source: rtems-docs/bsp_howto/bsp_howto_old_reference_only.rst @ 9aafb39

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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 Getting Started (C) Guide

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

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.. COMMENT: Title Page Stuff

.. COMMENT: I don't really like having a short title page.  -joel

.. COMMENT: @shorttitlepage BSP and Device Driver Development Guide

=======================================
BSP and Device Driver Development Guide
=======================================

.. 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 © 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 BSP and Device Driver Development Guide
#############################################

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Introduction
############

Before reading this documentation, it is strongly advised to read the
RTEMS Development Environment Guide to get acquainted with the RTEMS
directory structure.  This document describes how to do a RTEMS Board
Support Package, i.e. how to port RTEMS on a new target board. Discussions
are provided for the following topics:

- RTEMS Board Support Package Organization

- Makefiles and the Linker Command Script

- Board Initialization Sequence

- Device Drivers Including:
  - Console Driver
  - Clock Driver
  - Timer Driver
  - Real-Time Clock Driver
  - Non-Volatile Memory Driver
  - Networking Driver
  - Shared Memory Support Driver
  - Analog Driver
  - Discrete Driver

The original version of this manual was written by Geoffroy Montel
<g_montel@yahoo.com>.  When he started development of the gen68340
BSP, this manual did not exist.  He wrote the initial version of
this manual as the result of his experiences.  At that time, this
document was viewed internally as the most important "missing manual"
in the RTEMS documentation set.

The gen68340 BSP is a good example of the life of an RTEMS BSP.  It is
based upon a part not recommended for new designs and none of the core RTEMS
Project team members have one of these boards.  Thus we are unlikely to
perform major updates on this BSP.  So as long as it compiles and links all
tests, it will be available.

The RTEMS Project team members are always trying to identify common
code across BSPs and refactoring the code into shared routines.
As part of this effort, the we will enhance the common BSP Framework.
Not surprisingly, not every BSP takes advantage of every feature in
the framework.  The gen68340 does not take advantage of as many features
as the ERC32 BSP does.  So in many ways, the ERC32 is a better example
BSP at this point.  But even the ERC32 BSP does not include examples
of every driver template and framework available to the BSP author.
So in this guide we will try to point out good examples from other BSPs.

Our goal is for you to be able to reuse as much code as possible and
write as little board specific code as possible.

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Target Dependent Files
######################

RTEMS has a multi-layered approach to portability.  This is done to
maximize the amount of software that can be reused.  Much of the
RTEMS source code can be reused on all RTEMS platforms.  Other parts
of the executive are specific to hardware in some sense.
RTEMS classifies target dependent code based upon its dependencies
into one of the following categories.

- CPU dependent

- Board dependent

- Peripheral dependent

CPU Dependent
=============

This class of code includes the foundation
routines for the executive proper such as the context switch and
the interrupt subroutine implementations.  Sources for the supported
processor families can be found in ``cpukit/score/cpu``.
A good starting point for a new family of processors is the``no_cpu`` directory, which holds both prototypes and
descriptions of each needed CPU dependent function.

CPU dependent code is further subcategorized if the implementation is
dependent on a particular CPU model.  For example, the MC68000 and MC68020
processors are both members of the m68k CPU family but there are significant
differences between these CPU models which RTEMS must take into account.

The source code found in the ``cpukit/score/cpu`` is required to
only depend upon the CPU model variations that GCC distinguishes
for the purposes of multilib’ing.  Multilib is the term the GNU
community uses to refer to building a single library source multiple
times with different compiler options so the binary code generated
is compatible.  As an example, from GCC’s perspective, many PowerPC
CPU models are just a PPC603e.  Remember that GCC only cares about
the CPU code itself and need not be aware of any peripherals.  In
the embedded community, we are exposed to thousands of CPU models
which are all based upon only a relative small number of CPU cores.

Similarly for the SPARC/ERC32 BSP, the ``RTEMS_CPU`` is specified as``erc32`` which is the name of the CPU model and BSP for this SPARC V7
system on chip.  But the multilib variant used is actually ``v7``
which indicates the ERC32 CPU core is a SPARC V7.

Board Dependent
===============

This class of code provides the most specific glue between RTEMS and
a particular board.  This code is represented by the Board Support Packages
and associated Device Drivers.  Sources for the BSPs included in the
RTEMS distribution are located in the directory ``c/src/lib/libbsp``.
The BSP source directory is further subdivided based on the CPU family
and BSP.

Some BSPs may support multiple board models within a single board family.
This is necessary when the board supports multiple variants on a
single base board.  For example, the Motorola MVME162 board family has a
fairly large number of variations based upon the particular CPU model
and the peripherals actually placed on the board.

Peripheral Dependent
====================

This class of code provides a reusable library of peripheral device
drivers which can be tailored easily to a particular board.  The
libchip library is a collection of reusable software objects that
correspond to standard controllers.  Just as the hardware engineer
chooses a standard controller when designing a board, the goal of
this library is to let the software engineer do the same thing.

The source code for the reusable peripheral driver library may be found
in the directory ``c/src/lib/libchip``.  The source code is further
divided based upon the class of hardware.  Example classes include serial
communications controllers, real-time clocks, non-volatile memory, and
network controllers.

Questions to Ask
================

When evaluating what is required to support RTEMS applications on
a particular target board, the following questions should be asked:

- Does a BSP for this board exist?

- Does a BSP for a similar board exists?

- Is the board’s CPU supported?

If there is already a BSP for the board, then things may already be ready
to start developing application software.  All that remains is to verify
that the existing BSP provides device drivers for all the peripherals
on the board that the application will be using.  For example, the application
in question may require that the board’s Ethernet controller be used and
the existing BSP may not support this.

If the BSP does not exist and the board’s CPU model is supported, then
examine the reusable chip library and existing BSPs for a close match.
Other BSPs and libchip provide starting points for the development
of a new BSP.  It is often possible to copy existing components in
the reusable chip library or device drivers from BSPs from different
CPU families as the starting point for a new device driver.
This will help reduce the development effort required.

If the board’s CPU family is supported but the particular CPU model on
that board is not, then the RTEMS port to that CPU family will have to
be augmented.  After this is done, development of the new BSP can proceed.

Otherwise both CPU dependent code and the BSP will have to be written.

This type of development often requires specialized skills.  If
you need help in making these modifications to RTEMS, please
consider using one of the RTEMS Service Providers.  The current
list of these is at http://www.rtems.org/support.html.

CPU Dependent Executive Files
=============================

The CPU dependent files in the RTEMS executive source code are found
in the following directory:
.. code:: c

    cpukit/score/cpu/*CPU*

where *CPU* is replaced with the CPU family name.

Within each CPU dependent directory inside the executive proper is a
file named ``*CPU*.h`` which contains information about each of the
supported CPU models within that family.

CPU Dependent Support Files
===========================

The CPU dependent support files contain routines which aid in the development
of applications using that CPU family.  For example, the support routines
may contain standard trap handlers for alignment or floating point exceptions
or device drivers for peripheral controllers found on the CPU itself.
This class of code may be found in the following directory:

.. code:: c

    c/src/lib/libcpu/*CPU*

CPU model dependent support code is found in the following directory:

.. code:: c

    c/src/lib/libcpu/*CPU*/*CPU_MODEL*

*CPU_MODEL* may be a specific CPU model name or a name indicating a CPU
core or a set of related CPU models.  The file ``configure.ac`` in each ``c/src/lib/libcpu/*CPU*`` directory contains the logic which enables
the appropriate subdirectories for the specific CPU model your BSP has.

Board Support Package Structure
===============================

The BSPs are all under the ``c/src/lib/libbsp`` directory.  Below this
directory, there is a subdirectory for each CPU family.  Each BSP
is found under the subdirectory for the appropriate processor
family (m68k, powerpc, etc.).  In addition, there is source code
available which may be shared across all BSPs regardless of
the CPU family or just across BSPs within a single CPU family.  This
results in a BSP using the following directories:
.. code:: c

    c/src/lib/libbsp/shared
    c/src/lib/libbsp/*CPU*/shared
    c/src/lib/libbsp/*CPU*/*BSP*

Under each BSP specific directory, there is a collection of
subdirectories.  For commonly provided functionality, the BSPs
follow a convention on subdirectory naming.  The following list
describes the commonly found subdirectories under each BSP.

- *console*:
  is technically the serial driver for the BSP rather
  than just a console driver, it deals with the board
  UARTs (i.e. serial devices).

- *clock*:
  support for the clock tick – a regular time basis to the kernel.

- *timer*:
  support of timer devices.

- *rtc* or ``tod``:
  support for the hardware real-time clock.

- *nvmem*:
  support for non-volatile memory such as EEPROM or Flash.

- *network*:
  the Ethernet driver.

- *shmsupp*:
  support of shared memory driver MPCI layer in a multiprocessor system,

- *include*:
  include files for this BSP.

- *gnatsupp*:
  BSP specific support for the GNU Ada run-time.  Each BSP that wishes
  to have the possibility to map faults or exceptions into Ada language
  exceptions or hardware interrupts into Ada interrupt tasks must provide
  this support.

There may be other directories in the BSP tree and the name should
be indicative of the functionality of the code within that directory.

The build order of the BSP is determined by the Makefile structure.
This structure is discussed in more detail in the `Makefiles`_
chapter.

*NOTE:* This manual refers to the gen68340 BSP for numerous concrete
examples.  You should have a copy of the gen68340 BSP available while
reading this piece of documentation.   This BSP is located in the
following directory:
.. code:: c

    c/src/lib/libbsp/m68k/gen68340

Later in this document, the $BSP340_ROOT label will be used
to refer to this directory.

.. COMMENT: COPYRIGHT (c) 1988-2008.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.


Makefiles
#########

This chapter discusses the Makefiles associated with a BSP.  It does not
describe the process of configuring, building, and installing RTEMS.
This chapter will not provide detailed information about this process.
Nonetheless, it is important to remember that the general process consists
of four phases as shown here:

- .. code:: c

      bootstrap

- .. code:: c

      configure

- .. code:: c

      build

- .. code:: c

      install

During the bootstrap phase, you are using the ``configure.ac`` and``Makefile.am`` files as input to GNU autoconf and automake to
generate a variety of files.  This is done by running the ``bootstrap``
script found at the top of the RTEMS source tree.

During the configure phase, a number of files are generated.  These
generated files are tailored for the specific host/target combination
by the configure script.  This set of files includes the Makefiles used
to actually compile and install RTEMS.

During the build phase, the source files are compiled into object files
and libraries are built.

During the install phase, the libraries, header files, and other support
files are copied to the BSP specific installation point.  After installation
is successfully completed, the files generated by the configure and build
phases may be removed.

Makefiles Used During The BSP Building Process
==============================================

RTEMS uses the *GNU automake* and *GNU autoconf* automatic
configuration package.  Consequently, there are a number of
automatically generated files in each directory in the RTEMS
source tree.  The ``bootstrap`` script found in the top level
directory of the RTEMS source tree is executed to produce the
automatically generated files.  That script must be run from
a directory with a ``configure.ac`` file in it.  The ``bootstrap``
command is usually invoked in one of the following manners:

- ``bootstrap`` to regenerate all files that are generated by
  autoconf and automake.

- ``bootstrap -c`` to remove all files generated by autoconf and
  automake.

- ``bootstrap -p`` to regenerate ``preinstall.am`` files.

There is a file named ``Makefile.am`` in each directory of
a BSP.  This file is used by *automake* to produce the file named``Makefile.in`` which is also found in each directory of a BSP.
When modifying a ``Makefile.am``, you can probably find examples of
anything you need to do in one of the BSPs.

The configure process specializes the ``Makefile.in`` files at the time that RTEMS
is configured for a specific development host and target.  Makefiles
are automatically generated from the ``Makefile.in`` files.  It is
necessary for the BSP developer to provide the ``Makefile.am``
files and generate the ``Makefile.in`` files.  Most of the
time, it is possible to copy the ``Makefile.am`` from another
similar directory and edit it.

The ``Makefile`` files generated are processed when configuring
and building RTEMS for a given BSP.

The BSP developer is responsible for generating ``Makefile.am``
files which properly build all the files associated with their BSP.
Most BSPs will only have a single ``Makefile.am`` which details
the set of source files to build to compose the BSP support library
along with the set of include files that are to be installed.

This single ``Makefile.am`` at the top of the BSP tree specifies
the set of header files to install.  This fragment from the SPARC/ERC32
BSP results in four header files being installed.
.. code:: c

    include_HEADERS = include/bsp.h
    include_HEADERS += include/tm27.h
    include_HEADERS += include/erc32.h
    include_HEADERS += include/coverhd.h

When adding new include files, you will be adding to the set of``include_HEADERS``.  When you finish editing the ``Makefile.am``
file, do not forget to run ``bootstrap -p`` to regenerate the``preinstall.am``.

The ``Makefile.am`` also specifies which source files to build.
By convention, logical components within the BSP each assign their
source files to a unique variable.  These variables which define
the source files are collected into a single variable which instructs
the GNU autotools that we are building ``libbsp.a``.  This fragment
from the SPARC/ERC32 BSP shows how the startup related, miscellaneous
support code, and the console device driver source is managed
in the ``Makefile.am``.
.. code:: c

    startup_SOURCES = ../../sparc/shared/bspclean.c ../../shared/bsplibc.c \\
    ../../shared/bsppredriverhook.c \\
    ../../shared/bsppost.c ../../sparc/shared/bspstart.c \\
    ../../shared/bootcard.c ../../shared/sbrk.c startup/setvec.c \\
    startup/spurious.c startup/erc32mec.c startup/boardinit.S
    clock_SOURCES = clock/ckinit.c
    ...
    noinst_LIBRARIES = libbsp.a
    libbsp_a_SOURCES = $(startup_SOURCES) $(console_SOURCES) ...

