGNMENT is set to the line size of the cache.  It is
+used to align the entry point of critical routines so that as much code
+as possible can be retrieved with the initial read into cache.  This
+is done for the interrupt handler as well as the context switch routines.
+
+In addition, the "shortcut" data structure used by the PowerPC implementation
+to ease access to data elements frequently accessed by RTEMS routines
+implemented in assembly language is aligned using this value.
+
+Maximum Interrupts
+------------------
+
+The macro PPC_INTERRUPT_MAX is set to the number of exception sources
+supported by this PowerPC model.
+
+Has Double Precision Floating Point
+-----------------------------------
+
+The macro PPC_HAS_DOUBLE is set to 1 to indicate that the PowerPC model
+has support for double precision floating point numbers.  This is
+important because the floating point registers need only be four bytes
+wide (not eight) if double precision is not supported.
+
+Critical Interrupts
+-------------------
+
+The macro PPC_HAS_RFCI is set to 1 to indicate that the PowerPC model
+has the Critical Interrupt capability as defined by the IBM 403 models.
+
+Use Multiword Load/Store Instructions
+-------------------------------------
+
+The macro PPC_USE_MULTIPLE is set to 1 to indicate that multiword load and
+store instructions should be used to perform context switch operations.
+The relative efficiency of multiword load and store instructions versus
+an equivalent set of single word load and store instructions varies based
+upon the PowerPC model.
+
+Instruction Cache Size
+----------------------
+
+The macro PPC_I_CACHE is set to the size in bytes of the instruction cache.
+
+Data Cache Size
+---------------
+
+The macro PPC_D_CACHE is set to the size in bytes of the data cache.
+
+Debug Model
+-----------
+
+The macro PPC_DEBUG_MODEL is set to indicate the debug support features
+present in this CPU model.  The following debug support feature sets
+are currently supported:
+
+*``PPC_DEBUG_MODEL_STANDARD``*
+    indicates that the single-step trace enable (SE) and branch trace
+    enable (BE) bits in the MSR are supported by this CPU model.
+
+*``PPC_DEBUG_MODEL_SINGLE_STEP_ONLY``*
+    indicates that only the single-step trace enable (SE) bit in the MSR
+    is supported by this CPU model.
+
+*``PPC_DEBUG_MODEL_IBM4xx``*
+    indicates that the debug exception enable (DE) bit in the MSR is supported
+    by this CPU model.  At this time, this particular debug feature set
+    has only been seen in the IBM 4xx series.
+
+Low Power Model
+~~~~~~~~~~~~~~~
+
+The macro PPC_LOW_POWER_MODE is set to indicate the low power model
+supported by this CPU model.  The following low power modes are currently
+supported.
+
+*``PPC_LOW_POWER_MODE_NONE``*
+    indicates that this CPU model has no low power mode support.
+
+*``PPC_LOW_POWER_MODE_STANDARD``*
+    indicates that this CPU model follows the low power model defined for
+    the PPC603e.
+
+Multilibs
+=========
+
+The following multilibs are available:
+
+# ``.``: 32-bit PowerPC with FPU
+
+# ``nof``: 32-bit PowerPC with software floating point support
+
+# ``m403``: Instruction set for PPC403 with FPU
+
+# ``m505``: Instruction set for MPC505 with FPU
+
+# ``m603e``: Instruction set for MPC603e with FPU
+
+# ``m603e/nof``: Instruction set for MPC603e with software floating
+  point support
+
+# ``m604``: Instruction set for MPC604 with FPU
+
+# ``m604/nof``: Instruction set for MPC604 with software floating point
+  support
+
+# ``m860``: Instruction set for MPC860 with FPU
+
+# ``m7400``: Instruction set for MPC7500 with FPU
+
+# ``m7400/nof``: Instruction set for MPC7500 with software floating
+  point support
+
+# ``m8540``: Instruction set for e200, e500 and e500v2 cores with
+  single-precision FPU and SPE
+
+# ``m8540/gprsdouble``: Instruction set for e200, e500 and e500v2 cores
+  with double-precision FPU and SPE
+
+# ``m8540/nof/nospe``: Instruction set for e200, e500 and e500v2 cores
+  with software floating point support and no SPE
+
+# ``me6500/m32``: 32-bit instruction set for e6500 core with FPU and
+  AltiVec
+
+# ``me6500/m32/nof/noaltivec``: 32-bit instruction set for e6500 core
+  with software floating point support and no AltiVec
+
+Calling Conventions
+===================
+
+RTEMS supports the Embedded Application Binary Interface (EABI)
+calling convention.  Documentation for EABI is available by sending
+a message with a subject line of "EABI" to eabi@goth.sis.mot.com.
+
+Programming Model
+-----------------
+
+This section discusses the programming model for the
+PowerPC architecture.
+
+Non-Floating Point Registers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The PowerPC architecture defines thirty-two non-floating point registers
+directly visible to the programmer.  In thirty-two bit implementations, each
+register is thirty-two bits wide.  In sixty-four bit implementations, each
+register is sixty-four bits wide.
+
+These registers are referred to as ``gpr0`` to ``gpr31``.
+
+Some of the registers serve defined roles in the EABI programming model.
+The following table describes the role of each of these registers:
+.. code:: c
+
+    +---------------+----------------+------------------------------+
+    | Register Name | Alternate Name |         Description          |
+    +---------------+----------------+------------------------------+
+    |      r1       |      sp        |         stack pointer        |
+    +---------------+----------------+------------------------------+
+    |               |                |  global pointer to the Small |
+    |      r2       |      na        |     Constant Area (SDA2)     |
+    +---------------+----------------+------------------------------+
+    |    r3 - r12   |      na        | parameter and result passing |
+    +---------------+----------------+------------------------------+
+    |               |                |  global pointer to the Small |
+    |      r13      |      na        |         Data Area (SDA)      |
+    +---------------+----------------+------------------------------+
+
+Floating Point Registers
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+The PowerPC architecture includes thirty-two, sixty-four bit
+floating point registers.  All PowerPC floating point instructions
+interpret these registers as 32 double precision floating point registers,
+regardless of whether the processor has 64-bit or 32-bit implementation.
+
+The floating point status and control register (fpscr) records exceptions
+and the type of result generated by floating-point operations.
+Additionally, it controls the rounding mode of operations and allows the
+reporting of floating exceptions to be enabled or disabled.
+
+Special Registers
+~~~~~~~~~~~~~~~~~
+
+The PowerPC architecture includes a number of special registers
+which are critical to the programming model:
+
+*Machine State Register*
+    The MSR contains the processor mode, power management mode, endian mode,
+    exception information, privilege level, floating point available and
+    floating point excepiton mode, address translation information and
+    the exception prefix.
+
+*Link Register*
+    The LR contains the return address after a function call.  This register
+    must be saved before a subsequent subroutine call can be made.  The
+    use of this register is discussed further in the *Call and Return
+    Mechanism* section below.
+
+*Count Register*
+    The CTR contains the iteration variable for some loops.  It may also be used
+    for indirect function calls and jumps.
+
+Call and Return Mechanism
+-------------------------
+
+The PowerPC architecture supports a simple yet effective call
+and return mechanism.  A subroutine is invoked
+via the "branch and link" (``bl``) and
+"brank and link absolute" (``bla``)
+instructions.  This instructions place the return address
+in the Link Register (LR).  The callee returns to the caller by
+executing a "branch unconditional to the link register" (``blr``)
+instruction.  Thus the callee returns to the caller via a jump
+to the return address which is stored in the LR.
+
+The previous contents of the LR are not automatically saved
+by either the ``bl`` or ``bla``.  It is the responsibility
+of the callee to save the contents of the LR before invoking
+another subroutine.  If the callee invokes another subroutine,
+it must restore the LR before executing the ``blr`` instruction
+to return to the caller.
+
+It is important to note that the PowerPC subroutine
+call and return mechanism does not automatically save and
+restore any registers.
+
+The LR may be accessed as special purpose register 8 (``SPR8``) using the
+"move from special register" (``mfspr``) and
+"move to special register" (``mtspr``) instructions.
+
+Calling Mechanism
+-----------------
+
+All RTEMS directives are invoked using the regular
+PowerPC EABI calling convention via the ``bl`` or``bla`` instructions.
+
+Register Usage
+--------------
+
+As discussed above, the call instruction does not
+automatically save any registers.  It is the responsibility
+of the callee to save and restore any registers which must be preserved
+across subroutine calls.  The callee is responsible for saving
+callee-preserved registers to the program stack and restoring them
+before returning to the caller.
+
+Parameter Passing
+-----------------
+
+RTEMS assumes that arguments are placed in the
+general purpose registers with the first argument in
+register 3 (``r3``), the second argument in general purpose
+register 4 (``r4``), and so forth until the seventh
+argument is in general purpose register 10 (``r10``).
+If there are more than seven arguments, then subsequent arguments
+are placed on the program stack.  The following pseudo-code
+illustrates the typical sequence used to call a RTEMS directive
+with three (3) arguments:
+.. code:: c
+
+    load third argument into r5
+    load second argument into r4
+    load first argument into r3
+    invoke directive
+
+Memory Model
+============
+
+Flat Memory Model
+-----------------
+
+The PowerPC architecture supports a variety of memory models.
+RTEMS supports the PowerPC using a flat memory model with
+paging disabled.  In this mode, the PowerPC automatically
+converts every address from a logical to a physical address
+each time it is used.  The PowerPC uses information provided
+in the Block Address Translation (BAT) to convert these addresses.
+
+Implementations of the PowerPC architecture may be thirty-two or sixty-four bit.