When adding new files to an existing directory, do not forget to add
the new files to the list of files to be built in the corresponding``XXX_SOURCES`` variable in the ``Makefile.am`` and run``bootstrap``.

Some BSPs use code that is built in ``libcpu``.  If you BSP does
this, then you will need to make sure the objects are pulled into your
BSP library.  The following from the SPARC/ERC32 BSP pulls in the cache,
register window management and system call support code from the directory
corresponding to its ``RTEMS_CPU`` model.
.. code:: c

    libbsp_a_LIBADD  = ../../../libcpu/@RTEMS_CPU@/cache.rel \\
    ../../../libcpu/@RTEMS_CPU@/reg_win.rel \\
    ../../../libcpu/@RTEMS_CPU@/syscall.rel

*NOTE:* The ``Makefile.am`` files are ONLY processed by``bootstrap`` and the resulting ``Makefile.in`` files are only
processed during the configure process of a RTEMS build. Therefore,
when developing a BSP and adding a new file to a ``Makefile.am``,
the already generated ``Makefile`` will not automatically
include the new references unless you configured RTEMS with the``--enable-maintainer-mode`` option.  Otherwise, the new file not
being be taken into account!

Creating a New BSP Make Customization File
==========================================

When building a BSP or an application using that BSP, it is necessary
to tailor the compilation arguments to account for compiler flags, use
custom linker scripts, include the RTEMS libraries, etc..  The BSP
must be built using this information.  Later, once the BSP is installed
with the toolset, this same information must be used when building the
application.  So a BSP must include a build configuration file.  The
configuration file is ``make/custom/BSP.cfg``.

The configuration file is taken into account when building one’s
application using the RTEMS template Makefiles (``make/templates``).
These application template Makefiles have been included with the
RTEMS source distribution since the early 1990’s.  However there is
a desire in the RTEMS user community to move all provided examples to
GNU autoconf. They are included in the 4.9 release series and used for
all examples provided with RTEMS. There is no definite time table for
obsoleting them.  You are free to use these but be warned they have
fallen out of favor with many in the RTEMS community and may disappear
in the future.

The following is a slightly shortened version of the make customization
file for the gen68340 BSP.  The original source for this file can be
found in the ``make/custom`` directory.
.. code:: c

    # The RTEMS CPU Family and Model
    RTEMS_CPU=m68k
    RTEMS_CPU_MODEL=m68340
    include $(RTEMS_ROOT)/make/custom/default.cfg
    # This is the actual bsp directory used during the build process.
    RTEMS_BSP_FAMILY=gen68340
    # This contains the compiler options necessary to select the CPU model
    # and (hopefully) optimize for it.
    CPU_CFLAGS = -mcpu=cpu32
    # optimize flag: typically -O2
    CFLAGS_OPTIMIZE_V = -O2 -g -fomit-frame-pointer

The make customization files have generally grown simpler and simpler
with each RTEMS release.  Beginning in the 4.9 release series, the rules
for linking an RTEMS application are shared by all BSPs.  Only BSPs which
need to perform a transformation from linked ELF file to a downloadable
format have any additional actions for program link time. In 4.8 and
older, every BSP specified the "make executable" or ``make-exe``
rule and duplicated the same actions.

It is generally easier to copy a ``make/custom`` file from a
BSP similar to the one being developed.

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Linker Script
#############

What is a "linkcmds" file?
==========================

The ``linkcmds`` file is a script which is passed to the linker at linking
time.  This file describes the memory configuration of the board as needed
to link the program.  Specifically it specifies where the code and data
for the application will reside in memory.

The format of the linker script is defined by the GNU Loader ``ld``
which is included as a component of the GNU Binary Utilities.  If you
are using GNU/Linux, then you probably have the documentation installed
already and are using these same tools configured for *native* use.
Please visit the Binutils project http://sourceware.org/binutils/
if you need more information.

Program Sections
================

An embedded systems programmer must be much more aware of the
placement of their executable image in memory than the average
applications programmer.  A program destined to be embedded as well
as the target system have some specific properties that must be
taken into account. Embedded machines often mean average performances
and small memory usage.  It is the memory usage that concerns us
when examining the linker command file.

Two types of memories have to be distinguished:

- RAM - volatile offering read and write access

- ROM - non-volatile but read only

Even though RAM and ROM can be found in every personal computer,
one generally doesn’t care about them.  In a personal computer,
a program is nearly always stored on disk and executed in RAM.  Things
are a bit different for embedded targets: the target will execute the
program each time it is rebooted or switched on.   The application
program is stored in non-volatile memory such as ROM, PROM, EEPROM,
or Flash. On the other hand, data processing occurs in RAM.

This leads us to the structure of an embedded program.  In rough terms,
an embedded program is made of sections.  It is the responsibility of
the application programmer to place these sections in the appropriate
place in target memory.  To make this clearer, if using the COFF
object file format on the Motorola m68k family of microprocessors,
the following sections will be present:

- *code (``.text``) section*:
  is the program’s code and it should not be modified.
  This section may be placed in ROM.

- *non-initialized data (``.bss``) section*:
  holds uninitialized variables of the program. It can stay in RAM.

- *initialized data (``.data``) section*:
  holds the initialized program data which may be modified during the
  program’s life.  This means they have to be in RAM.
  On the other hand, these variables must be set to predefined values, and
  those predefined values have to be stored in ROM.

*NOTE:* Many programs and support libraries unknowingly assume that the``.bss`` section and, possibly, the application heap are initialized
to zero at program start.  This is not required by the ISO/ANSI C Standard
but is such a common requirement that most BSPs do this.

That brings us up to the notion of the image of an executable: it consists
of the set of the sections that together constitute the application.

Image of an Executable
======================

As a program executable has many sections (note that the user can define
their own, and that compilers define theirs without any notice), one has to
specify the placement of each section as well as the type of memory
(RAM or ROM) the sections will be placed into.
For instance, a program compiled for a Personal Computer will see all the
sections to go to RAM, while a program destined to be embedded will see
some of his sections going into the ROM.

The connection between a section and where that section is loaded into
memory is made at link time.  One has to let the linker know where
the different sections are to be placed once they are in memory.

The following example shows a simple layout of program sections.  With
some object formats, there are many more sections but the basic
layout is conceptually similar.
.. code:: c

    +-----------------+-------------+
    |     .text       |  RAM or ROM |
    +-----------------+-------------+
    |     .data       |  RAM        |
    +-----------------+-------------+
    |     .bss        |  RAM        |
    +-----------------+-------------+

Example Linker Command Script
=============================

The GNU linker has a command language to specify the image format.  This
command language can be quite complicated but most of what is required
can be learned by careful examination of a well-documented example.
The following is a heavily commented version of the linker script
used with the the ``gen68340`` BSP  This file can be found at
$BSP340_ROOT/startup/linkcmds.
.. code:: c

    /*
    *  Specify that the output is to be coff-m68k regardless of what the
    *  native object format is.
    \*/
    OUTPUT_FORMAT(coff-m68k)
    /*
    *  Set the amount of RAM on the target board.
    *
    *  NOTE: The default may be overridden by passing an argument to ld.
    \*/
    RamSize = DEFINED(RamSize) ? RamSize : 4M;
    /*
    *  Set the amount of RAM to be used for the application heap.  Objects
    *  allocated using malloc() come from this area.  Having a tight heap
    *  size is somewhat difficult and multiple attempts to squeeze it may
    *  be needed reducing memory usage is important.  If all objects are
    *  allocated from the heap at system initialization time, this eases
    *  the sizing of the application heap.
    *
    *  NOTE 1: The default may be overridden by passing an argument to ld.
    *
    *  NOTE 2: The TCP/IP stack requires additional memory in the Heap.
    *
    *  NOTE 3: The GNAT/RTEMS run-time requires additional memory in
    *  the Heap.
    \*/
    HeapSize = DEFINED(HeapSize) ? HeapSize : 0x10000;
    /*
    *  Set the size of the starting stack used during BSP initialization
    *  until first task switch.  After that point, task stacks allocated
    *  by RTEMS are used.
    *
    *  NOTE: The default may be overridden by passing an argument to ld.
    \*/
    StackSize = DEFINED(StackSize) ? StackSize : 0x1000;
    /*
    *  Starting addresses and length of RAM and ROM.
    *
    *  The addresses must be valid addresses on the board.  The
    *  Chip Selects should be initialized such that the code addresses
    *  are valid.
    \*/
    MEMORY {
    ram : ORIGIN = 0x10000000, LENGTH = 4M
    rom : ORIGIN = 0x01000000, LENGTH = 4M
    }
    /*
    *  This is for the network driver.  See the Networking documentation
    *  for more details.
    \*/
    ETHERNET_ADDRESS =
    DEFINED(ETHERNET_ADDRESS) ? ETHERNET_ADDRESS : 0xDEAD12;
    /*
    *  The following defines the order in which the sections should go.
    *  It also defines a number of variables which can be used by the
    *  application program.
    *
    *  NOTE: Each variable appears with 1 or 2 leading underscores to
    *        ensure that the variable is accessible from C code with a
    *        single underscore.  Some object formats automatically add
    *        a leading underscore to all C global symbols.
    \*/
    SECTIONS {
    /*
    *  Make the RomBase variable available to the application.
    \*/
    _RamSize = RamSize;
    __RamSize = RamSize;
    /*
    *  Boot PROM  - Set the RomBase variable to the start of the ROM.
    \*/
    rom : {
    _RomBase = .;
    __RomBase = .;
    } >rom
    /*
    * Dynamic RAM - set the RamBase variable to the start of the RAM.
    \*/
    ram : {
    _RamBase = .;
    __RamBase = .;
    } >ram
    /*
    *  Text (code) goes into ROM
    \*/
    .text : {
    /*
    *  Create a symbol for each object (.o).
    \*/
    CREATE_OBJECT_SYMBOLS
    /*
    *  Put all the object files code sections here.
    \*/
    \*(.text)
    . = ALIGN (16);      /*  go to a 16-byte boundary \*/
    /*
    *  C++ constructors and destructors
    *
    *  NOTE:  See the CROSSGCC mailing-list FAQ for
    *         more details about the "\[......]".
    \*/
    __CTOR_LIST__ = .;
    \[......]
    __DTOR_END__ = .;
    /*
    *  Declares where the .text section ends.
    \*/
    etext = .;
    _etext = .;
    } >rom
    /*
    *  Exception Handler Frame section
    \*/
    .eh_fram : {
    . = ALIGN (16);
    \*(.eh_fram)
    } >ram
    /*
    *  GCC Exception section
    \*/
    .gcc_exc : {
    . = ALIGN (16);
    \*(.gcc_exc)
    } >ram
    /*
    *  Special variable to let application get to the dual-ported
    *  memory.
    \*/
    dpram : {
    m340 = .;
    _m340 = .;
    . += (8 * 1024);
    } >ram
    /*
    *  Initialized Data section goes in RAM
    \*/
    .data : {
    copy_start = .;
    \*(.data)
    . = ALIGN (16);
    _edata = .;
    copy_end = .;
    } >ram
    /*
    *  Uninitialized Data section goes in ROM
    \*/
    .bss : {
    /*
    *  M68K specific: Reserve some room for the Vector Table
    *  (256 vectors of 4 bytes).
    \*/
    M68Kvec = .;
    _M68Kvec = .;
    . += (256 * 4);
    /*
    *  Start of memory to zero out at initialization time.
    \*/
    clear_start = .;
    /*
    *  Put all the object files uninitialized data sections
    *  here.
    \*/
    \*(.bss)
    \*(COMMON)
    . = ALIGN (16);
    _end = .;
    /*
    *  Start of the Application Heap
    \*/
    _HeapStart = .;
    __HeapStart = .;
    . += HeapSize;
    /*
    *  The Starting Stack goes after the Application Heap.
    *  M68K stack grows down so start at high address.
    \*/
    . += StackSize;
    . = ALIGN (16);
    stack_init = .;
    clear_end = .;
    /*
    *  The RTEMS Executive Workspace goes here.  RTEMS
    *  allocates tasks, stacks, semaphores, etc. from this
    *  memory.
    \*/
    _WorkspaceBase = .;
    __WorkspaceBase = .;
    } >ram
    }

Initialized Data
================

Now there’s a problem with the initialized data: the ``.data`` section
has to be in RAM as this data may be modified during the program execution.
But how will the values be initialized at boot time?

One approach is to place the entire program image in RAM and reload
the image in its entirety each time the program is run.  This is fine
for use in a debug environment where a high-speed connection is available
between the development host computer and the target.  But even in this
environment, it is cumbersome.

The solution is to place a copy of the initialized data in a separate
area of memory and copy it into the proper location each time the
program is started.  It is common practice to place a copy of the initialized ``.data`` section at the end of the code (``.text``) section
in ROM when building a PROM image. The GNU tool ``objcopy``
can be used for this purpose.

The following figure illustrates the steps a linked program goes through
to become a downloadable image.


+--------------+-----+--------------------+--------------------------+
| .data    RAM |     | .data          RAM |                          |
+--------------+     +--------------------+                          |
| .bss     RAM |     | .bss           RAM |                          | 
+--------------+     +--------------------+-----+--------------------+
| .text    ROM |     | .text          ROM |     |     .text          |
+--------------+-----+---------+----------+-----+--------------------+
| copy of .data  ROM |         | copy of .data  |                    |
+--------------------+---------+----------------+--------------------+
|  Step 1            |Step 2                       Step 3            |
+--------------------+--------------------------+--------------------+

In Step 1, the program is linked together using the BSP linker script.

In Step 2, a copy is made of the ``.data`` section and placed
after the ``.text`` section so it can be placed in PROM.  This step
is done after the linking time.  There is an example
of doing this in the file $RTEMS_ROOT/make/custom/gen68340.cfg:
.. code:: c

    # make a PROM image using objcopy
    m68k-rtems-objcopy \\
    --adjust-section-vma .data= \\
    \`m68k-rtems-objdump --section-headers \\
    $(basename $@).exe \\
    | awk '\[...]` \\
    $(basename $@).exe

NOTE: The address of the "copy of ``.data`` section" is
created by extracting the last address in the ``.text``
section with an ``awk`` script.  The details of how
this is done are not relevant.

Step 3 shows the final executable image as it logically appears in
the target’s non-volatile program memory.  The board initialization
code will copy the ""copy of ``.data`` section" (which are stored in
ROM) to their reserved location in RAM.

.. COMMENT: COPYRIGHT (c) 1988-2011.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Miscellaneous Support Files
###########################

GCC Compiler Specifications File
================================

The file ``bsp_specs`` defines the start files and libraries
that are always used with this BSP.  The format of this file
is admittedly cryptic and this document will make no attempt
to explain it completely.  Below is the ``bsp_specs``
file from the PowerPC psim BSP:
.. code:: c

    %rename endfile old_endfile
    %rename startfile old_startfile
    %rename link old_link
    \*startfile:
    %{!qrtems: %(old_startfile)} \\
    %{!nostdlib: %{qrtems: ecrti%O%s rtems_crti%O%s crtbegin.o%s start.o%s}}
    \*link:
    %{!qrtems: %(old_link)} %{qrtems: -Qy -dp -Bstatic -e _start -u __vectors}
    \*endfile:
    %{!qrtems: %(old_endfile)} %{qrtems: crtend.o%s ecrtn.o%s}

The first section of this file renames the built-in definition of
some specification variables so they can be augmented without
embedded their original definition.  The subsequent sections
specify what behavior is expected when the ``-qrtems`` option is specified.

The ``*startfile`` section specifies that the BSP specific file``start.o`` will be used instead of ``crt0.o``.  In addition,
various EABI support files (``ecrti.o`` etc.) will be linked in with
the executable.

The ``*link`` section adds some arguments to the linker when it is
invoked by GCC to link an application for this BSP.

The format of this file is specific to the GNU Compiler Suite.  The
argument used to override and extend the compiler built-in specifications
is available in all recent GCC versions.  The ``-specs`` option is
present in all ``egcs`` distributions and ``gcc`` distributions
starting with version 2.8.0.

README Files
============

Most BSPs provide one or more ``README`` files.  Generally, there
is a ``README`` file at the top of the BSP source.  This file
describes the board and its hardware configuration, provides vendor
information, local configuration information, information on downloading
code to the board, debugging, etc..  The intent of this
file is to help someone begin to use the BSP faster.

A ``README`` file in a BSP subdirectory typically explains something
about the contents of that subdirectory in greater detail.  For example,
it may list the documentation available for a particular peripheral
controller and how to obtain that documentation.  It may also explain some
particularly cryptic part of the software in that directory or provide
rationale on the implementation.

times
=====

This file contains the results of the RTEMS Timing Test Suite.  It is
in a standard format so that results from one BSP can be easily compared
with those of another target board.

If a BSP supports multiple variants, then there may be multiple ``times``
files.  Usually these are named ``times.VARIANTn``.

Tools Subdirectory
==================

Some BSPs provide additional tools that aid in using the target board.
These tools run on the development host and are built as part of building
the BSP.  Most common is a script to automate running the RTEMS Test Suites
on the BSP.  Examples of this include:

- ``powerpc/psim`` includes scripts to ease use of the simulator

- ``m68k/mvme162`` includes a utility to download across the
  VMEbus into target memory if the host is a VMEbus board in the same
  chasis.

bsp.h Include File
==================

The file ``include/bsp.h`` contains prototypes and definitions
specific to this board.  Every BSP is required to provide a ``bsp.h``.
The best approach to writing a ``bsp.h`` is copying an existing one
as a starting point.

Many ``bsp.h`` files provide prototypes of variables defined
in the linker script (``linkcmds``).

tm27.h Include File
===================

The ``tm27`` test from the RTEMS Timing Test Suite is designed to measure the length of time required to vector to and return from an interrupt handler. This test requires some help from the BSP to know how to cause and manipulate the interrupt source used for this measurement.  The following is a list of these:

- ``MUST_WAIT_FOR_INTERRUPT`` - modifies behavior of ``tm27``.

- ``Install_tm27_vector`` - installs the interrupt service
  routine for the Interrupt Benchmark Test (``tm27``).

- ``Cause_tm27_intr`` - generates the interrupt source
  used in the Interrupt Benchmark Test (``tm27``).

- ``Clear_tm27_intr`` - clears the interrupt source
  used in the Interrupt Benchmark Test (``tm27``).

- ``Lower_tm27_intr`` - lowers the interrupt mask so the
  interrupt source used in the Interrupt Benchmark Test (``tm27``)
  can generate a nested interrupt.

All members of the Timing Test Suite are designed to run *WITHOUT*
the Clock Device Driver installed.  This increases the predictability
of the tests’ execution as well as avoids occassionally including the
overhead of a clock tick interrupt in the time reported.  Because of
this it is sometimes possible to use the clock tick interrupt source
as the source of this test interrupt.  On other architectures, it is
possible to directly force an interrupt to occur.

Calling Overhead File
=====================

The file ``include/coverhd.h`` contains the overhead associated
with invoking each directive.  This overhead consists of the execution
time required to package the parameters as well as to execute the "jump to
subroutine" and "return from subroutine" sequence.  The intent of this
file is to help separate the calling overhead from the actual execution
time of a directive.  This file is only used by the tests in the
RTEMS Timing Test Suite.

The numbers in this file are obtained by running the "Timer Overhead"``tmoverhd`` test.  The numbers in this file may be 0 and no
overhead is subtracted from the directive execution times reported by
the Timing Suite.

There is a shared implementation of ``coverhd.h`` which sets all of
the overhead constants to 0.  On faster processors, this is usually the
best alternative for the BSP as the calling overhead is extremely small.
This file is located at:
.. code:: c

    c/src/lib/libbsp/shared/include/coverhd.h

sbrk() Implementation
=====================

Although nearly all BSPs give all possible memory to the C Program Heap
at initialization, it is possible for a BSP to configure the initial
size of the heap small and let it grow on demand.  If the BSP wants
to dynamically extend the heap used by the C Library memory allocation
routines (i.e. ``malloc`` family), then the``sbrk`` routine must
be functional.  The following is the prototype for this routine:
.. code:: c

    void * sbrk(size_t increment)

The ``increment`` amount is based upon the ``sbrk_amount``
parameter passed to the ``bsp_libc_init`` during system initialization... index:: CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK

If your BSP does not want to support dynamic heap extension, then you do not have to do anything special.  However, if you want to support ``sbrk``, you must provide an implementation of this method and define ``CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK`` in ``bsp.h``.  This informs ``rtems/confdefs.h`` to configure the Malloc Family Extensions which support ``sbrk``.

bsp_fatal_extension() - Cleanup the Hardware
============================================

The ``bsp_fatal_extension()`` is an optional BSP specific initial extension
invoked once a fatal system state is reached.  Most of the BSPs use the same
shared version of ``bsp_fatal_extension()`` that does nothing or performs a
system reset.  This implementation is located in the following file:
.. code:: c

    c/src/lib/libbsp/shared/bspclean.c

The ``bsp_fatal_extension()`` routine can be used to return to a ROM
monitor, insure that interrupt sources are disabled, etc..  This routine is the
last place to ensure a clean shutdown of the hardware.  The fatal source,
internal error indicator, and the fatal code arguments are available to
evaluate the fatal condition.  All of the non-fatal shutdown sequences
ultimately pass their exit status to ``rtems_shutdown_executive`` and this
is what is passed to this routine in case the fatal source is
RTEMS_FATAL_SOURCE_EXIT.

On some BSPs, it prints a message indicating that the application
completed execution and waits for the user to press a key before
resetting the board.  The PowerPC/gen83xx and PowerPC/gen5200 BSPs do
this when they are built to support the FreeScale evaluation boards.
This is convenient when using the boards in a development environment
and may be disabled for production use.

Configuration Macros
====================

Each BSP can define macros in bsp.h which alter some of the the default configuration parameters in ``rtems/confdefs.h``.  This section describes those macros:

- .. index:: CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK

  ``CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK`` must be defined if the
  BSP has proper support for ``sbrk``.  This is discussed in more detail
  in the previous section.

- .. index:: BSP_IDLE_TASK_BODY

  ``BSP_IDLE_TASK_BODY`` may be defined to the entry point of a
  BSP specific IDLE thread implementation.  This may be overridden if the
  application provides its own IDLE task implementation.

- .. index:: BSP_IDLE_TASK_STACK_SIZE

  ``BSP_IDLE_TASK_STACK_SIZE`` may be defined to the desired
  default stack size for the IDLE task as recommended when using this BSP.

- .. index:: BSP_INTERRUPT_STACK_SIZE

  ``BSP_INTERRUPT_STACK_SIZE`` may be defined to the desired default interrupt stack size as recommended when using this BSP.  This is sometimes required when the BSP developer has knowledge of stack intensive interrupt handlers.

- .. index:: BSP_ZERO_WORKSPACE_AUTOMATICALLY

  ``BSP_ZERO_WORKSPACE_AUTOMATICALLY`` is defined when the BSP
  requires that RTEMS zero out the RTEMS C Program Heap at initialization.
  If the memory is already zeroed out by a test sequence or boot ROM,
  then the boot time can be reduced by not zeroing memory twice.

- .. index:: BSP_DEFAULT_UNIFIED_WORK_AREAS

  ``BSP_DEFAULT_UNIFIED_WORK_AREAS`` is defined when the BSP
  recommends that the unified work areas configuration should always
  be used.  This is desirable when the BSP is known to always have very
  little RAM and thus saving memory by any means is desirable.

set_vector() - Install an Interrupt Vector
==========================================

On targets with Simple Vectored Interrupts, the BSP must provide
an implementation of the ``set_vector`` routine.  This routine is
responsible for installing an interrupt vector.  It invokes the support
routines necessary to install an interrupt handler as either a "raw"
or an RTEMS interrupt handler.  Raw handlers bypass the RTEMS interrupt
structure and are responsible for saving and restoring all their own
registers.  Raw handlers are useful for handling traps, debug vectors,
etc..

The ``set_vector`` routine is a central place to perform interrupt
controller manipulation and encapsulate that information.  It is usually
implemented as follows:

.. code:: c

    rtems_isr_entry set_vector(                     /* returns old vector \*/
    rtems_isr_entry     handler,                  /* isr routine        \*/
    rtems_vector_number vector,                   /* vector number      \*/
    int                 type                      /* RTEMS or RAW intr  \*/
    )
    {
    if the type is RAW
    install the raw vector
    else
    use rtems_interrupt_catch to install the vector
    perform any interrupt controller necessary to unmask
    the interrupt source
    return the previous handler
    }

*NOTE:* The i386, PowerPC and ARM ports use a Programmable
Interrupt Controller model which does not require the BSP to implement``set_vector``.  BSPs for these architectures must provide a different
set of support routines.

Interrupt Delay Profiling
=========================

The RTEMS profiling needs support by the BSP for the interrupt delay 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) a BSP may provide data for the interrupt
delay times.  The BSP can feed interrupt delay times with the``_Profiling_Update_max_interrupt_delay()`` function
(``#include <rtems/score/profiling.h>``).  For an example please have a look
at ``c/src/lib/libbsp/sparc/leon3/clock/ckinit.c``.

Programmable Interrupt Controller API
=====================================

A BSP can use the PIC API to install Interrupt Service Routines through
a set of generic methods. In order to do so, the header files
libbsp/shared/include/irq-generic.h and libbsp/shared/include/irq-info.h
must be included by the bsp specific irq.h file present in the include/
directory. The irq.h acts as a BSP interrupt support configuration file which
is used to define some important MACROS. It contains the declarations for
any required global functions like bsp_interrupt_dispatch(). Thus later on,
every call to the PIC interface requires including <bsp/irq.h>

The generic interrupt handler table is intitalized by invoking the``bsp_interrupt_initialize()`` method from bsp_start() in the bspstart.c
file which sets up this table to store the ISR addresses, whose size is based
on the definition of macros, BSP_INTERRUPT_VECTOR_MIN & BSP_INTERRUPT_VECTOR_MAX
in include/bsp.h

For the generic handler table to properly function, some bsp specific code is
required, that should be present in irq/irq.c . The bsp-specific functions required
to be writen by the BSP developer are :

- .. index:: bsp_interrupt_facility_initialize()

  ``bsp_interrupt_facility_initialize()`` contains bsp specific interrupt
  initialization code(Clear Pending interrupts by modifying registers, etc.).
  This method is called from bsp_interrupt_initialize() internally while setting up
  the table.