+The PowerPC architecture supports a flat thirty-two or sixty-four bit address
+space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
+gigabytes) in thirty-two bit implementations or to 0xFFFFFFFFFFFFFFFF
+in sixty-four bit implementations.  Each address is represented
+by either a thirty-two bit or sixty-four bit value and is byte addressable.
+The address may be used to reference a single byte, half-word
+(2-bytes), word (4 bytes), or in sixty-four bit implementations a
+doubleword (8 bytes).  Memory accesses within the address space are
+performed in big or little endian fashion by the PowerPC based
+upon the current setting of the Little-endian mode enable bit (LE)
+in the Machine State Register (MSR).  While the processor is in
+big endian mode, memory accesses which are not properly aligned
+generate an "alignment exception" (vector offset 0x00600).  In
+little endian mode, the PowerPC architecture does not require
+the processor to generate alignment exceptions.
+
+The following table lists the alignment requirements for a variety
+of data accesses:
+
+.. code:: c
+
+    +--------------+-----------------------+
+    |   Data Type  | Alignment Requirement |
+    +--------------+-----------------------+
+    |     byte     |          1            |
+    |   half-word  |          2            |
+    |     word     |          4            |
+    |  doubleword  |          8            |
+    +--------------+-----------------------+
+
+Doubleword load and store operations are only available in
+PowerPC CPU models which are sixty-four bit implementations.
+
+RTEMS does not directly support any PowerPC Memory Management
+Units, therefore, virtual memory or segmentation systems
+involving the PowerPC  are not supported.
+
+.. COMMENT: COPYRIGHT (c) 1989-2007.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Interrupt Processing
+====================
+
+Although RTEMS hides many of the processor dependent
+details of interrupt processing, it is important to understand
+how the RTEMS interrupt manager is mapped onto the processorâs
+unique architecture. Discussed in this chapter are the PowerPCâs
+interrupt response and control mechanisms as they pertain to
+RTEMS.
+
+RTEMS and associated documentation uses the terms interrupt and vector.
+In the PowerPC architecture, these terms correspond to exception and
+exception handler, respectively.  The terms will be used interchangeably
+in this manual.
+
+Synchronous Versus Asynchronous Exceptions
+------------------------------------------
+
+In the PowerPC architecture exceptions can be either precise or
+imprecise and either synchronous or asynchronous.  Asynchronous
+exceptions occur when an external event interrupts the processor.
+Synchronous exceptions are caused by the actions of an
+instruction. During an exception SRR0 is used to calculate where
+instruction processing should resume.  All instructions prior to
+the resume instruction will have completed execution.  SRR1 is used to
+store the machine status.
+
+There are two asynchronous nonmaskable, highest-priority exceptions
+system reset and machine check.  There are two asynchrononous maskable
+low-priority exceptions external interrupt and decrementer.  Nonmaskable
+execptions are never delayed, therefore if two nonmaskable, asynchronous
+exceptions occur in immediate succession, the state information saved by
+the first exception may be overwritten when the subsequent exception occurs.
+
+The PowerPC arcitecure defines one imprecise exception, the imprecise
+floating point enabled exception.  All other synchronous exceptions are
+precise.  The synchronization occuring during asynchronous precise
+exceptions conforms to the requirements for context synchronization.
+
+Vectoring of Interrupt Handler
+------------------------------
+
+Upon determining that an exception can be taken the PowerPC automatically
+performs the following actions:
+
+- an instruction address is loaded into SRR0
+
+- bits 33-36 and 42-47 of SRR1 are loaded with information
+  specific to the exception.
+
+- bits 0-32, 37-41, and 48-63 of SRR1 are loaded with corresponding
+  bits from the MSR.
+
+- the MSR is set based upon the exception type.
+
+- instruction fetch and execution resumes, using the new MSR value, at a location specific to the execption type.
+
+If the interrupt handler was installed as an RTEMS
+interrupt handler, then upon receipt of the interrupt, the
+processor passes control to the RTEMS interrupt handler which
+performs the following actions:
+
+- saves the state of the interrupted task on itâs stack,
+
+- saves all registers which are not normally preserved
+  by the calling sequence so the userâs interrupt service
+  routine can be written in a high-level language.
+
+- if this is the outermost (i.e. non-nested) interrupt,
+  then the RTEMS interrupt handler switches from the current stack
+  to the interrupt stack,
+
+- enables exceptions,
+
+- invokes the vectors to a user interrupt service routine (ISR).
+
+Asynchronous interrupts are ignored while exceptions are
+disabled.  Synchronous interrupts which occur while are
+disabled result in the CPU being forced into an error mode.
+
+A nested interrupt is processed similarly with the
+exception that the current stack need not be switched to the
+interrupt stack.
+
+Interrupt Levels
+----------------
+
+The PowerPC architecture supports only a single external
+asynchronous interrupt source.  This interrupt source
+may be enabled and disabled via the External Interrupt Enable (EE)
+bit in the Machine State Register (MSR).  Thus only two level (enabled
+and disabled) of external device interrupt priorities are
+directly supported by the PowerPC architecture.
+
+Some PowerPC implementations include a Critical Interrupt capability
+which is often used to receive interrupts from high priority external
+devices.
+
+The RTEMS interrupt level mapping scheme for the PowerPC is not
+a numeric level as on most RTEMS ports.  It is a bit mapping in
+which the least three significiant bits of the interrupt level
+are mapped directly to the enabling of specific interrupt
+sources as follows:
+
+*Critical Interrupt*
+    Setting bit 0 (the least significant bit) of the interrupt level
+    enables the Critical Interrupt source, if it is available on this
+    CPU model.
+
+*Machine Check*
+    Setting bit 1 of the interrupt level enables Machine Check execptions.
+
+*External Interrupt*
+    Setting bit 2 of the interrupt level enables External Interrupt execptions.
+
+All other bits in the RTEMS task interrupt level are ignored.
+
+Default Fatal Error Processing
+==============================
+
+The default fatal error handler for this architecture performs the
+following actions:
+
+- places the error code in r3, and
+
+- executes a trap instruction which results in a Program Exception.
+
+If the Program Exception returns, then the following actions are performed:
+
+- disables all processor exceptions by loading a 0 into the MSR, and
+
+- goes into an infinite loop to simulate a halt processor instruction.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is supported.  Available platforms are the Freescale QorIQ P series (e.g.
+P1020) and T series (e.g. T2080, T4240).
+
+Thread-Local Storage
+====================
+
+Thread-local storage is supported.
+
+Board Support Packages
+======================
+
+System Reset
+------------
+
+An RTEMS based application is initiated or
+re-initiated when the PowerPC processor is reset.  The PowerPC
+architecture defines a Reset Exception, but leaves the
+details of the CPU state as implementation specific.  Please
+refer to the Userâs Manual for the CPU model in question.
+
+In general, at power-up the PowerPC begin execution at address
+0xFFF00100 in supervisor mode with all exceptions disabled.  For
+soft resets, the CPU will vector to either 0xFFF00100 or 0x00000100
+depending upon the setting of the Exception Prefix bit in the MSR.
+If during a soft reset, a Machine Check Exception occurs, then the
+CPU may execute a hard reset.
+
+Processor Initialization
+------------------------
+
+If this PowerPC implementation supports on-chip caching
+and this is to be utilized, then it should be enabled during the
+reset application initialization code.  On-chip caching has been
+observed to prevent some emulators from working properly, so it
+may be necessary to run with caching disabled to use these emulators.
+
+In addition to the requirements described in the*Board Support Packages* chapter of the RTEMS C
+Applications Userâs Manual for the reset code
+which is executed before the call to ``rtems_initialize_executive``,
+the PowrePC version has the following specific requirements:
+
+- Must leave the PR bit of the Machine State Register (MSR) set
+  to 0 so the PowerPC remains in the supervisor state.
+
+- Must set stack pointer (sp or r1) such that a minimum stack
+  size of MINIMUM_STACK_SIZE bytes is provided for the RTEMS initialization
+  sequence.
+
+- Must disable all external interrupts (i.e. clear the EI (EE)
+  bit of the machine state register).
+
+- Must enable traps so window overflow and underflow
+  conditions can be properly handled.
+
+- Must initialize the PowerPCâs initial Exception Table with default
+  handlers.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+SuperH Specific Information
+###########################
+
+This chapter discusses the SuperH architecture dependencies
+in this port of RTEMS.  The SuperH family has a wide variety
+of implementations by a wide range of vendors.  Consequently,
+there are many, many CPU models within it.
+
+**Architecture Documents**
+
+For information on the SuperH architecture,
+refer to the following documents available from VENDOR
+(:file:`http//www.XXX.com/`):
+
+- *SuperH Family Reference, VENDOR, PART NUMBER*.
+
+CPU Model Dependent Features
+============================
+
+This chapter presents the set of features which vary
+across SuperH implementations and are of importance to RTEMS.
+The set of CPU model feature macros are defined in the file``cpukit/score/cpu/sh/sh.h`` based upon the particular CPU
+model specified on the compilation command line.
+
+Another Optional Feature
+------------------------
+
+The macro XXX
+
+Calling Conventions
+===================
+
+Calling Mechanism
+-----------------
+
+All RTEMS directives are invoked using a ``XXX``
+instruction and return to the user application via the``XXX`` instruction.
+
+Register Usage
+--------------
+
+The SH1 has 16 general registers (r0..r15).