- .. index:: bsp_interrupt_handler_default()

  ``bsp_interrupt_handler_default()`` acts as a fallback handler when
  no ISR address has been provided corresponding to a vector in the table.

- .. index:: bsp_interrupt_dispatch()

  ``bsp_interrupt_dispatch()`` service the ISR by handling
  any bsp specific code & calling the generic method bsp_interrupt_handler_dispatch()
  which in turn services the interrupt by running the ISR after looking it up in
  the table. It acts as an entry to the interrupt switchboard, since the bsp
  branches to this function at the time of occurrence of an interrupt.

- .. index:: bsp_interrupt_vector_enable()

  ``bsp_interrupt_vector_enable()`` enables interrupts and is called in
  irq-generic.c while setting up the table.

- .. index:: bsp_interrupt_vector_disable()

  ``bsp_interrupt_vector_disable()`` disables interrupts and is called in
  irq-generic.c while setting up the table & during other important parts.

An interrupt handler is installed or removed with the help of the following functions :

.. code:: c

    rtems_status_code rtems_interrupt_handler_install(   /* returns status code \*/
    rtems_vector_number vector,                        /* interrupt vector \*/
    const char \*info,                           /* custom identification text \*/
    rtems_option options,                              /* Type of Interrupt \*/
    rtems_interrupt_handler handler,                   /* interrupt handler \*/
    void \*arg  /* parameter to be passed to handler at the time of invocation \*/
    )
    rtems_status_code rtems_interrupt_handler_remove(   /* returns status code \*/
    rtems_vector_number vector,                       /* interrupt vector \*/
    rtems_interrupt_handler handler,                  /* interrupt handler \*/
    void \*arg                          /* parameter to be passed to handler \*/
    )

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Ada95 Interrupt Support
#######################

Introduction
============

This chapter describes what is required to enable Ada interrupt
and error exception handling when using GNAT over RTEMS.

The GNAT Ada95 interrupt support RTEMS was developed by
Jiri Gaisler <jgais@ws.estec.esa.nl> who also wrote this
chapter.

Mapping Interrupts to POSIX Signals
===================================

In Ada95, interrupts can be attached with the interrupt_attach pragma.
For most systems, the gnat run-time will use POSIX signal to implement
the interrupt handling, mapping one signal per interrupt. For interrupts
to be propagated to the attached Ada handler, the corresponding signal
must be raised when the interrupt occurs.

The same mechanism is used to generate Ada error exceptions.
Three error exceptions are defined: program, constraint and storage
error. These are generated by raising the predefined signals: SIGILL,
SIGFPE and SIGSEGV. These signals should be raised when a spurious
or erroneous trap occurs.

To enable gnat interrupt and error exception support for a particular
BSP, the following has to be done:

# Write an interrupt/trap handler that will raise the corresponding
  signal depending on the interrupt/trap number.

# Install the interrupt handler for all interrupts/traps that will be
  handled by gnat (including spurious).

# At startup, gnat calls ``__gnat_install_handler()``. The BSP
  must provide this function which installs the interrupt/trap handlers.

Which CPU-interrupt will generate which signal is implementation
defined. There are 32 POSIX signals (1 - 32), and all except the
three error signals (SIGILL, SIGFPE and SIGSEGV) can be used. I
would suggest to use the upper 16 (17 - 32) which do not
have an assigned POSIX name.

Note that the pragma interrupt_attach will only bind a signal
to a particular Ada handler - it will not unmask the
interrupt or do any other things to enable it. This have to be
done separately, typically by writing various device register.

Example Ada95 Interrupt Program
===============================

An example program (``irq_test``) is included in the
Ada examples package to show how interrupts can be handled
in Ada95. Note that generation of the test interrupt
(``irqforce.c``) is BSP specific and must be edited.

NOTE: The ``irq_test`` example was written for the SPARC/ERC32
BSP.

Version Requirements
====================

With RTEMS 4.0, a patch was required to psignal.c in RTEMS
sources (to correct a bug associated to the default action of
signals 15-32).   The SPARC/ERC32 RTEMS BSP includes the``gnatsupp`` subdirectory that can be used as an example
for other BSPs.

With GNAT 3.11p, a patch is required for ``a-init.c`` to invoke
the BSP specific routine that installs the exception handlers.

.. COMMENT: COPYRIGHT (c) 1988-2008.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Initialization Code
###################

Introduction
============

The initialization code is the first piece of code executed when there’s a
reset/reboot. Its purpose is to initialize the board for the application.
This chapter contains a narrative description of the initialization
process followed by a description of each of the files and routines
commonly found in the BSP related to initialization.  The remainder of
this chapter covers special issues which require attention such
as interrupt vector table and chip select initialization.

Most of the examples in this chapter will be based on the SPARC/ERC32 and
m68k/gen68340 BSP initialization code.  Like most BSPs, the initialization
for these BSP is divided into two subdirectories under the BSP source
directory.  The BSP source code for these BSPs is in the following
directories:
.. code:: c

    c/src/lib/libbsp/m68k/gen68340
    c/src/lib/libbsp/sparc/erc32

Both BSPs contain startup code written in assembly language and C.
The gen68340 BSP has its early initialization start code in the``start340`` subdirectory and its C startup code in the ``startup``
directory.  In the ``start340`` directory are two source files.
The file ``startfor340only.s`` is the simpler of these files as it only
has initialization code for a MC68340 board.  The file ``start340.s``
contains initialization for a 68349 based board as well.

Similarly, the ERC32 BSP has startup code written in assembly language
and C.  However, this BSP shares this code with other SPARC BSPs.
Thus the ``Makefile.am`` explicitly references the following files
for this functionality.
.. code:: c

    ../../sparc/shared/start.S

*NOTE:* In most BSPs, the directory named ``start340`` in the
gen68340 BSP would be simply named ``start`` or start followed by a
BSP designation.

Required Global Variables
=========================

Although not strictly part of initialization, there are a few global
variables assumed to exist by reusable device drivers.  These global
variables should only defined by the BSP when using one of these device
drivers.

The BSP author probably should be aware of the ``Configuration``
Table structure generated by ``<rtems/confdefs.h>`` during debug but
should not explicitly reference it in the source code.  There are helper
routines provided by RTEMS to access individual fields.

In older RTEMS versions, the BSP included a number of required global
variables.  We have made every attempt to eliminate these in the interest
of simplicity.

Board Initialization
====================

This section describes the steps an application goes through from the
time the first BSP code is executed until the first application task
executes.  The following figure illustrates the program flow during
this sequence:

IMAGE NOT AVAILABLE IN ASCII VERSION

The above figure illustrates the flow from assembly language start code
to the shared ``bootcard.c`` framework then through the C Library,
RTEMS, device driver initialization phases, and the context switch
to the first application task.  After this, the application executes
until it calls ``exit``, ``rtems_shutdown_executive``, or some
other normal termination initiating routine and a fatal system state is
reached.  The optional ``bsp_fatal_extension`` initial extension can perform
BSP specific system termination.

The routines invoked during this will be discussed and their location
in the RTEMS source tree pointed out as we discuss each.

Start Code - Assembly Language Initialization
---------------------------------------------

The assembly language code in the directory ``start`` is the first part
of the application to execute.  It is responsible for initializing the
processor and board enough to execute the rest of the BSP.  This includes:

- initializing the stack

- zeroing out the uninitialized data section ``.bss``

- disabling external interrupts

- copy the initialized data from ROM to RAM

The general rule of thumb is that the start code in assembly should
do the minimum necessary to allow C code to execute to complete the
initialization sequence.

The initial assembly language start code completes its execution by
invoking the shared routine ``boot_card()``.

The label (symbolic name) associated with the starting address of the
program is typically called ``start``.  The start object file is the
first object file linked into the program image so it is ensured that
the start code is at offset 0 in the ``.text`` section.  It is the
responsibility of the linker script in conjunction with the compiler
specifications file to put the start code in the correct location in
the application image.

boot_card() - Boot the Card
---------------------------

The ``boot_card()`` is the first C code invoked.  This file is the
core component in the RTEMS BSP Initialization Framework and provides
the proper sequencing of initialization steps for the BSP, RTEMS and
device drivers. All BSPs use the same shared version of ``boot_card()``
which is located in the following file:
.. code:: c

    c/src/lib/libbsp/shared/bootcard.c

The ``boot_card()`` routine performs the following functions:

- It disables processor interrupts.

- It sets the command line argument variables
  for later use by the application.

- It invokes the BSP specific routine ``bsp_work_area_initialize()``
  which is supposed to initialize the RTEMS Workspace and the C Program Heap.
  Usually the default implementation in``c/src/lib/libbsp/shared/bspgetworkarea.c`` should be sufficient.  Custom
  implementations can use ``bsp_work_area_initialize_default()`` or``bsp_work_area_initialize_with_table()`` available as inline functions from``#include <bsp/bootcard.h>``.

- It invokes the BSP specific routine ``bsp_start()`` which is
  written in C and thus able to perform more advanced initialization.
  Often MMU, bus and interrupt controller initialization occurs here.  Since the
  RTEMS Workspace and the C Program Heap was already initialized by``bsp_work_area_initialize()``, this routine may use ``malloc()``, etc.

- It invokes the RTEMS directive``rtems_initialize_data_structures()`` to initialize the RTEMS
  executive to a state where objects can be created but tasking is not
  enabled.

- It invokes the BSP specific routine ``bsp_libc_init()`` to initialize
  the C Library.  Usually the default implementation in``c/src/lib/libbsp/shared/bsplibc.c`` should be sufficient.

- It invokes the RTEMS directive``rtems_initialize_before_drivers()`` to initialize the MPCI Server
  thread in a multiprocessor configuration and execute API specific
  extensions.

- It invokes the BSP specific routine ``bsp_predriver_hook``. For
  most BSPs, the implementation of this routine does nothing.

- It invokes the RTEMS directive``rtems_initialize_device_drivers()`` to initialize the statically
  configured set of device drivers in the order they were specified in
  the Configuration Table.

- It invokes the BSP specific routine ``bsp_postdriver_hook``. For
  most BSPs, the implementation of this routine does nothing.  However, some
  BSPs use this hook and perform some initialization which must be done at
  this point in the initialization sequence.  This is the last opportunity
  for the BSP to insert BSP specific code into the initialization sequence.

- It invokes the RTEMS directive``rtems_initialize_start_multitasking()``
  which initiates multitasking and performs a context switch to the
  first user application task and may enable interrupts as a side-effect of
  that context switch.  The context switch saves the executing context.  The
  application runs now.  The directive rtems_shutdown_executive() will return
  to the saved context.  The exit() function will use this directive.
  After a return to the saved context a fatal system state is reached.  The
  fatal source is RTEMS_FATAL_SOURCE_EXIT with a fatal code set to the value
  passed to rtems_shutdown_executive().
  The enabling of interrupts during the first context switch is often the source
  for fatal errors during BSP development because the BSP did not clear and/or
  disable all interrupt sources and a spurious interrupt will occur.
  When in the context of the first task but before its body has been
  entered, any C++ Global Constructors will be invoked.

That’s it.  We just went through the entire sequence.

bsp_work_area_initialize() - BSP Specific Work Area Initialization
------------------------------------------------------------------

This is the first BSP specific C routine to execute during system
initialization.  It must initialize the support for allocating memory from the
C Program Heap and RTEMS Workspace commonly referred to as the work areas.
Many BSPs place the work areas at the end of RAM although this is certainly not
a requirement.  Usually the default implementation in:file:`c/src/lib/libbsp/shared/bspgetworkarea.c` should be sufficient.  Custom
implementations can use ``bsp_work_area_initialize_default()`` or``bsp_work_area_initialize_with_table()`` available as inline functions from``#include <bsp/bootcard.h>``.

bsp_start() - BSP Specific Initialization
-----------------------------------------

This is the second BSP specific C routine to execute during system
initialization.  It is called right after ``bsp_work_area_initialize()``.
The ``bsp_start()`` routine often performs required fundamental hardware
initialization such as setting bus controller registers that do not have a
direct impact on whether or not C code can execute.  The interrupt controllers
are usually initialized here.  The source code for this routine is usually
found in the file :file:`c/src/lib/libbsp/${CPU}/${BSP}/startup/bspstart.c`.
It is not allowed to create any operating system objects, e.g. RTEMS
semaphores.

After completing execution, this routine returns to the ``boot_card()``
routine.  In case of errors, the initialization should be terminated via``bsp_fatal()``.

bsp_predriver_hook() - BSP Specific Predriver Hook
--------------------------------------------------

The ``bsp_predriver_hook()`` method is the BSP specific routine that is
invoked immediately before the the device drivers are initialized. RTEMS
initialization is complete but interrupts and tasking are disabled.

The BSP may use the shared version of this routine which is empty.
Most BSPs do not provide a specific implementation of this callback.

Device Driver Initialization
----------------------------

At this point in the initialization sequence, the initialization
routines for all of the device drivers specified in the Device
Driver Table are invoked.  The initialization routines are invoked
in the order they appear in the Device Driver Table.

The Driver Address Table is part of the RTEMS Configuration Table. It
defines device drivers entry points (initialization, open, close, read,
write, and control). For more information about this table, please
refer to the *Configuring a System* chapter in the*RTEMS Application C User’s Guide*.

The RTEMS initialization procedure calls the initialization function for
every driver defined in the RTEMS Configuration Table (this allows
one to include only the drivers needed by the application).

All these primitives have a major and a minor number as arguments:

- the major number refers to the driver type,

- the minor number is used to control two peripherals with the same
  driver (for instance, we define only one major number for the serial
  driver, but two minor numbers for channel A and B if there are two
  channels in the UART).

RTEMS Postdriver Callback
-------------------------

The ``bsp_postdriver_hook()`` BSP specific routine is invoked
immediately after the the device drivers and MPCI are initialized.
Interrupts and tasking are disabled.

Most BSPs use the shared implementation of this routine which is responsible for opening the device ``/dev/console`` for standard input, output and error if the application has configured the Console Device Driver.  This file is located at:
.. code:: c

    c/src/lib/libbsp/shared/bsppost.c

The Interrupt Vector Table
==========================

The Interrupt Vector Table is called different things on different
processor families but the basic functionality is the same.  Each
entry in the Table corresponds to the handler routine for a particular
interrupt source.  When an interrupt from that source occurs, the
specified handler routine is invoked.  Some context information is
saved by the processor automatically when this happens.  RTEMS saves
enough context information so that an interrupt service routine
can be implemented in a high level language.

On some processors, the Interrupt Vector Table is at a fixed address.  If
this address is in RAM, then usually the BSP only has to initialize
it to contain pointers to default handlers.  If the table is in ROM,
then the application developer will have to take special steps to
fill in the table.

If the base address of the Interrupt Vector Table can be dynamically
changed to an arbitrary address, then the RTEMS port to that processor
family will usually allocate its own table and install it.  For example,
on some members of the Motorola MC68xxx family, the Vector Base Register
(``vbr``) contains this base address.

Interrupt Vector Table on the gen68340 BSP
------------------------------------------

The gen68340 BSP provides a default Interrupt Vector Table in the
file ``$BSP_ROOT/start340/start340.s``.  After the ``entry``
label is the definition of space reserved for the table of
interrupts vectors.  This space is assigned the symbolic name
of ``__uhoh`` in the ``gen68340`` BSP.

At ``__uhoh`` label is the default interrupt handler routine. This
routine is only called when an unexpected interrupts is raised.  One can
add their own routine there (in that case there’s a call to a routine -
$BSP_ROOT/startup/dumpanic.c - that prints which address caused the
interrupt and the contents of the registers, stack, etc.), but this should
not return.

Chip Select Initialization
==========================

When the microprocessor accesses a memory area, address decoding is
handled by an address decoder, so that the microprocessor knows which
memory chip(s) to access.   The following figure illustrates this:

.. code:: c

    +-------------------+
    ------------|                   |
    ------------|                   \|------------
    ------------|      Address      \|------------
    ------------|      Decoder      \|------------
    ------------|                   \|------------
    ------------|                   |
    +-------------------+
    CPU Bus                           Chip Select

The Chip Select registers must be programmed such that they match
the ``linkcmds`` settings. In the gen68340 BSP, ROM and RAM
addresses can be found in both the ``linkcmds`` and initialization
code, but this is not a great way to do this.  It is better to
define addresses in the linker script.

Integrated Processor Registers Initialization
=============================================

The CPUs used in many embedded systems are highly complex devices
with multiple peripherals on the CPU itself.  For these devices,
there are always some specific integrated processor registers
that must be initialized.  Refer to the processors’ manuals for
details on these registers and be VERY careful programming them.

Data Section Recopy
===================

The next initialization part can be found in``$BSP340_ROOT/start340/init68340.c``. First the Interrupt
Vector Table is copied into RAM, then the data section recopy is initiated
(_CopyDataClearBSSAndStart in ``$BSP340_ROOT/start340/startfor340only.s``).

This code performs the following actions:

- copies the .data section from ROM to its location reserved in RAM
  (see `Initialized Data`_ for more details about this copy),

- clear ``.bss`` section (all the non-initialized
  data will take value 0).

The RTEMS Configuration Table
=============================

The RTEMS configuration table contains the maximum number of objects RTEMS
can handle during the application (e.g. maximum number of tasks,
semaphores, etc.). It’s used to allocate the size for the RTEMS inner data
structures.

The RTEMS configuration table is application dependent, which means that
one has to provide one per application. It is usually defined by defining
macros and including the header file ``<rtems/confdefs.h>``.  In simple
applications such as the tests provided with RTEMS, it is commonly found
in the main module of the application.  For more complex applications,
it may be in a file by itself.

The header file ``<rtems/confdefs.h>`` defines a constant table
named ``Configuration``.  With RTEMS 4.8 and older, it was accepted
practice for the BSP to copy this table into a modifiable copy named``BSP_Configuration``.  This copy of the table was modified to define
the base address of the RTEMS Executive Workspace as well as to reflect
any BSP and device driver requirements not automatically handled by the
application.  In 4.9 and newer, we have eliminated the BSP copies of the
configuration tables and are making efforts to make the configuration
information generated by ``<rtems/confdefs.h>`` constant and read only.

For more information on the RTEMS Configuration Table, refer to the*RTEMS Application C User’s Guide*.

.. COMMENT: COPYRIGHT (c) 1988-2008.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Console Driver
##############

Introduction
============

This chapter describes the operation of a console driver using
the RTEMS POSIX Termios support.  Traditionally RTEMS has referred
to all serial device drivers as console device drivers.  A
console driver can be used to do raw data processing in addition
to the "normal" standard input and output device functions required
of a console.

The serial driver may be called as the consequence of a C Library
call such as ``printf`` or ``scanf`` or directly via the``read`` or ``write`` system calls.
There are two main functioning modes:

- console: formatted input/output, with special characters (end of
  line, tabulations, etc.) recognition and processing,

- raw: permits raw data processing.

One may think that two serial drivers are needed to handle these two types
of data, but Termios permits having only one driver.

Termios
=======

Termios is a standard for terminal management, included in the POSIX
1003.1b standard.  As part of the POSIX and Open Group Single UNIX
Specification, is commonly provided on UNIX implementations.  The
Open Group has the termios portion of the POSIX standard online
at http://opengroup.org/onlinepubs/007908775/xbd/termios.html.
The requirements for the ``<termios.h>`` file are also provided
and are at http://opengroup.org/onlinepubs/007908775/xsh/termios.h.html.

Having RTEMS support for Termios is beneficial because:

- from the user’s side because it provides standard primitive operations
  to access the terminal and change configuration settings.  These operations
  are the same under UNIX and RTEMS.

- from the BSP developer’s side because it frees the
  developer from dealing with buffer states and mutual exclusions on them.
  Early RTEMS console device drivers also did their own special
  character processing.

- it is part of an internationally recognized standard.

- it makes porting code from other environments easier.

Termios support includes:

- raw and console handling,

- blocking or non-blocking characters receive, with or without
  Timeout.

At this time, RTEMS documentation does not include a thorough discussion
of the Termios functionality.  For more information on Termios,
type ``man termios`` on a Unix box or point a web browser
athttp://www.freebsd.org/cgi/man.cgi.

Driver Functioning Modes
========================

There are generally three main functioning modes for an UART (Universal
Asynchronous Receiver-Transmitter, i.e. the serial chip):

- polled mode

- interrupt driven mode

- task driven mode

In polled mode, the processor blocks on sending/receiving characters.
This mode is not the most efficient way to utilize the UART. But
polled mode is usually necessary when one wants to print an
error message in the event of a fatal error such as a fatal error
in the BSP.  This is also the simplest mode to
program.  Polled mode is generally preferred if the serial port is
to be used primarily as a debug console.  In a simple polled driver,
the software will continuously check the status of the UART when
it is reading or writing to the UART.  Termios improves on this
by delaying the caller for 1 clock tick between successive checks
of the UART on a read operation.

In interrupt driven mode, the processor does not block on sending/receiving
characters.  Data is buffered between the interrupt service routine
and application code.  Two buffers are used to insulate the application
from the relative slowness of the serial device.  One of the buffers is
used for incoming characters, while the other is used for outgoing characters.

An interrupt is raised when a character is received by the UART.
The interrupt subroutine places the incoming character at the end
of the input buffer.  When an application asks for input,
the characters at the front of the buffer are returned.

When the application prints to the serial device, the outgoing characters
are placed at the end of the output buffer.  The driver will place
one or more characters in the UART (the exact number depends on the UART)
An interrupt will be raised when all the characters have been transmitted.
The interrupt service routine has to send the characters
remaining in the output buffer the same way.   When the transmitting side
of the UART is idle, it is typically necessary to prime the transmitter
before the first interrupt will occur.

The task driven mode is similar to interrupt driven mode, but the actual data
processing is done in dedicated tasks instead of interrupt routines.

Serial Driver Functioning Overview
==================================

The following Figure shows how a Termios driven serial driver works:
Figure not included in ASCII version

The following list describes the basic flow.

- the application programmer uses standard C library call (printf,
  scanf, read, write, etc.),

- C library (ctx.g. RedHat (formerly Cygnus) Newlib) calls
  the RTEMS system call interface.  This code can be found in the:file:`cpukit/libcsupport/src` directory.

- Glue code calls the serial driver entry routines.

Basics
------

The low-level driver API changed between RTEMS 4.10 and RTEMS 4.11.  The legacy
callback API is still supported, but its use is discouraged.  The following
functions are deprecated:

- ``rtems_termios_open()`` - use ``rtems_termios_device_open()`` in
  combination with ``rtems_termios_device_install()`` instead.

- ``rtems_termios_close()`` - use ``rtems_termios_device_close()``
  instead.

This manual describes the new API.  A new console driver should consist of
three parts.

# The basic console driver functions using the Termios support.  Add this
  the BSPs Makefile.am:

  .. code:: c

      [...]
      libbsp_a_SOURCES += ../../shared/console-termios.c
      \[...]

# A general serial module specific low-level driver providing the handler
  table for the Termios ``rtems_termios_device_install()`` function.  This
  low-level driver could be used for more than one BSP.

# A BSP specific initialization routine ``console_initialize()``, that
  calls ``rtems_termios_device_install()`` providing a low-level driver
  context for each installed device.

You need to provide a device handler structure for the Termios device
interface.  The functions are described later in this chapter.  The first open
and set attributes handler return a boolean status to indicate success (true)
or failure (false).  The polled read function returns an unsigned character in
case one is available or minus one otherwise.

If you want to use polled IO it should look like the following.  Termios must
be told the addresses of the handler that are to be used for simple character
IO, i.e. pointers to the ``my_driver_poll_read()`` and``my_driver_poll_write()`` functions described later in `Termios and Polled IO`_.

.. code:: c

    const rtems_termios_handler my_driver_handler_polled = {
    .first_open = my_driver_first_open,
    .last_close = my_driver_last_close,
    .poll_read = my_driver_poll_read,
    .write = my_driver_poll_write,
    .set_attributes = my_driver_set_attributes,
    .stop_remote_tx = NULL,
    .start_remote_tx = NULL,
    .mode = TERMIOS_POLLED
    }

For an interrupt driven implementation you need the following.  The driver
functioning is quite different in this mode.  There is no device driver read
handler to be passed to Termios.  Indeed a ``console_read()`` call returns the
contents of Termios input buffer.  This buffer is filled in the driver
interrupt subroutine, see also `Termios and Interrupt Driven IO`_.  The driver 
is responsible for providing a pointer to the``my_driver_interrupt_write()`` function.

.. code:: c

    const rtems_termios_handler my_driver_handler_interrupt = {
    .first_open = my_driver_first_open,
    .last_close = my_driver_last_close,
    .poll_read = NULL,
    .write = my_driver_interrupt_write,
    .set_attributes = my_driver_set_attributes,
    .stopRemoteTx = NULL,
    .stop_remote_tx = NULL,
    .start_remote_tx = NULL,
    .mode = TERMIOS_IRQ_DRIVEN
    };

You can also provide hander for remote transmission control.  This
is not covered in this manual, so they are set to ``NULL`` in the above
examples.

The low-level driver should provide a data structure for its device context.
The initialization routine must provide a context for each installed device via``rtems_termios_device_install()``.  For simplicity of the console
initialization example the device name is also present.  Her is an example header file.
.. code:: c

    #ifndef MY_DRIVER_H
    #define MY_DRIVER_H
    #include <rtems/termiostypes.h>
    #include <some-chip-header.h>
    /* Low-level driver specific data structure \*/
    typedef struct {
    rtems_termios_device_context base;
    const char \*device_name;
    volatile module_register_block \*regs;
    /* More stuff \*/
    } my_driver_context;
    extern const rtems_termios_handler my_driver_handler_polled;
    extern const rtems_termios_handler my_driver_handler_interrupt;
    #endif /* MY_DRIVER_H \*/


Termios and Polled IO
---------------------

The following handler are provided by the low-level driver and invoked by
Termios for simple character IO.

The ``my_driver_poll_write()`` routine is responsible for writing ``n``
characters from ``buf`` to the serial device specified by ``tty``.
.. code:: c

    static void my_driver_poll_write(
    rtems_termios_device_context \*base,
    const char                   \*buf,
    size_t                        n
    )
    {
    my_driver_context \*ctx = (my_driver_context \*) base;
    size_t i;
    /* Write \*/
    for (i = 0; i < n; ++i) {
    my_driver_write_char(ctx, buf[i]);
    }
    }

The ``my_driver_poll_read`` routine is responsible for reading a single
character from the serial device specified by ``tty``.  If no character is
available, then the routine should return minus one.
.. code:: c

    static int my_driver_poll_read(rtems_termios_device_context \*base)
    {
    my_driver_context \*ctx = (my_driver_context \*) base;
    /* Check if a character is available \*/
    if (my_driver_can_read_char(ctx)) {
    /* Return the character \*/
    return my_driver_read_char(ctx);
    } else {
    /* Return an error status \*/
    return -1;
    }
    }

Termios and Interrupt Driven IO
-------------------------------

The UART generally generates interrupts when it is ready to accept or to emit a
number of characters.  In this mode, the interrupt subroutine is the core of
the driver.