+
+- r0..r3 used as general volatile registers
+
+- r4..r7 used to pass up to 4 arguments to functions, arguments
+  above 4 are
+  passed via the stack)
+
+- r8..13 caller saved registers (i.e. push them to the stack if you
+  need them inside of a function)
+
+- r14 frame pointer
+
+- r15 stack pointer
+
+Parameter Passing
+-----------------
+
+XXX
+
+Memory Model
+============
+
+Flat Memory Model
+-----------------
+
+The SuperH family supports a flat 32-bit address
+space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
+gigabytes).  Each address is represented by a 32-bit value and
+is byte addressable.  The address may be used to reference a
+single byte, word (2-bytes), or long word (4 bytes).  Memory
+accesses within this address space are performed in big endian
+fashion by the processors in this family.
+
+Some of the SuperH family members support virtual memory and
+segmentation.  RTEMS does not support virtual memory or
+segmentation on any of the SuperH family members.  It is the
+responsibility of the BSP to initialize the mapping for
+a flat memory model.
+
+Interrupt Processing
+====================
+
+Although RTEMS hides many of the processor dependent
+details of interrupt processing, it is important to understand
+how the RTEMS interrupt manager is mapped onto the processorâs
+unique architecture. Discussed in this chapter are the MIPSâs
+interrupt response and control mechanisms as they pertain to
+RTEMS.
+
+Vectoring of an Interrupt Handler
+---------------------------------
+
+Upon receipt of an interrupt the XXX family
+members with separate interrupt stacks automatically perform the
+following actions:
+
+- TBD
+
+A nested interrupt is processed similarly by these
+CPU models with the exception that only a single ISF is placed
+on the interrupt stack and the current stack need not be
+switched.
+
+Interrupt Levels
+----------------
+
+TBD
+
+Default Fatal Error Processing
+==============================
+
+The default fatal error handler for this architecture disables processor
+interrupts, places the error code in *XXX*, and executes a ``XXX``
+instruction to simulate a halt processor instruction.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is not implemented.
+
+Board Support Packages
+======================
+
+System Reset
+------------
+
+An RTEMS based application is initiated or
+re-initiated when the processor is reset.  When the
+processor is reset, it performs the following actions:
+
+- TBD
+
+Processor Initialization
+------------------------
+
+TBD
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+SPARC Specific Information
+##########################
+
+The Real Time Executive for Multiprocessor Systems
+(RTEMS) is designed to be portable across multiple processor
+architectures.  However, the nature of real-time systems makes
+it essential that the application designer understand certain
+processor dependent implementation details.  These processor
+dependencies include calling convention, board support package
+issues, interrupt processing, exact RTEMS memory requirements,
+performance data, header files, and the assembly language
+interface to the executive.
+
+This document discusses the SPARC architecture dependencies in this
+port of RTEMS.  This architectural port is for SPARC Version 7 and
+8. Implementations for SPARC V9 are in the sparc64 target.
+
+It is highly recommended that the SPARC RTEMS
+application developer obtain and become familiar with the
+documentation for the processor being used as well as the
+specification for the revision of the SPARC architecture which
+corresponds to that processor.
+
+**SPARC Architecture Documents**
+
+For information on the SPARC architecture, refer to
+the following documents available from SPARC International, Inc.
+(http://www.sparc.com):
+
+- SPARC Standard Version 7.
+
+- SPARC Standard Version 8.
+
+**ERC32 Specific Information**
+
+The European Space Agencyâs ERC32 is a three chip
+computing core implementing a SPARC V7 processor and associated
+support circuitry for embedded space applications. The integer
+and floating-point units (90C601E & 90C602E) are based on the
+Cypress 7C601 and 7C602, with additional error-detection and
+recovery functions. The memory controller (MEC) implements
+system support functions such as address decoding, memory
+interface, DMA interface, UARTs, timers, interrupt control,
+write-protection, memory reconfiguration and error-detection.
+The core is designed to work at 25MHz, but using space qualified
+memories limits the system frequency to around 15 MHz, resulting
+in a performance of 10 MIPS and 2 MFLOPS.
+
+Information on the ERC32 and a number of development
+support tools, such as the SPARC Instruction Simulator (SIS),
+are freely available on the Internet.  The following documents
+and SIS are available via anonymous ftp or pointing your web
+browser at ftp://ftp.estec.esa.nl/pub/ws/wsd/erc32.
+
+- ERC32 System Design Document
+
+- MEC Device Specification
+
+Additionally, the SPARC RISC Userâs Guide from Matra
+MHS documents the functionality of the integer and floating
+point units including the instruction set information.  To
+obtain this document as well as ERC32 components and VHDL models
+contact:
+.. code:: c
+
+    Matra MHS SA
+    3 Avenue du Centre, BP 309,
+    78054 St-Quentin-en-Yvelines,
+    Cedex, France
+    VOICE: +31-1-30607087
+    FAX: +31-1-30640693
+
+Amar Guennon (amar.guennon@matramhs.fr) is familiar with the ERC32.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+CPU Model Dependent Features
+============================
+
+Microprocessors are generally classified into
+families with a variety of CPU models or implementations within
+that family.  Within a processor family, there is a high level
+of binary compatibility.  This family may be based on either an
+architectural specification or on maintaining compatibility with
+a popular processor.  Recent microprocessor families such as the
+SPARC or PowerPC are based on an architectural specification
+which is independent or any particular CPU model or
+implementation.  Older families such as the M68xxx and the iX86
+evolved as the manufacturer strived to produce higher
+performance processor models which maintained binary
+compatibility with older models.
+
+RTEMS takes advantage of the similarity of the
+various models within a CPU family.  Although the models do vary
+in significant ways, the high level of compatibility makes it
+possible to share the bulk of the CPU dependent executive code
+across the entire family.
+
+CPU Model Feature Flags
+-----------------------
+
+Each processor family supported by RTEMS has a
+list of features which vary between CPU models
+within a family.  For example, the most common model dependent
+feature regardless of CPU family is the presence or absence of a
+floating point unit or coprocessor.  When defining the list of
+features present on a particular CPU model, one simply notes
+that floating point hardware is or is not present and defines a
+single constant appropriately.  Conditional compilation is
+utilized to include the appropriate source code for this CPU
+modelâs feature set.  It is important to note that this means
+that RTEMS is thus compiled using the appropriate feature set
+and compilation flags optimal for this CPU model used.  The
+alternative would be to generate a binary which would execute on
+all family members using only the features which were always
+present.
+
+This section presents the set of features which vary
+across SPARC implementations and are of importance to RTEMS.
+The set of CPU model feature macros are defined in the file
+cpukit/score/cpu/sparc/sparc.h based upon the particular CPU
+model defined on the compilation command line.
+
+CPU Model Name
+~~~~~~~~~~~~~~
+
+The macro CPU_MODEL_NAME is a string which designates
+the name of this CPU model.  For example, for the European Space
+Agencyâs ERC32 SPARC model, this macro is set to the string
+"erc32".
+
+Floating Point Unit
+~~~~~~~~~~~~~~~~~~~
+
+The macro SPARC_HAS_FPU is set to 1 to indicate that
+this CPU model has a hardware floating point unit and 0
+otherwise.
+
+Bitscan Instruction
+~~~~~~~~~~~~~~~~~~~
+
+The macro SPARC_HAS_BITSCAN is set to 1 to indicate
+that this CPU model has the bitscan instruction.  For example,
+this instruction is supported by the Fujitsu SPARClite family.
+
+Number of Register Windows
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The macro SPARC_NUMBER_OF_REGISTER_WINDOWS is set to
+indicate the number of register window sets implemented by this
+CPU model.  The SPARC architecture allows a for a maximum of
+thirty-two register window sets although most implementations
+only include eight.
+
+Low Power Mode
+~~~~~~~~~~~~~~
+
+The macro SPARC_HAS_LOW_POWER_MODE is set to one to
+indicate that this CPU model has a low power mode.  If low power
+is enabled, then there must be CPU model specific implementation
+of the IDLE task in cpukit/score/cpu/sparc/cpu.c.  The low
+power mode IDLE task should be of the form:
+.. code:: c
+
+    while ( TRUE ) {
+    enter low power mode
+    }
+
+The code required to enter low power mode is CPU model specific.
+
+CPU Model Implementation Notes
+------------------------------
+
+The ERC32 is a custom SPARC V7 implementation based on the Cypress 601/602
+chipset.  This CPU has a number of on-board peripherals and was developed by
+the European Space Agency to target space applications.  RTEMS currently
+provides support for the following peripherals:
+
+- UART Channels A and B
+
+- General Purpose Timer
+
+- Real Time Clock
+
+- Watchdog Timer (so it can be disabled)
+
+- Control Register (so powerdown mode can be enabled)
+
+- Memory Control Register
+
+- Interrupt Control
+
+The General Purpose Timer and Real Time Clock Timer provided with the ERC32
+share the Timer Control Register.  Because the Timer Control Register is write
+only, we must mirror it in software and insure that writes to one timer do not
+alter the current settings and status of the other timer.  Routines are
+provided in erc32.h which promote the view that the two timers are completely
+independent.  By exclusively using these routines to access the Timer Control
+Register, the application can view the system as having a General Purpose
+Timer Control Register and a Real Time Clock Timer Control Register
+rather than the single shared value.
+
+The RTEMS Idle thread take advantage of the low power mode provided by the
+ERC32.  Low power mode is entered during idle loops and is enabled at
+initialization time.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Calling Conventions
+===================
+
+Each high-level language compiler generates subroutine entry and exit code
+based upon a set of rules known as the application binary interface (ABI)
+calling convention.   These rules address the following issues:
+
+- register preservation and usage
+
+- parameter passing
+
+- call and return mechanism
+
+An ABI calling convention is of importance when interfacing to subroutines
+written in another language either assembly or high-level.  It determines also
+the set of registers to be saved or restored during a context switch and
+interrupt processing.
+
+The ABI relevant for RTEMS on SPARC is defined by SYSTEM V APPLICATION BINARY
+INTERFACE, SPARC Processor Supplement, Third Edition.
+
+Programming Model
+-----------------
+
+This section discusses the programming model for the
+SPARC architecture.
+
+Non-Floating Point Registers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The SPARC architecture defines thirty-two
+non-floating point registers directly visible to the programmer.
+These are divided into four sets:
+
+- input registers
+
+- local registers
+
+- output registers
+
+- global registers
+
+Each register is referred to by either two or three
+names in the SPARC reference manuals.  First, the registers are
+referred to as r0 through r31 or with the alternate notation
+r[0] through r[31].  Second, each register is a member of one of
+the four sets listed above.  Finally, some registers have an
+architecturally defined role in the programming model which
+provides an alternate name.  The following table describes the
+mapping between the 32 registers and the register sets:
+
+.. code:: c
+
+    +-----------------+----------------+------------------+
+    | Register Number | Register Names |   Description    |
+    +-----------------+----------------+------------------+
+    |     0 - 7       |    g0 - g7     | Global Registers |
+    +-----------------+----------------+------------------+
+    |     8 - 15      |    o0 - o7     | Output Registers |
+    +-----------------+----------------+------------------+
+    |    16 - 23      |    l0 - l7     | Local Registers  |
+    +-----------------+----------------+------------------+
+    |    24 - 31      |    i0 - i7     | Input Registers  |
+    +-----------------+----------------+------------------+
+
+As mentioned above, some of the registers serve
+defined roles in the programming model.  The following table
+describes the role of each of these registers:
+
+.. code:: c
+
+    +---------------+----------------+----------------------+
+    | Register Name | Alternate Name |      Description     |
+    +---------------+----------------+----------------------+
+    |     g0        |      na        |    reads return 0    |
+    |               |                |  writes are ignored  |
+    +---------------+----------------+----------------------+
+    |     o6        |      sp        |     stack pointer    |
+    +---------------+----------------+----------------------+
+    |     i6        |      fp        |     frame pointer    |
+    +---------------+----------------+----------------------+
+    |     i7        |      na        |    return address    |
+    +---------------+----------------+----------------------+
+
+The registers g2 through g4 are reserved for applications.  GCC uses them as
+volatile registers by default.  So they are treated like volatile registers in
+RTEMS as well.
+
+The register g6 is reserved for the operating system and contains the address
+of the per-CPU control block of the current processor.  This register is
+initialized during system start and then remains unchanged.  It is not
+saved/restored by the context switch or interrupt processing code.
+
+The register g7 is reserved for the operating system and contains the thread
+pointer used for thread-local storage (TLS) as mandated by the SPARC ABI.
+
+Floating Point Registers
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+The SPARC V7 architecture includes thirty-two,
+thirty-two bit registers.  These registers may be viewed as
+follows:
+
+- 32 single precision floating point or integer registers
+  (f0, f1,  ... f31)
+
+- 16 double precision floating point registers (f0, f2,
+  f4, ... f30)
+
+- 8 extended precision floating point registers (f0, f4,
+  f8, ... f28)
+
+The floating point status register (FSR) specifies
+the behavior of the floating point unit for rounding, contains
+its condition codes, version specification, and trap information.
+
+According to the ABI all floating point registers and the floating point status
+register (FSR) are volatile.  Thus the floating point context of a thread is the
+empty set.  The rounding direction is a system global state and must not be
+modified by threads.
+
+A queue of the floating point instructions which have
+started execution but not yet completed is maintained.  This
+queue is needed to support the multiple cycle nature of floating
+point operations and to aid floating point exception trap
+handlers.  Once a floating point exception has been encountered,
+the queue is frozen until it is emptied by the trap handler.
+The floating point queue is loaded by launching instructions.
+It is emptied normally when the floating point completes all
+outstanding instructions and by floating point exception
+handlers with the store double floating point queue (stdfq)
+instruction.
+
+Special Registers
+~~~~~~~~~~~~~~~~~
+
+The SPARC architecture includes two special registers
+which are critical to the programming model: the Processor State
+Register (psr) and the Window Invalid Mask (wim).  The psr
+contains the condition codes, processor interrupt level, trap
+enable bit, supervisor mode and previous supervisor mode bits,
+version information, floating point unit and coprocessor enable
+bits, and the current window pointer (cwp).  The cwp field of
+the psr and wim register are used to manage the register windows
+in the SPARC architecture.  The register windows are discussed
+in more detail below.
+
+Register Windows
+----------------
+
+The SPARC architecture includes the concept of
+register windows.  An overly simplistic way to think of these
+windows is to imagine them as being an infinite supply of
+"fresh" register sets available for each subroutine to use.  In
+reality, they are much more complicated.
+
+The save instruction is used to obtain a new register
+window.  This instruction decrements the current window pointer,
+thus providing a new set of registers for use.  This register
+set includes eight fresh local registers for use exclusively by
+this subroutine.  When done with a register set, the restore
+instruction increments the current window pointer and the
+previous register set is once again available.
+
+The two primary issues complicating the use of
+register windows are that (1) the set of register windows is
+finite, and (2) some registers are shared between adjacent
+registers windows.
+
+Because the set of register windows is finite, it is
+possible to execute enough save instructions without
+corresponding restoreâs to consume all of the register windows.
+This is easily accomplished in a high level language because
+each subroutine typically performs a save instruction upon
+entry.  Thus having a subroutine call depth greater than the
+number of register windows will result in a window overflow
+condition.  The window overflow condition generates a trap which
+must be handled in software.  The window overflow trap handler
+is responsible for saving the contents of the oldest register
+window on the program stack.
+
+Similarly, the subroutines will eventually complete
+and begin to perform restoreâs.  If the restore results in the
+need for a register window which has previously been written to
+memory as part of an overflow, then a window underflow condition
+results.  Just like the window overflow, the window underflow
+condition must be handled in software by a trap handler.  The
+window underflow trap handler is responsible for reloading the
+contents of the register window requested by the restore
+instruction from the program stack.
+
+The Window Invalid Mask (wim) and the Current Window
+Pointer (cwp) field in the psr are used in conjunction to manage
+the finite set of register windows and detect the window
+overflow and underflow conditions.  The cwp contains the index
+of the register window currently in use.  The save instruction
+decrements the cwp modulo the number of register windows.
+Similarly, the restore instruction increments the cwp modulo the
+number of register windows.  Each bit in the  wim represents
+represents whether a register window contains valid information.
+The value of 0 indicates the register window is valid and 1
+indicates it is invalid.  When a save instruction causes the cwp
+to point to a register window which is marked as invalid, a
+window overflow condition results.  Conversely, the restore
+instruction may result in a window underflow condition.
+
+Other than the assumption that a register window is
+always available for trap (i.e. interrupt) handlers, the SPARC
+architecture places no limits on the number of register windows
+simultaneously marked as invalid (i.e. number of bits set in the
+wim).  However, RTEMS assumes that only one register window is
+marked invalid at a time (i.e. only one bit set in the wim).
+This makes the maximum possible number of register windows
+available to the user while still meeting the requirement that
+window overflow and underflow conditions can be detected.
+
+The window overflow and window underflow trap
+handlers are a critical part of the run-time environment for a
+SPARC application.  The SPARC architectural specification allows
+for the number of register windows to be any power of two less
+than or equal to 32.  The most common choice for SPARC
+implementations appears to be 8 register windows.  This results
+in the cwp ranging in value from 0 to 7 on most implementations.
+
+The second complicating factor is the sharing of
+registers between adjacent register windows.  While each
+register window has its own set of local registers, the input
+and output registers are shared between adjacent windows.  The
+output registers for register window N are the same as the input
+registers for register window ((N - 1) modulo RW) where RW is
+the number of register windows.  An alternative way to think of
+this is to remember how parameters are passed to a subroutine on
+the SPARC.  The caller loads values into what are its output
+registers.  Then after the callee executes a save instruction,
+those parameters are available in its input registers.  This is
+a very efficient way to pass parameters as no data is actually
+moved by the save or restore instructions.
+
+Call and Return Mechanism
+-------------------------
+
+The SPARC architecture supports a simple yet
+effective call and return mechanism.  A subroutine is invoked
+via the call (call) instruction.  This instruction places the
+return address in the callerâs output register 7 (o7).  After
+the callee executes a save instruction, this value is available
+in input register 7 (i7) until the corresponding restore
+instruction is executed.
+
+The callee returns to the caller via a jmp to the
+return address.  There is a delay slot following this
+instruction which is commonly used to execute a restore
+instruction â if a register window was allocated by this
+subroutine.
+
+It is important to note that the SPARC subroutine
+call and return mechanism does not automatically save and
+restore any registers.  This is accomplished via the save and
+restore instructions which manage the set of registers windows.
+
+In case a floating-point unit is supported, then floating-point return values
+appear in the floating-point registers.  Single-precision values occupy %f0;
+double-precision values occupy %f0 and %f1.  Otherwise, these are scratch
+registers.  Due to this the hardware and software floating-point ABIs are
+incompatible.
+
+Calling Mechanism
+-----------------
+
+All RTEMS directives are invoked using the regular
+SPARC calling convention via the call instruction.
+
+Register Usage
+--------------
+
+As discussed above, the call instruction does not
+automatically save any registers.  The save and restore
+instructions are used to allocate and deallocate register
+windows.  When a register window is allocated, the new set of
+local registers are available for the exclusive use of the
+subroutine which allocated this register set.