The ``my_driver_interrupt_handler()`` is responsible for processing
asynchronous interrupts from the UART.  There may be multiple interrupt
handlers for a single UART.  Some UARTs can generate a unique interrupt vector
for each interrupt source such as a character has been received or the
transmitter is ready for another character.

In the simplest case, the ``my_driver_interrupt_handler()`` will have to check
the status of the UART and determine what caused the interrupt.  The following
describes the operation of an ``my_driver_interrupt_handler`` which has to
do this:
.. code:: c

    static void my_driver_interrupt_handler(
    rtems_vector_number  vector,
    void                \*arg
    )
    {
    rtems_termios_tty \*tty = arg;
    my_driver_context \*ctx = rtems_termios_get_device_context(tty);
    char buf[N];
    size_t n;
    /*
    * Check if we have received something.  The function reads the
    * received characters from the device and stores them in the
    * buffer.  It returns the number of read characters.
    \*/
    n = my_driver_read_received_chars(ctx, buf, N);
    if (n > 0) {
    /* Hand the data over to the Termios infrastructure \*/
    rtems_termios_enqueue_raw_characters(tty, buf, n);
    }
    /*
    * Check if we have something transmitted.  The functions returns
    * the number of transmitted characters since the last write to the
    * device.
    \*/
    n = my_driver_transmitted_chars(ctx);
    if (n > 0) {
    /*
    * Notify Termios that we have transmitted some characters.  It
    * will call now the interrupt write function if more characters
    * are ready for transmission.
    \*/
    rtems_termios_dequeue_characters(tty, n);
    }
    }

The ``my_driver_interrupt_write()`` function is responsible for telling the
device that the ``n`` characters at ``buf`` are to be transmitted.  It
the value ``n`` is zero to indicate that no more characters are to send.
The driver can disable the transmit interrupts now.  This routine is invoked
either from task context with disabled interrupts to start a new transmission
process with exactly one character in case of an idle output state or from the
interrupt handler to refill the transmitter.  If the routine is invoked to
start the transmit process the output state will become busy and Termios starts
to fill the output buffer.  If the transmit interrupt arises before Termios was
able to fill the transmit buffer you will end up with one interrupt per
character.
.. code:: c

    static void my_driver_interrupt_write(
    rtems_termios_device_context  \*base,
    const char                    \*buf,
    size_t                         n
    )
    {
    my_driver_context \*ctx = (my_driver_context \*) base;
    /*
    * Tell the device to transmit some characters from buf (less than
    * or equal to n).  When the device is finished it should raise an
    * interrupt.  The interrupt handler will notify Termios that these
    * characters have been transmitted and this may trigger this write
    * function again.  You may have to store the number of outstanding
    * characters in the device data structure.
    \*/
    /*
    * Termios will set n to zero to indicate that the transmitter is
    * now inactive.  The output buffer is empty in this case.  The
    * driver may disable the transmit interrupts now.
    \*/
    }

Initialization
--------------

The BSP specific driver initialization is called once during the RTEMS
initialization process.

The ``console_initialize()`` function may look like this:
.. code:: c

    #include <my-driver.h>
    #include <rtems/console.h>
    #include <bsp.h>
    #include <bsp/fatal.h>
    static my_driver_context driver_context_table[M] = { /* Some values \*/ };
    rtems_device_driver console_initialize(
    rtems_device_major_number  major,
    rtems_device_minor_number  minor,
    void                      \*arg
    )
    {
    rtems_status_code sc;
    #ifdef SOME_BSP_USE_INTERRUPTS
    const rtems_termios_handler \*handler = &my_driver_handler_interrupt;
    #else
    const rtems_termios_handler \*handler = &my_driver_handler_polled;
    #endif
    /*
    * Initialize the Termios infrastructure.  If Termios has already
    * been initialized by another device driver, then this call will
    * have no effect.
    \*/
    rtems_termios_initialize();
    /* Initialize each device \*/
    for (
    minor = 0;
    minor < RTEMS_ARRAY_SIZE(driver_context_table);
    ++minor
    ) {
    my_driver_context \*ctx = &driver_context_table[minor];
    /*
    * Install this device in the file system and Termios.  In order
    * to use the console (i.e. being able to do printf, scanf etc.
    * on stdin, stdout and stderr), one device must be registered as
    * "/dev/console" (CONSOLE_DEVICE_NAME).
    \*/
    sc = rtems_termios_device_install(
    ctx->device_name,
    major,
    minor,
    handler,
    NULL,
    ctx
    );
    if (sc != RTEMS_SUCCESSFUL) {
    bsp_fatal(SOME_BSP_FATAL_CONSOLE_DEVICE_INSTALL);
    }
    }
    return RTEMS_SUCCESSFUL;
    }

Opening a serial device
-----------------------

The ``console_open()`` function provided by :file:`console-termios.c` is
called whenever a serial device is opened.  The device registered as``"/dev/console"`` (``CONSOLE_DEVICE_NAME``) is opened automatically
during RTEMS initialization.  For instance, if UART channel 2 is registered as``"/dev/tty1"``, the ``console_open()`` entry point will be called as the
result of an ``fopen("/dev/tty1", mode)`` in the application.

During the first open of the device Termios will call the``my_driver_first_open()`` handler.
.. code:: c

    static bool my_driver_first_open(
    rtems_termios_tty             \*tty,
    rtems_termios_device_context  \*base,
    struct termios                \*term,
    rtems_libio_open_close_args_t \*args
    )
    {
    my_driver_context \*ctx = (my_driver_context \*) base;
    rtems_status_code sc;
    bool ok;
    /*
    * You may add some initialization code here.
    \*/
    /*
    * Sets the initial baud rate.  This should be set to the value of
    * the boot loader.  This function accepts only exact Termios baud
    * values.
    \*/
    sc = rtems_termios_set_initial_baud(tty, MY_DRIVER_BAUD_RATE);
    if (sc != RTEMS_SUCCESSFUL) {
    /* Not a valid Termios baud \*/
    }
    /*
    * Alternatively you can set the best baud.
    \*/
    rtems_termios_set_best_baud(term, MY_DRIVER_BAUD_RATE);
    /*
    * To propagate the initial Termios attributes to the device use
    * this.
    \*/
    ok = my_driver_set_attributes(base, term);
    if (!ok) {
    /* This is bad \*/
    }
    /*
    * Return true to indicate a successful set attributes, and false
    * otherwise.
    \*/
    return true;
    }

Closing a Serial Device
-----------------------

The ``console_close()`` provided by :file:`console-termios.c` is invoked when
the serial device is to be closed.  This entry point corresponds to the device
driver close entry point.

Termios will call the ``my_driver_last_close()`` handler if the last close
happens on the device.
.. code:: c

    static void my_driver_last_close(
    rtems_termios_tty             \*tty,
    rtems_termios_device_context  \*base,
    rtems_libio_open_close_args_t \*args
    )
    {
    my_driver_context \*ctx = (my_driver_context \*) base;
    /*
    * The driver may do some cleanup here.
    \*/
    }

Reading Characters from a Serial Device
---------------------------------------

The ``console_read()`` provided by :file:`console-termios.c` is invoked when
the serial device is to be read from.  This entry point corresponds to the
device driver read entry point.

Writing Characters to a Serial Device
-------------------------------------

The ``console_write()`` provided by :file:`console-termios.c` is invoked when
the serial device is to be written to.  This entry point corresponds to the
device driver write entry point.

Changing Serial Line Parameters
-------------------------------

The ``console_control()`` provided by :file:`console-termios.c` is invoked
when the line parameters for a particular serial device are to be changed.
This entry point corresponds to the device driver IO control entry point.

The application writer is able to control the serial line configuration with
Termios calls (such as the ``ioctl()`` command, see the Termios
documentation for more details).  If the driver is to support dynamic
configuration, then it must have the ``console_control()`` piece of code.
Basically ``ioctl()`` commands call ``console_control()`` with the serial
line configuration in a Termios defined data structure.

The driver is responsible for reinitializing the device with the correct
settings.  For this purpose Termios calls the ``my_driver_set_attributes()``
handler.
.. code:: c

    static bool my_driver_set_attributes(
    rtems_termios_device_context \*base,
    const struct termios         \*term
    )
    {
    my_driver_context \*ctx = (my_driver_context \*) base;
    /*
    * Inspect the termios data structure and configure the device
    * appropriately.  The driver should only be concerned with the
    * parts of the structure that specify hardware setting for the
    * communications channel such as baud, character size, etc.
    \*/
    /*
    * Return true to indicate a successful set attributes, and false
    * otherwise.
    \*/
    return true;
    }

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Clock Driver
############

Introduction
============

The purpose of the clock driver is to provide two services for the operating
system.

- A steady time basis to the kernel, so that the RTEMS primitives that need
  a clock tick work properly.  See the *Clock Manager* chapter of the*RTEMS Application C User’s Guide* for more details.

- An optional time counter to generate timestamps of the uptime and wall
  clock time.

The clock driver is usually located in the :file:`clock` directory of the BSP.
Clock drivers should use the :dfn:`Clock Driver Shell` available via the:file:`clockdrv_shell.h` include file.

Clock Driver Shell
==================

The :dfn:`Clock Driver Shell` include file defines the clock driver functions
declared in ``#include <rtems/clockdrv.h>`` which are used by RTEMS
configuration file ``#include <rtems/confdefs.h>``.  In case the application
configuration defines ``#define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER``,
then the clock driver is registered and should provide its services to the
operating system.  A hardware specific clock driver must provide some
functions, defines and macros for the :dfn:`Clock Driver Shell` which are
explained here step by step.  A clock driver file looks in general like this.
.. code:: c

    /*
    * A section with functions, defines and macros to provide hardware specific
    * functions for the Clock Driver Shell.
    \*/
    #include "../../../shared/clockdrv_shell.h"

Initialization
--------------

Depending on the hardware capabilities one out of three clock driver variants
must be selected.

- The most basic clock driver provides only a periodic interrupt service
  routine which calls ``rtems_clock_tick()``.  The interval is determined by
  the application configuration via ``#define
  CONFIGURE_MICROSECONDS_PER_TICK`` and can be obtained via``rtems_configuration_get_microseconds_per_tick()``.  The timestamp
  resolution is limited to the clock tick interval.

- In case the hardware lacks support for a free running counter, then the
  module used for the clock tick may provide support for timestamps with a
  resolution below the clock tick interval.  For this so called simple
  timecounters can be used.

- The desired variant uses a free running counter to provide accurate
  timestamps.  This variant is mandatory on SMP configurations.

Clock Tick Only Variant
~~~~~~~~~~~~~~~~~~~~~~~

.. code:: c

    static void some_support_initialize_hardware( void )
    {
    /* Initialize hardware \*/
    }
    #define Clock_driver_support_initialize_hardware() \\
    some_support_initialize_hardware()
    /* Indicate that this clock driver lacks a proper timecounter in hardware \*/
    #define CLOCK_DRIVER_USE_DUMMY_TIMECOUNTER
    #include "../../../shared/clockdrv_shell.h"

Simple Timecounter Variant
~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code:: c

    #include <rtems/timecounter.h>
    static rtems_timecounter_simple some_tc;
    static uint32_t some_tc_get( rtems_timecounter_simple \*tc )
    {
    return some.counter;
    }
    static bool some_tc_is_pending( rtems_timecounter_simple \*tc )
    {
    return some.is_pending;
    }
    static uint32_t some_tc_get_timecount( struct timecounter \*tc )
    {
    return rtems_timecounter_simple_downcounter_get(
    tc,
    some_tc_get,
    some_tc_is_pending
    );
    }
    static void some_tc_tick( void )
    {
    rtems_timecounter_simple_downcounter_tick( &some_tc, some_tc_get );
    }
    static void some_support_initialize_hardware( void )
    {
    uint32_t frequency = 123456;
    uint64_t us_per_tick = rtems_configuration_get_microseconds_per_tick();
    uint32_t timecounter_ticks_per_clock_tick =
    ( frequency * us_per_tick ) / 1000000;
    /* Initialize hardware \*/
    rtems_timecounter_simple_install(
    &some_tc,
    frequency,
    timecounter_ticks_per_clock_tick,
    some_tc_get_timecount
    );
    }
    #define Clock_driver_support_initialize_hardware() \\
    some_support_initialize_hardware()
    #define Clock_driver_timecounter_tick() \\
    some_tc_tick()
    #include "../../../shared/clockdrv_shell.h"

Timecounter Variant
~~~~~~~~~~~~~~~~~~~

This variant is preferred since it is the most efficient and yields the most
accurate timestamps.  It is also mandatory on SMP configurations to obtain
valid timestamps.  The hardware must provide a periodic interrupt to service
the clock tick and a free running counter for the timecounter.  The free
running counter must have a power of two period.  The ``tc_counter_mask``
must be initialized to the free running counter period minus one, e.g. for a
32-bit counter this is 0xffffffff.  The ``tc_get_timecount`` function must
return the current counter value (the counter values must increase, so if the
counter counts down, a conversion is necessary).  Use``RTEMS_TIMECOUNTER_QUALITY_CLOCK_DRIVER`` for the ``tc_quality``.  Set``tc_frequency`` to the frequency of the free running counter in Hz.  All
other fields of the ``struct timecounter`` must be zero initialized.
Install the initialized timecounter via ``rtems_timecounter_install()``.
.. code:: c