+
+Parameter Passing
+-----------------
+
+RTEMS assumes that arguments are placed in the
+callerâs output registers with the first argument in output
+register 0 (o0), the second argument in output register 1 (o1),
+and so forth.  Until the callee executes a save instruction, the
+parameters are still visible in the output registers.  After the
+callee executes a save instruction, the parameters are visible
+in the corresponding input registers.  The following pseudo-code
+illustrates the typical sequence used to call a RTEMS directive
+with three (3) arguments:
+.. code:: c
+
+    load third argument into o2
+    load second argument into o1
+    load first argument into o0
+    invoke directive
+
+User-Provided Routines
+----------------------
+
+All user-provided routines invoked by RTEMS, such as
+user extensions, device drivers, and MPCI routines, must also
+adhere to these calling conventions.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Memory Model
+============
+
+A processor may support any combination of memory
+models ranging from pure physical addressing to complex demand
+paged virtual memory systems.  RTEMS supports a flat memory
+model which ranges contiguously over the processorâs allowable
+address space.  RTEMS does not support segmentation or virtual
+memory of any kind.  The appropriate memory model for RTEMS
+provided by the targeted processor and related characteristics
+of that model are described in this chapter.
+
+Flat Memory Model
+-----------------
+
+The SPARC architecture supports a flat 32-bit address
+space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4
+gigabytes).  Each address is represented by a 32-bit value and
+is byte addressable.  The address may be used to reference a
+single byte, half-word (2-bytes), word (4 bytes), or doubleword
+(8 bytes).  Memory accesses within this address space are
+performed in big endian fashion by the SPARC.  Memory accesses
+which are not properly aligned generate a "memory address not
+aligned" trap (type number 7).  The following table lists the
+alignment requirements for a variety of data accesses:
+
+.. code:: c
+
+    +--------------+-----------------------+
+    |   Data Type  | Alignment Requirement |
+    +--------------+-----------------------+
+    |     byte     |          1            |
+    |   half-word  |          2            |
+    |     word     |          4            |
+    |  doubleword  |          8            |
+    +--------------+-----------------------+
+
+Doubleword load and store operations must use a pair
+of registers as their source or destination.  This pair of
+registers must be an adjacent pair of registers with the first
+of the pair being even numbered.  For example, a valid
+destination for a doubleword load might be input registers 0 and
+1 (i0 and i1).  The pair i1 and i2 would be invalid.  \[NOTE:
+Some assemblers for the SPARC do not generate an error if an odd
+numbered register is specified as the beginning register of the
+pair.  In this case, the assembler assumes that what the
+programmer meant was to use the even-odd pair which ends at the
+specified register.  This may or may not have been a correct
+assumption.]
+
+RTEMS does not support any SPARC Memory Management
+Units, therefore, virtual memory or segmentation systems
+involving the SPARC are not supported.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Interrupt Processing
+====================
+
+Different types of processors respond to the
+occurrence of an interrupt in its own unique fashion. In
+addition, each processor type provides a control mechanism to
+allow for the proper handling of an interrupt.  The processor
+dependent response to the interrupt modifies the current
+execution state and results in a change in the execution stream.
+Most processors require that an interrupt handler utilize some
+special control mechanisms to return to the normal processing
+stream.  Although RTEMS hides many of the processor dependent
+details of interrupt processing, it is important to understand
+how the RTEMS interrupt manager is mapped onto the processorâs
+unique architecture. Discussed in this chapter are the SPARCâs
+interrupt response and control mechanisms as they pertain to
+RTEMS.
+
+RTEMS and associated documentation uses the terms
+interrupt and vector.  In the SPARC architecture, these terms
+correspond to traps and trap type, respectively.  The terms will
+be used interchangeably in this manual.
+
+Synchronous Versus Asynchronous Traps
+-------------------------------------
+
+The SPARC architecture includes two classes of traps:
+synchronous and asynchronous.  Asynchronous traps occur when an
+external event interrupts the processor.  These traps are not
+associated with any instruction executed by the processor and
+logically occur between instructions.  The instruction currently
+in the execute stage of the processor is allowed to complete
+although subsequent instructions are annulled.  The return
+address reported by the processor for asynchronous traps is the
+pair of instructions following the current instruction.
+
+Synchronous traps are caused by the actions of an
+instruction.  The trap stimulus in this case either occurs
+internally to the processor or is from an external signal that
+was provoked by the instruction.  These traps are taken
+immediately and the instruction that caused the trap is aborted
+before any state changes occur in the processor itself.   The
+return address reported by the processor for synchronous traps
+is the instruction which caused the trap and the following
+instruction.
+
+Vectoring of Interrupt Handler
+------------------------------
+
+Upon receipt of an interrupt the SPARC automatically
+performs the following actions:
+
+- disables traps (sets the ET bit of the psr to 0),
+
+- the S bit of the psr is copied into the Previous
+  Supervisor Mode (PS) bit of the psr,
+
+- the cwp is decremented by one (modulo the number of
+  register windows) to activate a trap window,
+
+- the PC and nPC are loaded into local register 1 and 2
+  (l0 and l1),
+
+- the trap type (tt) field of the Trap Base Register (TBR)
+  is set to the appropriate value, and
+
+- if the trap is not a reset, then the PC is written with
+  the contents of the TBR and the nPC is written with TBR + 4.  If
+  the trap is a reset, then the PC is set to zero and the nPC is
+  set to 4.
+
+Trap processing on the SPARC has two features which
+are noticeably different than interrupt processing on other
+architectures.  First, the value of psr register in effect
+immediately before the trap occurred is not explicitly saved.
+Instead only reversible alterations are made to it.  Second, the
+Processor Interrupt Level (pil) is not set to correspond to that
+of the interrupt being processed.  When a trap occurs, ALL
+subsequent traps are disabled.  In order to safely invoke a
+subroutine during trap handling, traps must be enabled to allow
+for the possibility of register window overflow and underflow
+traps.
+
+If the interrupt handler was installed as an RTEMS
+interrupt handler, then upon receipt of the interrupt, the
+processor passes control to the RTEMS interrupt handler which
+performs the following actions:
+
+- saves the state of the interrupted task on itâs stack,
+
+- insures that a register window is available for
+  subsequent traps,
+
+- if this is the outermost (i.e. non-nested) interrupt,
+  then the RTEMS interrupt handler switches from the current stack
+  to the interrupt stack,
+
+- enables traps,
+
+- invokes the vectors to a user interrupt service routine (ISR).
+
+Asynchronous interrupts are ignored while traps are
+disabled.  Synchronous traps which occur while traps are
+disabled result in the CPU being forced into an error mode.
+
+A nested interrupt is processed similarly with the
+exception that the current stack need not be switched to the
+interrupt stack.
+
+Traps and Register Windows
+--------------------------
+
+One of the register windows must be reserved at all
+times for trap processing.  This is critical to the proper
+operation of the trap mechanism in the SPARC architecture.  It
+is the responsibility of the trap handler to insure that there
+is a register window available for a subsequent trap before
+re-enabling traps.  It is likely that any high level language
+routines invoked by the trap handler (such as a user-provided
+RTEMS interrupt handler) will allocate a new register window.
+The save operation could result in a window overflow trap.  This
+trap cannot be correctly processed unless (1) traps are enabled
+and (2) a register window is reserved for traps.  Thus, the
+RTEMS interrupt handler insures that a register window is
+available for subsequent traps before enabling traps and
+invoking the userâs interrupt handler.
+
+Interrupt Levels
+----------------
+
+Sixteen levels (0-15) of interrupt priorities are
+supported by the SPARC architecture with level fifteen (15)
+being the highest priority.  Level zero (0) indicates that
+interrupts are fully enabled.  Interrupt requests for interrupts
+with priorities less than or equal to the current interrupt mask
+level are ignored. Level fifteen (15) is a non-maskable interrupt
+(NMI), which makes it unsuitable for standard usage since it can
+affect the real-time behaviour by interrupting critical sections
+and spinlocks. Disabling traps stops also the NMI interrupt from
+happening. It can however be used for power-down or other
+critical events.
+
+Although RTEMS supports 256 interrupt levels, the
+SPARC only supports sixteen.  RTEMS interrupt levels 0 through
+15 directly correspond to SPARC processor interrupt levels.  All
+other RTEMS interrupt levels are undefined and their behavior is
+unpredictable.
+
+Many LEON SPARC v7/v8 systems features an extended interrupt controller
+which adds an extra step of interrupt decoding to allow handling of
+interrupt 16-31. When such an extended interrupt is generated the CPU
+traps into a specific interrupt trap level 1-14 and software reads out from
+the interrupt controller which extended interrupt source actually caused the
+interrupt.
+
+Disabling of Interrupts by RTEMS
+--------------------------------
+
+During the execution of directive calls, critical
+sections of code may be executed.  When these sections are
+encountered, RTEMS disables interrupts to level fifteen (15)
+before the execution of the section and restores them to the
+previous level upon completion of the section.  RTEMS has been
+optimized to ensure that interrupts are disabled for less than
+RTEMS_MAXIMUM_DISABLE_PERIOD microseconds on a RTEMS_MAXIMUM_DISABLE_PERIOD_MHZ
+Mhz ERC32 with zero wait states.
+These numbers will vary based the number of wait states and
+processor speed present on the target board.
+\[NOTE:  The maximum period with interrupts disabled is hand calculated.  This
+calculation was last performed for Release
+RTEMS_RELEASE_FOR_MAXIMUM_DISABLE_PERIOD.]