    #include <rtems/timecounter.h>
    static struct timecounter some_tc;
    static uint32_t some_tc_get_timecount( struct timecounter \*tc )
    {
    some.free_running_counter;
    }
    static void some_support_initialize_hardware( void )
    {
    uint64_t us_per_tick = rtems_configuration_get_microseconds_per_tick();
    uint32_t frequency = 123456;
    /*
    * The multiplication must be done in 64-bit arithmetic to avoid an integer
    * overflow on targets with a high enough counter frequency.
    \*/
    uint32_t interval = (uint32_t) ( ( frequency * us_per_tick ) / 1000000 );
    /*
    * Initialize hardware and set up a periodic interrupt for the configuration
    * based interval.
    \*/
    some_tc.tc_get_timecount = some_tc_get_timecount;
    some_tc.tc_counter_mask = 0xffffffff;
    some_tc.tc_frequency = frequency;
    some_tc.tc_quality = RTEMS_TIMECOUNTER_QUALITY_CLOCK_DRIVER;
    rtems_timecounter_install( &some_tc );
    }
    #define Clock_driver_support_initialize_hardware() \\
    some_support_initialize_hardware()
    #include "../../../shared/clockdrv_shell.h"

Install Clock Tick Interrupt Service Routine
--------------------------------------------

The clock driver must provide a function to install the clock tick interrupt
service routine via ``Clock_driver_support_install_isr()``.
.. code:: c

    #include <bsp/irq.h>
    #include <bsp/fatal.h>
    static void some_support_install_isr( rtems_interrupt_handler isr )
    {
    rtems_status_code sc;
    sc = rtems_interrupt_handler_install(
    SOME_IRQ,
    "Clock",
    RTEMS_INTERRUPT_UNIQUE,
    isr,
    NULL
    );
    if ( sc != RTEMS_SUCCESSFUL ) {
    bsp_fatal( SOME_FATAL_IRQ_INSTALL );
    }
    }
    #define Clock_driver_support_install_isr( isr, old ) \\
    some_support_install_isr( isr )
    #include "../../../shared/clockdrv_shell.h"

Support At Tick
---------------

The hardware specific support at tick is specified by``Clock_driver_support_at_tick()``.
.. code:: c

    static void some_support_at_tick( void )
    {
    /* Clear interrupt \*/
    }
    #define Clock_driver_support_at_tick() \\
    some_support_at_tick()
    #include "../../../shared/clockdrv_shell.h"

System Shutdown Support
-----------------------

The :dfn:`Clock Driver Shell` provides the routine ``Clock_exit()`` that is
scheduled to be run during system shutdown via the ``atexit()`` routine.
The hardware specific shutdown support is specified by``Clock_driver_support_shutdown_hardware()`` which is used by``Clock_exit()``.  It should disable the clock tick source if it was
enabled.  This can be used to prevent clock ticks after the system is shutdown.
.. code:: c

    static void some_support_shutdown_hardware( void )
    {
    /* Shutdown hardware \*/
    }
    #define Clock_driver_support_shutdown_hardware() \\
    some_support_shutdown_hardware()
    #include "../../../shared/clockdrv_shell.h"

Multiple Clock Driver Ticks Per Clock Tick
------------------------------------------

In case the hardware needs more than one clock driver tick per clock tick (e.g.
due to a limited range of the hardware timer), then this can be specified with
the optional ``#define CLOCK_DRIVER_ISRS_PER_TICK`` and ``#define
CLOCK_DRIVER_ISRS_PER_TICK_VALUE`` defines.  This is currently used only for x86
and it hopefully remains that way.
.. code:: c

    /* Enable multiple clock driver ticks per clock tick \*/
    #define CLOCK_DRIVER_ISRS_PER_TICK 1
    /* Specifiy the clock driver ticks per clock tick value \*/
    #define CLOCK_DRIVER_ISRS_PER_TICK_VALUE 123
    #include "../../../shared/clockdrv_shell.h"

Clock Driver Ticks Counter
--------------------------

The :dfn:`Clock Driver Shell` provide a global variable that is simply a count
of the number of clock driver interrupt service routines that have occurred.
This information is valuable when debugging a system.  This variable is
declared as follows:
.. code:: c

    volatile uint32_t Clock_driver_ticks;

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Timer Driver
############

The timer driver is primarily used by the RTEMS Timing Tests.
This driver provides as accurate a benchmark timer as possible.
It typically reports its time in microseconds, CPU cycles, or
bus cycles.  This information can be very useful for determining
precisely what pieces of code require optimization and to measure the
impact of specific minor changes.

The gen68340 BSP also uses the Timer Driver to support a high performance
mode of the on-CPU UART.

Benchmark Timer
===============

The RTEMS Timing Test Suite requires a benchmark timer.  The
RTEMS Timing Test Suite is very helpful for determining
the performance of target hardware and comparing its performance
to that of other RTEMS targets.

This section describes the routines which are assumed to exist by
the RTEMS Timing Test Suite.  The names used are *EXACTLY* what
is used in the RTEMS Timing Test Suite so follow the naming convention.

benchmark_timer_initialize
--------------------------

Initialize the timer source.
.. code:: c

    void benchmark_timer_initialize(void)
    {
    initialize the benchmark timer
    }

Read_timer
----------

The ``benchmark_timer_read`` routine returns the number of benchmark
time units (typically microseconds) that have elapsed since the last
call to ``benchmark_timer_initialize``.
.. code:: c

    benchmark_timer_t benchmark_timer_read(void)
    {
    stop time = read the hardware timer
    if the subtract overhead feature is enabled
    subtract overhead from stop time
    return the stop time
    }

Many implementations of this routine subtract the overhead required
to initialize and read the benchmark timer.  This makes the times reported
more accurate.

Some implementations report 0 if the harware timer value change is
sufficiently small.  This is intended to indicate that the execution time
is below the resolution of the timer.

benchmark_timer_disable_subtracting_average_overhead
----------------------------------------------------

This routine is invoked by the "Check Timer" (``tmck``) test in the
RTEMS Timing Test Suite.  It makes the ``benchmark_timer_read``
routine NOT subtract the overhead required
to initialize and read the benchmark timer.  This is used
by the ``tmoverhd`` test to determine the overhead
required to initialize and read the timer.
.. code:: c

    void benchmark_timer_disable_subtracting_average_overhead(bool find_flag)
    {
    disable the subtract overhead feature
    }

The ``benchmark_timer_find_average_overhead`` variable is used to
indicate the state of the "subtract overhead feature".

gen68340 UART FIFO Full Mode
============================

The gen68340 BSP is an example of the use of the timer to support the UART
input FIFO full mode (FIFO means First In First Out and roughly means
buffer). This mode consists in the UART raising an interrupt when n
characters have been received (*n* is the UART’s FIFO length). It results
in a lower interrupt processing time, but the problem is that a scanf
primitive will block on a receipt of less than *n* characters. The solution
is to set a timer that will check whether there are some characters
waiting in the UART’s input FIFO. The delay time has to be set carefully
otherwise high rates will be broken:

- if no character was received last time the interrupt subroutine was
  entered, set a long delay,

- otherwise set the delay to the delay needed for *n* characters
  receipt.

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Real-Time Clock Driver
######################

Introduction
============

The Real-Time Clock (*RTC*) driver is responsible for providing an
interface to an *RTC* device.  \[NOTE: In this chapter, the abbreviation*TOD* is used for *Time of Day*.]  The capabilities provided by this
driver are:

- Set the RTC TOD to RTEMS TOD

- Set the RTEMS TOD to the RTC TOD

- Get the RTC TOD

- Set the RTC TOD to the Specified TOD

- Get the Difference Between the RTEMS and RTC TOD

The reference implementation for a real-time clock driver can
be found in ``c/src/lib/libbsp/shared/tod.c``.  This driver
is based on the libchip concept and can be easily configured
to work with any of the RTC chips supported by the RTC
chip drivers in the directory ``c/src/lib/lib/libchip/rtc``.
There is a README file in this directory for each supported
RTC chip.  Each of these README explains how to configure the
shared libchip implementation of the RTC driver for that particular
RTC chip.

The DY-4 DMV177 BSP used the shared libchip implementation of the RTC
driver.  There were no DMV177 specific configuration routines.  A BSP
could use configuration routines to dynamically determine what type
of real-time clock is on a particular board.  This would be useful for
a BSP supporting multiple board models.  The relevant ports of
the DMV177’s ``RTC_Table`` configuration table is below:
.. code:: c

    #include <bsp.h>
    #include <libchip/rtc.h>
    #include <libchip/icm7170.h>
    bool dmv177_icm7170_probe(int minor);
    rtc_tbl     RTC_Table[] = {
    { "/dev/rtc0",                /* sDeviceName \*/
    RTC_ICM7170,                /* deviceType \*/
    &icm7170_fns,               /* pDeviceFns \*/
    dmv177_icm7170_probe,       /* deviceProbe \*/
    (void \*) ICM7170_AT_1_MHZ,  /* pDeviceParams \*/
    DMV170_RTC_ADDRESS,         /* ulCtrlPort1 \*/
    0,                          /* ulDataPort \*/
    icm7170_get_register_8,     /* getRegister \*/
    icm7170_set_register_8,     /* setRegister \*/
    }
    };
    unsigned long  RTC_Count = (sizeof(RTC_Table)/sizeof(rtc_tbl));
    rtems_device_minor_number  RTC_Minor;
    bool dmv177_icm7170_probe(int minor)
    {
    volatile unsigned16 \*card_resource_reg;
    card_resource_reg = (volatile unsigned16 \*) DMV170_CARD_RESORCE_REG;
    if ( (\*card_resource_reg & DMV170_RTC_INST_MASK) == DMV170_RTC_INSTALLED )
    return TRUE;
    return FALSE;
    }

Initialization
==============

The ``rtc_initialize`` routine is responsible for initializing the
RTC chip so it can be used.  The shared libchip implementation of this
driver supports multiple RTCs and bases its initialization order on
the order the chips are defined in the ``RTC_Table``.  Each chip
defined in the table may or may not be present on this particular board.
It is the responsibility of the ``deviceProbe`` to indicate the
presence of a particular RTC chip.  The first RTC found to be present
is considered the preferred RTC.

In the shared libchip based implementation
of the driver, the following actions are performed:
.. code:: c

    rtems_device_driver rtc_initialize(
    rtems_device_major_number  major,
    rtems_device_minor_number  minor_arg,
    void                      \*arg
    )
    {
    for each RTC configured in RTC_Table
    if the deviceProbe for this RTC indicates it is present
    set RTC_Minor to this device
    set RTC_Present to TRUE
    break out of this loop
    if RTC_Present is not TRUE
    return RTEMS_INVALID_NUMBER to indicate that no RTC is present
    register this minor number as the "/dev/rtc"
    perform the deviceInitialize routine for the preferred RTC chip
    for RTCs past this one in the RTC_Table
    if the deviceProbe for this RTC indicates it is present
    perform the deviceInitialize routine for this RTC chip
    register the configured name for this RTC
    }

The ``deviceProbe`` routine returns TRUE if the device
configured by this entry in the ``RTC_Table`` is present.
This configuration scheme allows one to support multiple versions
of the same board with a single BSP.  For example, if the first
generation of a board had Vendor A’s RTC chip and the second
generation had Vendor B’s RTC chip, RTC_Table could contain
information for both.  The ``deviceProbe`` configured
for Vendor A’s RTC chip would need to return TRUE if the
board was a first generation one.  The ``deviceProbe``
routines are very board dependent and must be provided by
the BSP.

setRealTimeToRTEMS
==================

The ``setRealTimeToRTEMS`` routine sets the current RTEMS TOD to that
of the preferred RTC.
.. code:: c

    void setRealTimeToRTEMS(void)
    {
    if no RTCs are present
    return
    invoke the deviceGetTime routine for the preferred RTC
    set the RTEMS TOD using rtems_clock_set
    }

setRealTimeFromRTEMS
====================

The ``setRealTimeFromRTEMS`` routine sets the preferred RTC TOD to the
current RTEMS TOD.
.. code:: c

    void setRealTimeFromRTEMS(void)
    {
    if no RTCs are present
    return
    obtain the RTEMS TOD using rtems_clock_get
    invoke the deviceSetTime routine for the preferred RTC
    }

getRealTime
===========

The ``getRealTime`` returns the preferred RTC TOD to the
caller.
.. code:: c

    void getRealTime( rtems_time_of_day \*tod )
    {
    if no RTCs are present
    return
    invoke the deviceGetTime routine for the preferred RTC
    }

setRealTime
===========

The ``setRealTime`` routine sets the preferred RTC TOD to the
TOD specified by the caller.
.. code:: c

    void setRealTime( rtems_time_of_day \*tod )
    {
    if no RTCs are present
    return
    invoke the deviceSetTime routine for the preferred RTC
    }

checkRealTime
=============

The ``checkRealTime`` routine returns the number of seconds
difference between the RTC TOD and the current RTEMS TOD.
.. code:: c

    int checkRealTime( void )
    {
    if no RTCs are present
    return -1
    obtain the RTEMS TOD using rtems_clock_get
    get the TOD from the preferred RTC using the deviceGetTime routine
    convert the RTEMS TOD to seconds
    convert the RTC TOD to seconds
    return the RTEMS TOD in seconds - RTC TOD in seconds
    }

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

ATA Driver
##########

Terms
=====

ATA device - physical device attached to an IDE controller

Introduction
============

ATA driver provides generic interface to an ATA device. ATA driver is
hardware independent implementation of ATA standard defined in working draft
"AT Attachment Interface with Extensions (ATA-2)" X3T10/0948D revision 4c,
March 18, 1996. ATA Driver based on IDE Controller Driver and may be used for
computer systems with single IDE controller and with multiple as well. Although
current implementation has several restrictions detailed below ATA driver
architecture allows easily extend the driver. Current restrictions are:

- Only mandatory (see draft p.29) and two optional (READ/WRITE MULTIPLE)
  commands are implemented

- Only PIO mode is supported but both poll and interrupt driven

The reference implementation for ATA driver can be found in``cpukit/libblock/src/ata.c``.