+
+[NOTE: It is thought that the length of time at which
+the processor interrupt level is elevated to fifteen by RTEMS is
+not anywhere near as long as the length of time ALL traps are
+disabled as part of the "flush all register windows" operation.]
+
+Non-maskable interrupts (NMI) cannot be disabled, and
+ISRs which execute at this level MUST NEVER issue RTEMS system
+calls.  If a directive is invoked, unpredictable results may
+occur due to the inability of RTEMS to protect its critical
+sections.  However, ISRs that make no system calls may safely
+execute as non-maskable interrupts.
+
+Interrupts are disabled or enabled by performing a system call
+to the Operating System reserved software traps 9
+(SPARC_SWTRAP_IRQDIS) or 10 (SPARC_SWTRAP_IRQDIS). The trap is
+generated by the software trap (Ticc) instruction or indirectly
+by calling sparc_disable_interrupts() or sparc_enable_interrupts()
+functions. Disabling interrupts return the previous interrupt level
+(on trap entry) in register G1 and sets PSR.PIL to 15 to disable
+all maskable interrupts. The interrupt level can be restored by
+trapping into the enable interrupt handler with G1 containing the
+new interrupt level.
+
+Interrupt Stack
+---------------
+
+The SPARC architecture does not provide for a
+dedicated interrupt stack.  Thus by default, trap handlers would
+execute on the stack of the RTEMS task which they interrupted.
+This artificially inflates the stack requirements for each task
+since EVERY task stack would have to include enough space to
+account for the worst case interrupt stack requirements in
+addition to itâs own worst case usage.  RTEMS addresses this
+problem on the SPARC by providing a dedicated interrupt stack
+managed by software.
+
+During system initialization, RTEMS allocates the
+interrupt stack from the Workspace Area.  The amount of memory
+allocated for the interrupt stack is determined by the
+interrupt_stack_size field in the CPU Configuration Table.  As
+part of processing a non-nested interrupt, RTEMS will switch to
+the interrupt stack before invoking the installed handler.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Default Fatal Error Processing
+==============================
+
+Upon detection of a fatal error by either the
+application or RTEMS the fatal error manager is invoked.  The
+fatal error manager will invoke the user-supplied fatal error
+handlers.  If no user-supplied handlers are configured,  the
+RTEMS provided default fatal error handler is invoked.  If the
+user-supplied fatal error handlers return to the executive the
+default fatal error handler is then invoked.  This chapter
+describes the precise operations of the default fatal error
+handler.
+
+Default Fatal Error Handler Operations
+--------------------------------------
+
+The default fatal error handler which is invoked by
+the fatal_error_occurred directive when there is no user handler
+configured or the user handler returns control to RTEMS.
+
+If the BSP has been configured with ``BSP_POWER_DOWN_AT_FATAL_HALT``
+set to true, the default handler will disable interrupts
+and enter power down mode. If power down mode is not available,
+it goes into an infinite loop to simulate a halt processor instruction.
+
+If ``BSP_POWER_DOWN_AT_FATAL_HALT`` is set to false, the default
+handler will place the value ``1`` in register ``g1``, the
+error source in register ``g2``, and the error code in register``g3``. It will then generate a system error which will
+hand over control to the debugger, simulator, etc.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is supported.  Available platforms are the Cobham Gaisler GR712RC and
+GR740.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is supported.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Board Support Packages
+======================
+
+An RTEMS Board Support Package (BSP) must be designed
+to support a particular processor and target board combination.
+This chapter presents a discussion of SPARC specific BSP issues.
+For more information on developing a BSP, refer to the chapter
+titled Board Support Packages in the RTEMS
+Applications Userâs Guide.
+
+System Reset
+------------
+
+An RTEMS based application is initiated or
+re-initiated when the SPARC processor is reset.  When the SPARC
+is reset, the processor performs the following actions:
+
+- the enable trap (ET) of the psr is set to 0 to disable
+  traps,
+
+- the supervisor bit (S) of the psr is set to 1 to enter
+  supervisor mode, and
+
+- the PC is set 0 and the nPC is set to 4.
+
+The processor then begins to execute the code at
+location 0.  It is important to note that all fields in the psr
+are not explicitly set by the above steps and all other
+registers retain their value from the previous execution mode.
+This is true even of the Trap Base Register (TBR) whose contents
+reflect the last trap which occurred before the reset.
+
+Processor Initialization
+------------------------
+
+It is the responsibility of the applicationâs
+initialization code to initialize the TBR and install trap
+handlers for at least the register window overflow and register
+window underflow conditions.  Traps should be enabled before
+invoking any subroutines to allow for register window
+management.  However, interrupts should be disabled by setting
+the Processor Interrupt Level (pil) field of the psr to 15.
+RTEMS installs itâs own Trap Table as part of initialization
+which is initialized with the contents of the Trap Table in
+place when the ``rtems_initialize_executive`` directive was invoked.
+Upon completion of executive initialization, interrupts are
+enabled.
+
+If this SPARC implementation supports on-chip caching
+and this is to be utilized, then it should be enabled during the
+reset application initialization code.
+
+In addition to the requirements described in the
+Board Support Packages chapter of the C
+Applications Users Manual for the reset code
+which is executed before the call to``rtems_initialize_executive``, the SPARC version has the following
+specific requirements:
+
+- Must leave the S bit of the status register set so that
+  the SPARC remains in the supervisor state.
+
+- Must set stack pointer (sp) such that a minimum stack
+  size of MINIMUM_STACK_SIZE bytes is provided for the``rtems_initialize_executive`` directive.
+
+- Must disable all external interrupts (i.e. set the pil
+  to 15).
+
+- Must enable traps so window overflow and underflow
+  conditions can be properly handled.
+
+- Must initialize the SPARCâs initial trap table with at
+  least trap handlers for register window overflow and register
+  window underflow.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+SPARC-64 Specific Information
+#############################
+
+This document discusses the SPARC Version 9 (aka SPARC-64, SPARC64 or SPARC V9)
+architecture dependencies in this port of RTEMS.
+
+The SPARC V9 architecture leaves a lot of undefined implemenation dependencies
+which are defined by the processor models. Consult the specific CPU model
+section in this document for additional documents covering the implementation
+dependent architectural features.
+
+**sun4u Specific Information**
+
+sun4u is the subset of the SPARC V9 implementations comprising the UltraSPARC I
+through UltraSPARC IV processors.
+
+The following documents were used in developing the SPARC-64 sun4u port:
+
+- UltraSPARC  UserÃ¢ÂÂs Manual
+  (http://www.sun.com/microelectronics/manuals/ultrasparc/802-7220-02.pdf)
+
+- UltraSPARC IIIi Processor (datasheets.chipdb.org/Sun/UltraSparc-IIIi.pdf)
+
+**sun4v Specific Information**
+
+sun4v is the subset of the SPARC V9 implementations comprising the
+UltraSPARC T1 or T2 processors.
+
+The following documents were used in developing the SPARC-64 sun4v port:
+
+- UltraSPARC Architecture 2005 Specification
+  (http://opensparc-t1.sunsource.net/specs/UA2005-current-draft-P-EXT.pdf)
+
+- UltraSPARC T1 supplement to UltraSPARC Architecture 2005 Specification
+  (http://opensparc-t1.sunsource.net/specs/UST1-UASuppl-current-draft-P-EXT.pdf)
+
+The defining feature that separates the sun4v architecture from its
+predecessor is the existence of a super-privileged hypervisor that
+is responsible for providing virtualized execution environments.  The impact
+of the hypervisor on the real-time guarantees available with sun4v has not
+yet been determined.
+
+CPU Model Dependent Features
+============================
+
+CPU Model Feature Flags
+-----------------------
+
+This section presents the set of features which vary across
+SPARC-64 implementations and
+are of importance to RTEMS. The set of CPU model feature macros
+are defined in the file
+cpukit/score/cpu/sparc64/sparc64.h based upon the particular
+CPU model defined on the compilation command line.
+
+CPU Model Name
+~~~~~~~~~~~~~~
+
+The macro CPU MODEL NAME is a string which designates
+the name of this CPU model.
+For example, for the UltraSPARC T1 SPARC V9 model,
+this macro is set to the string "sun4v".
+
+Floating Point Unit
+~~~~~~~~~~~~~~~~~~~
+
+The macro SPARC_HAS_FPU is set to 1 to indicate that
+this CPU model has a hardware floating point unit and 0
+otherwise.
+
+Number of Register Windows
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The macro SPARC_NUMBER_OF_REGISTER_WINDOWS is set to
+indicate the number of register window sets implemented by this
+CPU model.  The SPARC architecture allows for a maximum of
+thirty-two register window sets although most implementations
+only include eight.
+
+CPU Model Implementation Notes
+------------------------------
+
+This section describes the implemenation dependencies of the
+CPU Models sun4u and sun4v of the SPARC V9 architecture.
+
+sun4u Notes
+~~~~~~~~~~~
+
+XXX
+
+sun4v Notes
+-----------
+
+XXX
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Calling Conventions
+===================
+
+Each high-level language compiler generates
+subroutine entry and exit code based upon a set of rules known
+as the compilerâs calling convention.   These rules address the
+following issues:
+
+- register preservation and usage
+
+- parameter passing
+
+- call and return mechanism
+
+A compilerâs calling convention is of importance when
+interfacing to subroutines written in another language either
+assembly or high-level.  Even when the high-level language and
+target processor are the same, different compilers may use
+different calling conventions.  As a result, calling conventions
+are both processor and compiler dependent.
+
+The following document also provides some conventions on the
+global register usage in SPARC V9:
+http://developers.sun.com/solaris/articles/sparcv9abi.html
+
+Programming Model
+-----------------
+
+This section discusses the programming model for the
+SPARC architecture.
+
+Non-Floating Point Registers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The SPARC architecture defines thirty-two
+non-floating point registers directly visible to the programmer.
+These are divided into four sets:
+
+- input registers
+
+- local registers
+
+- output registers
+
+- global registers
+
+Each register is referred to by either two or three
+names in the SPARC reference manuals.  First, the registers are
+referred to as r0 through r31 or with the alternate notation
+r[0] through r[31].  Second, each register is a member of one of
+the four sets listed above.  Finally, some registers have an
+architecturally defined role in the programming model which
+provides an alternate name.  The following table describes the
+mapping between the 32 registers and the register sets:
+
+.. code:: c
+
+    +-----------------+----------------+------------------+
+    | Register Number | Register Names |   Description    |
+    +-----------------+----------------+------------------+
+    |     0 - 7       |    g0 - g7     | Global Registers |
+    +-----------------+----------------+------------------+
+    |     8 - 15      |    o0 - o7     | Output Registers |
+    +-----------------+----------------+------------------+
+    |    16 - 23      |    l0 - l7     | Local Registers  |
+    +-----------------+----------------+------------------+
+    |    24 - 31      |    i0 - i7     | Input Registers  |
+    +-----------------+----------------+------------------+
+
+As mentioned above, some of the registers serve
+defined roles in the programming model.  The following table
+describes the role of each of these registers:
+
+.. code:: c
+
+    +---------------+----------------+----------------------+
+    | Register Name | Alternate Name |      Description     |
+    +---------------+----------------+----------------------+
+    |     g0        |      na        |    reads return 0    |
+    |               |                |  writes are ignored  |
+    +---------------+----------------+----------------------+
+    |     o6        |      sp        |     stack pointer    |
+    +---------------+----------------+----------------------+
+    |     i6        |      fp        |     frame pointer    |
+    +---------------+----------------+----------------------+
+    |     i7        |      na        |    return address    |
+    +---------------+----------------+----------------------+
+
+Floating Point Registers
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+The SPARC V9 architecture includes sixty-four,
+thirty-two bit registers.  These registers may be viewed as
+follows:
+
+- 32 32-bit single precision floating point or integer registers
+  (f0, f1,  ... f31)
+
+- 32 64-bit double precision floating point registers (f0, f2,
+  f4, ... f62)
+
+- 16 128-bit extended precision floating point registers (f0, f4,
+  f8, ... f60)
+
+The floating point state register (fsr) specifies
+the behavior of the floating point unit for rounding, contains
+its condition codes, version specification, and trap information.
+
+Special Registers
+~~~~~~~~~~~~~~~~~
+
+The SPARC architecture includes a number of special registers:
+
+*``Ancillary State Registers (ASRs)``*
+    The ancillary state registers (ASRs) are optional state registers that
+    may be privileged or nonprivileged. ASRs 16-31 are implementation-
+    dependent. The SPARC V9 ASRs include: y, ccr, asi, tick, pc, fprs.
+    The sun4u ASRs include: pcr, pic, dcr, gsr, softint set, softint clr,
+    softint, and tick cmpr. The sun4v ASRs include: pcr, pic, gsr, soft-
+    int set, softint clr, softint, tick cmpr, stick, and stick cmpr.
+
+*``Processor State Register (pstate)``*
+    The privileged pstate register contains control fields for the proces-
+    sorÃ¢ÂÂs current state. Its flag fields include the interrupt enable, privi-
+    leged mode, and enable FPU.
+
+*``Processor Interrupt Level (pil)``*
+    The PIL specifies the interrupt level above which interrupts will be
+    accepted.
+
+*``Trap Registers``*
+    The trap handling mechanism of the SPARC V9 includes a number of
+    registers, including: trap program counter (tpc), trap next pc (tnpc),
+    trap state (tstate), trap type (tt), trap base address (tba), and trap
+    level (tl).
+
+*``Alternate Globals``*
+    The AG bit of the pstate register provides access to an alternate set
+    of global registers. On sun4v, the AG bit is replaced by the global
+    level (gl) register, providing access to at least two and at most eight
+    alternate sets of globals.
+
+*``Register Window registers``*
+    A number of registers assist in register window management.
+    These include the current window pointer (cwp), savable windows
+    (cansave), restorable windows (canrestore), clean windows (clean-
+    win), other windows (otherwin), and window state (wstate).
+
+Register Windows
+----------------
+
+The SPARC architecture includes the concept of
+register windows.  An overly simplistic way to think of these
+windows is to imagine them as being an infinite supply of
+"fresh" register sets available for each subroutine to use.  In
+reality, they are much more complicated.
+
+The save instruction is used to obtain a new register window.
+This instruction increments the current window pointer, thus
+providing a new set of registers for use. This register set
+includes eight fresh local registers for use exclusively by
+this subroutine. When done with a register set, the restore
+instruction decrements the current window pointer and the
+previous register set is once again available.
+
+The two primary issues complicating the use of register windows
+are that (1) the set of register windows is finite, and (2) some
+registers are shared between adjacent registers windows.
+
+Because the set of register windows is finite, it is
+possible to execute enough save instructions without
+corresponding restoreâs to consume all of the register windows.
+This is easily accomplished in a high level language because
+each subroutine typically performs a save instruction upon
+entry.  Thus having a subroutine call depth greater than the
+number of register windows will result in a window overflow
+condition.  The window overflow condition generates a trap which
+must be handled in software.  The window overflow trap handler
+is responsible for saving the contents of the oldest register
+window on the program stack.
+
+Similarly, the subroutines will eventually complete
+and begin to perform restoreâs.  If the restore results in the
+need for a register window which has previously been written to
+memory as part of an overflow, then a window underflow condition
+results.  Just like the window overflow, the window underflow
+condition must be handled in software by a trap handler.  The
+window underflow trap handler is responsible for reloading the
+contents of the register window requested by the restore
+instruction from the program stack.
+
+The cansave, canrestore, otherwin, and cwp are used in conjunction
+to manage the finite set of register windows and detect the window
+overflow and underflow conditions. The first three of these
+registers must satisfy the invariant cansave + canrestore + otherwin =
+nwindow - 2, where nwindow is the number of register windows.
+The cwp contains the index of the register window currently in use.
+RTEMS does not use the cleanwin and otherwin registers.
+
+The save instruction increments the cwp modulo the number of
+register windows, and if cansave is 0 then it also generates a
+window overflow. Similarly, the restore instruction decrements the
+cwp modulo the number of register windows, and if canrestore is 0 then it
+also generates a window underflow.
+
+Unlike with the SPARC model, the SPARC-64 port does not assume that
+a register window is available for a trap. The window overflow
+and underflow conditions are not detected without hardware generating
+the trap. (These conditions can be detected by reading the register window
+registers and doing some simple arithmetic.)
+
+The window overflow and window underflow trap
+handlers are a critical part of the run-time environment for a
+SPARC application.  The SPARC architectural specification allows
+for the number of register windows to be any power of two less
+than or equal to 32.  The most common choice for SPARC
+implementations appears to be 8 register windows.  This results
+in the cwp ranging in value from 0 to 7 on most implementations.
+
+The second complicating factor is the sharing of
+registers between adjacent register windows.  While each
+register window has its own set of local registers, the input
+and output registers are shared between adjacent windows.  The
+output registers for register window N are the same as the input
+registers for register window ((N + 1) modulo RW) where RW is
+the number of register windows.  An alternative way to think of
+this is to remember how parameters are passed to a subroutine on
+the SPARC.  The caller loads values into what are its output
+registers.  Then after the callee executes a save instruction,
+those parameters are available in its input registers.  This is
+a very efficient way to pass parameters as no data is actually
+moved by the save or restore instructions.
+
+Call and Return Mechanism
+-------------------------
+
+The SPARC architecture supports a simple yet
+effective call and return mechanism.  A subroutine is invoked
+via the call (call) instruction.  This instruction places the
+return address in the callerâs output register 7 (o7).  After
+the callee executes a save instruction, this value is available
+in input register 7 (i7) until the corresponding restore
+instruction is executed.
+
+The callee returns to the caller via a jmp to the
+return address.  There is a delay slot following this
+instruction which is commonly used to execute a restore
+instruction â if a register window was allocated by this
+subroutine.
+
+It is important to note that the SPARC subroutine
+call and return mechanism does not automatically save and
+restore any registers.  This is accomplished via the save and
+restore instructions which manage the set of registers windows.
+This allows for the compiler to generate leaf-optimized functions
+that utilize the callerÃ¢ÂÂs output registers without using save and restore.
+
+Calling Mechanism
+-----------------
+
+All RTEMS directives are invoked using the regular
+SPARC calling convention via the call instruction.
+
+Register Usage
+--------------
+
+As discussed above, the call instruction does not
+automatically save any registers.  The save and restore
+instructions are used to allocate and deallocate register
+windows.  When a register window is allocated, the new set of
+local registers are available for the exclusive use of the
+subroutine which allocated this register set.
+
+Parameter Passing
+-----------------
+
+RTEMS assumes that arguments are placed in the
+callerâs output registers with the first argument in output
+register 0 (o0), the second argument in output register 1 (o1),
+and so forth.  Until the callee executes a save instruction, the
+parameters are still visible in the output registers.  After the
+callee executes a save instruction, the parameters are visible
+in the corresponding input registers.  The following pseudo-code
+illustrates the typical sequence used to call a RTEMS directive
+with three (3) arguments:
+.. code:: c
+
+    load third argument into o2
+    load second argument into o1
+    load first argument into o0
+    invoke directive
+
+User-Provided Routines
+----------------------
+
+All user-provided routines invoked by RTEMS, such as
+user extensions, device drivers, and MPCI routines, must also
+adhere to these calling conventions.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Memory Model
+============
+
+A processor may support any combination of memory
+models ranging from pure physical addressing to complex demand
+paged virtual memory systems.  RTEMS supports a flat memory
+model which ranges contiguously over the processorâs allowable
+address space.  RTEMS does not support segmentation or virtual
+memory of any kind.  The appropriate memory model for RTEMS
+provided by the targeted processor and related characteristics
+of that model are described in this chapter.
+
+Flat Memory Model
+-----------------
+
+The SPARC-64 architecture supports a flat 64-bit address space with
+addresses ranging from 0x0000000000000000 to 0xFFFFFFFFFFFFFFFF.
+Each address is represented by a 64-bit value (and an 8-bit address
+space identifider or ASI) and is byte addressable. The address
+may be used to reference a single byte, half-word (2-bytes),
+word (4 bytes), doubleword (8 bytes), or quad-word (16 bytes).
+Memory accesses within this address space are performed
+in big endian fashion by the SPARC. Memory accesses which are not
+properly aligned generate a "memory address not aligned" trap
+(type number 0x34). The following table lists the alignment
+requirements for a variety of data accesses:
+
+.. code:: c
+
+    +--------------+-----------------------+
+    |   Data Type  | Alignment Requirement |
+    +--------------+-----------------------+
+    |     byte     |          1            |
+    |   half-word  |          2            |
+    |     word     |          4            |
+    |  doubleword  |          8            |
+    |   quadword   |          16           |
+    +--------------+-----------------------+
+
+RTEMS currently does not support any SPARC Memory Management
+Units, therefore, virtual memory or segmentation systems
+involving the SPARC are not supported.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Interrupt Processing
+====================
+
+RTEMS and associated documentation uses the terms
+interrupt and vector.  In the SPARC architecture, these terms
+correspond to traps and trap type, respectively.  The terms will
+be used interchangeably in this manual. Note that in the SPARC manuals,
+interrupts are a subset of the traps that are delivered to software
+interrupt handlers.
+
+Synchronous Versus Asynchronous Traps
+-------------------------------------
+
+The SPARC architecture includes two classes of traps:
+synchronous (precise) and asynchronous (deferred).
+Asynchronous traps occur when an
+external event interrupts the processor.  These traps are not
+associated with any instruction executed by the processor and
+logically occur between instructions.  The instruction currently
+in the execute stage of the processor is allowed to complete
+although subsequent instructions are annulled.  The return
+address reported by the processor for asynchronous traps is the
+pair of instructions following the current instruction.
+
+Synchronous traps are caused by the actions of an
+instruction.  The trap stimulus in this case either occurs
+internally to the processor or is from an external signal that
+was provoked by the instruction.  These traps are taken
+immediately and the instruction that caused the trap is aborted
+before any state changes occur in the processor itself.   The
+return address reported by the processor for synchronous traps
+is the instruction which caused the trap and the following
+instruction.
+
+Vectoring of Interrupt Handler
+------------------------------
+
+Upon receipt of an interrupt the SPARC automatically
+performs the following actions:
+
+- The trap level is set. This provides access to a fresh set of
+  privileged trap-state registers used to save the current state,
+  in effect, pushing a frame on the trap stack.
+  TL <- TL + 1
+
+- Existing state is preserved
+  - TSTATE[TL].CCR <- CCR
+  - TSTATE[TL].ASI <- ASI
+  - TSTATE[TL].PSTATE <- PSTATE
+  - TSTATE[TL].CWP <- CWP
+  - TPC[TL] <- PC
+  - TNPC[TL] <- nPC
+
+- The trap type is preserved. TT[TL] <- the trap type
+
+- The PSTATE register is updated to a predefined state
+  - PSTATE.MM is unchanged
+  - PSTATE.RED <- 0
+  - PSTATE.PEF <- 1 if FPU is present, 0 otherwise
+  - PSTATE.AM <- 0 (address masking is turned off)
+  - PSTATE.PRIV <- 1 (the processor enters privileged mode)
+  - PSTATE.IE <- 0 (interrupts are disabled)
+  - PSTATE.AG <- 1 (global regs are replaced with alternate globals)
+  - PSTATE.CLE <- PSTATE.TLE (set endian mode for traps)
+
+- For a register-window trap only, CWP is set to point to the register
+  window that must be accessed by the trap-handler software, that is:
+
+  - If TT[TL] = 0x24 (a clean window trap), then CWP <- CWP + 1.
+  - If (0x80 <= TT[TL] <= 0xBF) (window spill trap), then CWP <- CWP +
+    CANSAVE + 2.
+  - If (0xC0 <= TT[TL] <= 0xFF) (window fill trap), then CWP <- CWP1.
+  - For non-register-window traps, CWP is not changed.
+
+- Control is transferred into the trap table:
+
+  - PC <- TBA<63:15> (TL>0) TT[TL] 0 0000
+  - nPC <- TBA<63:15> (TL>0) TT[TL] 0 0100
+  - where (TL>0) is 0 if TL = 0, and 1 if TL > 0.
+
+In order to safely invoke a subroutine during trap handling, traps must be
+enabled to allow for the possibility of register window overflow and
+underflow traps.
+
+If the interrupt handler was installed as an RTEMS
+interrupt handler, then upon receipt of the interrupt, the
+processor passes control to the RTEMS interrupt handler which
+performs the following actions:
+
+- saves the state of the interrupted task on itâs stack,
+
+- switches the processor to trap level 0,
+
+- if this is the outermost (i.e. non-nested) interrupt,
+  then the RTEMS interrupt handler switches from the current stack
+  to the interrupt stack,
+
+- enables traps,
+
+- invokes the vectors to a user interrupt service routine (ISR).
+
+Asynchronous interrupts are ignored while traps are
+disabled.  Synchronous traps which occur while traps are
+disabled may result in the CPU being forced into an error mode.
+
+A nested interrupt is processed similarly with the
+exception that the current stack need not be switched to the
+interrupt stack.
+
+Traps and Register Windows
+--------------------------
+
+XXX
+
+Interrupt Levels
+----------------
+
+Sixteen levels (0-15) of interrupt priorities are
+supported by the SPARC architecture with level fifteen (15)
+being the highest priority.  Level zero (0) indicates that
+interrupts are fully enabled.  Interrupt requests for interrupts
+with priorities less than or equal to the current interrupt mask
+level are ignored.
+
+Although RTEMS supports 256 interrupt levels, the
+SPARC only supports sixteen.  RTEMS interrupt levels 0 through
+15 directly correspond to SPARC processor interrupt levels.  All
+other RTEMS interrupt levels are undefined and their behavior is
+unpredictable.
+
+Disabling of Interrupts by RTEMS
+--------------------------------
+
+XXX
+
+Interrupt Stack
+---------------
+
+The SPARC architecture does not provide for a
+dedicated interrupt stack.  Thus by default, trap handlers would
+execute on the stack of the RTEMS task which they interrupted.
+This artificially inflates the stack requirements for each task
+since EVERY task stack would have to include enough space to
+account for the worst case interrupt stack requirements in
+addition to itâs own worst case usage.  RTEMS addresses this
+problem on the SPARC by providing a dedicated interrupt stack
+managed by software.
+
+During system initialization, RTEMS allocates the
+interrupt stack from the Workspace Area.  The amount of memory
+allocated for the interrupt stack is determined by the
+interrupt_stack_size field in the CPU Configuration Table.  As
+part of processing a non-nested interrupt, RTEMS will switch to
+the interrupt stack before invoking the installed handler.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Default Fatal Error Processing
+==============================
+
+Upon detection of a fatal error by either the
+application or RTEMS the fatal error manager is invoked.  The
+fatal error manager will invoke the user-supplied fatal error
+handlers.  If no user-supplied handlers are configured,  the
+RTEMS provided default fatal error handler is invoked.  If the
+user-supplied fatal error handlers return to the executive the
+default fatal error handler is then invoked.  This chapter
+describes the precise operations of the default fatal error
+handler.
+
+Default Fatal Error Handler Operations
+--------------------------------------
+
+The default fatal error handler which is invoked by
+the fatal_error_occurred directive when there is no user handler
+configured or the user handler returns control to RTEMS.  The
+default fatal error handler disables processor interrupts to
+level 15, places the error code in g1, and goes into an infinite
+loop to simulate a halt processor instruction.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is supported.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
+Board Support Packages
+======================
+
+An RTEMS Board Support Package (BSP) must be designed
+to support a particular processor and target board combination.
+This chapter presents a discussion of SPARC specific BSP issues.
+For more information on developing a BSP, refer to the chapter
+titled Board Support Packages in the RTEMS
+Applications Userâs Guide.
+
+HelenOS and Open Firmware
+-------------------------
+
+The provided BSPs make use of some bootstrap and low-level hardware code
+of the HelenOS operating system. These files can be found in the shared/helenos
+directory of the sparc64 bsp directory.  Consult the sources for more
+detailed information.
+
+The shared BSP code also uses the Open Firmware interface to re-use firmware
+code, primarily for console support and default trap handlers.
+
+Command and Variable Index
+##########################
+
+There are currently no Command and Variable Index entries.
+
+.. COMMENT: @printindex fn
+
+Concept Index
+#############
+
+There are currently no Concept Index entries.
+
+.. COMMENT: @printindex cp 