Initialization
==============

The ``ata_initialize`` routine is responsible for ATA driver
initialization. The main goal of the initialization is to detect and
register in the system all ATA devices attached to IDE controllers
successfully initialized by the IDE Controller driver.

In the implementation of the driver, the following actions are performed:
.. code:: c

    rtems_device_driver ata_initialize(
    rtems_device_major_number  major,
    rtems_device_minor_number  minor,
    void                      \*arg
    )
    {
    initialize internal ATA driver data structure
    for each IDE controller successfully initialized by the IDE Controller
    driver
    if the controller is interrupt driven
    set up interrupt handler
    obtain information about ATA devices attached to the controller
    with help of EXECUTE DEVICE DIAGNOSTIC command
    for each ATA device detected on the controller
    obtain device parameters with help of DEVICE IDENTIFY command
    register new ATA device as new block device in the system
    }

Special processing of ATA commands is required because of absence of
multitasking environment during the driver initialization.

Detected ATA devices are registered in the system as physical block devices
(see libblock library description). Device names are formed based on IDE
controller minor number device is attached to and device number on the
controller (0 - Master, 1 - Slave). In current implementation 64 minor
numbers are reserved for each ATA device which allows to support up to 63
logical partitions per device.
.. code:: c

    controller minor    device number    device name    ata device minor
    0                  0             hda                0
    0                  1             hdb               64
    1                  0             hdc              128
    1                  1             hdd              172
    ...                ...            ...

ATA Driver Architecture
=======================

ATA Driver Main Internal Data Structures
----------------------------------------

ATA driver works with ATA requests. ATA request is described by the
following structure:
.. code:: c

    /* ATA request \*/
    typedef struct ata_req_s {
    Chain_Node        link;   /* link in requests chain \*/
    char              type;   /* request type \*/
    ata_registers_t   regs;   /* ATA command \*/
    uint32_t          cnt;    /* Number of sectors to be exchanged \*/
    uint32_t          cbuf;   /* number of current buffer from breq in use \*/
    uint32_t          pos;    /* current position in 'cbuf' \*/
    blkdev_request   \*breq;   /* blkdev_request which corresponds to the
    * ata request
    \*/
    rtems_id          sema;   /* semaphore which is used if synchronous
    * processing of the ata request is required
    \*/
    rtems_status_code status; /* status of ata request processing \*/
    int               error;  /* error code \*/
    } ata_req_t;

ATA driver supports separate ATA requests queues for each IDE
controller (one queue per controller). The following structure contains
information about controller’s queue and devices attached to the controller:
.. code:: c

    /*
    * This structure describes controller state, devices configuration on the
    * controller and chain of ATA requests to the controller.
    \*/
    typedef struct ata_ide_ctrl_s {
    bool          present;   /* controller state \*/
    ata_dev_t     device[2]; /* ata devices description \*/
    Chain_Control reqs;      /* requests chain \*/
    } ata_ide_ctrl_t;

Driver uses array of the structures indexed by the controllers minor
number.

The following structure allows to map an ATA device to the pair (IDE
controller minor number device is attached to, device number
on the controller):
.. code:: c

    /*
    * Mapping of RTEMS ATA devices to the following pairs:
    * (IDE controller number served the device, device number on the controller)
    \*/
    typedef struct ata_ide_dev_s {
    int ctrl_minor;/* minor number of IDE controller serves RTEMS ATA device \*/
    int device;    /* device number on IDE controller (0 or 1) \*/
    } ata_ide_dev_t;

Driver uses array of the structures indexed by the ATA devices minor
number.

ATA driver defines the following internal events:
.. code:: c

    /* ATA driver events \*/
    typedef enum ata_msg_type_s {
    ATA_MSG_GEN_EVT = 1,     /* general event \*/
    ATA_MSG_SUCCESS_EVT,     /* success event \*/
    ATA_MSG_ERROR_EVT,       /* error event \*/
    ATA_MSG_PROCESS_NEXT_EVT /* process next ata request event \*/
    } ata_msg_type_t;

Brief ATA Driver Core Overview
------------------------------

All ATA driver functionality is available via ATA driver ioctl. Current
implementation supports only two ioctls: BLKIO_REQUEST and
ATAIO_SET_MULTIPLE_MODE. Each ATA driver ioctl() call generates an
ATA request which is appended to the appropriate controller queue depending
on ATA device the request belongs to. If appended request is single request in
the controller’s queue then ATA driver event is generated.

ATA driver task which manages queue of ATA driver events is core of ATA
driver. In current driver version queue of ATA driver events implemented
as RTEMS message queue. Each message contains event type, IDE controller
minor number on which event happened and error if an error occurred. Events
may be generated either by ATA driver ioctl call or by ATA driver task itself.
Each time ATA driver task receives an event it gets controller minor number
from event, takes first ATA request from controller queue and processes it
depending on request and event types. An ATA request processing may also
includes sending of several events. If ATA request processing is finished
the ATA request is removed from the controller queue. Note, that in current
implementation maximum one event per controller may be queued at any moment
of the time.

(This part seems not very clear, hope I rewrite it soon)

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

IDE Controller Driver
#####################

Introduction
============

The IDE Controller driver is responsible for providing an
interface to an IDE Controller.  The capabilities provided by this
driver are:

- Read IDE Controller register

- Write IDE Controller register

- Read data block through IDE Controller Data Register

- Write data block through IDE Controller Data Register

The reference implementation for an IDE Controller driver can
be found in ``$RTEMS_SRC_ROOT/c/src/libchip/ide``. This driver
is based on the libchip concept and allows to work with any of the IDE
Controller chips simply by appropriate configuration of BSP. Drivers for a
particular IDE Controller chips locate in the following directories: drivers
for well-known IDE Controller chips locate into``$RTEMS_SRC_ROOT/c/src/libchip/ide``, drivers for IDE Controller chips
integrated with CPU locate into``$RTEMS_SRC_ROOT/c/src/lib/libcpu/myCPU`` and
drivers for custom IDE Controller chips (for example, implemented on FPGA)
locate into ``$RTEMS_SRC_ROOT/c/src/lib/libbsp/myBSP``.
There is a README file in these directories for each supported
IDE Controller chip. Each of these README explains how to configure a BSP
for that particular IDE Controller chip.

Initialization
==============

IDE Controller chips used by a BSP are statically configured into``IDE_Controller_Table``. The ``ide_controller_initialize`` routine is
responsible for initialization of all configured IDE controller chips.
Initialization order of the chips based on the order the chips are defined in
the ``IDE_Controller_Table``.

The following actions are performed by the IDE Controller driver
initialization routine:
.. code:: c

    rtems_device_driver ide_controller_initialize(
    rtems_device_major_number  major,
    rtems_device_minor_number  minor_arg,
    void                      \*arg
    )
    {
    for each IDE Controller chip configured in IDE_Controller_Table
    if (BSP dependent probe(if exists) AND device probe for this IDE chip
    indicates it is present)
    perform initialization of the particular chip
    register device with configured name for this chip
    }

Read IDE Controller Register
============================

The ``ide_controller_read_register`` routine reads the content of the IDE
Controller chip register. IDE Controller chip is selected via the minor
number. This routine is not allowed to be called from an application.
.. code:: c

    void ide_controller_read_register(rtems_device_minor_number minor,
    unsigned32 reg, unsigned32 \*value)
    {
    get IDE Controller chip configuration information from
    IDE_Controller_Table by minor number
    invoke read register routine for the chip
    }

Write IDE Controller Register
=============================

The ``ide_controller_write_register`` routine writes IDE Controller chip
register with specified value. IDE Controller chip is selected via the minor
number. This routine is not allowed to be called from an application.
.. code:: c

    void ide_controller_write_register(rtems_device_minor_number minor,
    unsigned32 reg, unsigned32 value)
    {
    get IDE Controller chip configuration information from
    IDE_Controller_Table by minor number
    invoke write register routine for the chip
    }

Read Data Block Through IDE Controller Data Register
====================================================

The ``ide_controller_read_data_block`` provides multiple consequent read
of the IDE Controller Data Register. IDE Controller chip is selected via the
minor number. The same functionality may be achieved via separate multiple
calls of ``ide_controller_read_register`` routine but``ide_controller_read_data_block`` allows to escape functions call
overhead. This routine is not allowed to be called from an application.
.. code:: c

    void ide_controller_read_data_block(
    rtems_device_minor_number  minor,
    unsigned16                 block_size,
    blkdev_sg_buffer          \*bufs,
    uint32_t                  \*cbuf,
    uint32_t                  \*pos
    )
    {
    get IDE Controller chip configuration information from
    IDE_Controller_Table by minor number
    invoke read data block routine for the chip
    }

Write Data Block Through IDE Controller Data Register
=====================================================

The ``ide_controller_write_data_block`` provides multiple consequent write
into the IDE Controller Data Register. IDE Controller chip is selected via the
minor number. The same functionality may be achieved via separate multiple
calls of ``ide_controller_write_register`` routine but``ide_controller_write_data_block`` allows to escape functions call
overhead. This routine is not allowed to be called from an application.
.. code:: c

    void ide_controller_write_data_block(
    rtems_device_minor_number  minor,
    unsigned16                 block_size,
    blkdev_sg_buffer          \*bufs,
    uint32_t                  \*cbuf,
    uint32_t                  \*pos
    )
    {
    get IDE Controller chip configuration information from
    IDE_Controller_Table by minor number
    invoke write data block routine for the chip
    }

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Non-Volatile Memory Driver
##########################

The Non-Volatile driver is responsible for providing an
interface to various types of non-volatile memory.  These
types of memory include, but are not limited to, Flash, EEPROM,
and battery backed RAM.  The capabilities provided
by this class of device driver are:

- Initialize the Non-Volatile Memory Driver

- Optional Disable Read and Write Handlers

- Open a Particular Memory Partition

- Close a Particular Memory Partition

- Read from a Particular Memory Partition

- Write to a Particular Memory Partition

- Erase the Non-Volatile Memory Area

There is currently only one non-volatile device driver included in the
RTEMS source tree.  The information provided in this chapter
is based on drivers developed for applications using RTEMS.
It is hoped that this driver model information can form the
basis for a standard non-volatile memory driver model that
can be supported in future RTEMS distribution.

Major and Minor Numbers
=======================

The *major* number of a device driver is its index in the
RTEMS Device Address Table.

A *minor* number is associated with each device instance
managed by a particular device driver.  An RTEMS minor number
is an ``unsigned32`` entity.  Convention calls
dividing the bits in the minor number down into categories
that specify an area of non-volatile memory and a partition
with that area.  This results in categories
like the following:

- *area* - indicates a block of non-volatile memory

- *partition* - indicates a particular address range with an area

From the above, it should be clear that a single device driver
can support multiple types of non-volatile memory in a single system.
The minor number is used to distinguish the types of memory and
blocks of memory used for different purposes.

Non-Volatile Memory Driver Configuration
========================================

There is not a standard non-volatile driver configuration table but some
fields are common across different drivers.  The non-volatile memory driver
configuration table is typically an array of structures with each
structure containing the information for a particular area of
non-volatile memory.
The following is a list of the type of information normally required
to configure each area of non-volatile memory.

*memory_type*
    is the type of memory device in this area.  Choices are battery backed RAM,
    EEPROM, Flash, or an optional user-supplied type.  If the user-supplied type
    is configured, then the user is responsible for providing a set of
    routines to program the memory.

*memory*
    is the base address of this memory area.

*attributes*
    is a pointer to a memory type specific attribute block.  Some of
    the fields commonly contained in this memory type specific attribute
    structure area:

    *use_protection_algorithm*

        is set to TRUE to indicate that the protection (i.e. locking) algorithm
        should be used for this area of non-volatile memory.  A particular
        type of non-volatile memory may not have a protection algorithm.

    *access*

        is an enumerated type to indicate the organization of the memory
        devices in this memory area.  The following is a list of the
        access types supported by the current driver implementation:
        - simple unsigned8
        - simple unsigned16
        - simple unsigned32
        - simple unsigned64
        - single unsigned8 at offset 0 in an unsigned16
        - single unsigned8 at offset 1 in an unsigned16
        - single unsigned8 at offset 0 in an unsigned32
        - single unsigned8 at offset 1 in an unsigned32
        - single unsigned8 at offset 2 in an unsigned32
        - single unsigned8 at offset 3 in an unsigned32

    *depth*

        is the depth of the progamming FIFO on this particular chip.  Some
        chips, particularly EEPROMs, have the same programming algorithm but
        vary in the depth of the amount of data that can be programmed in a single
        block.

*number_of_partitions*
    is the number of logical partitions within this area.

*Partitions*
    is the address of the table that contains an entry to describe each
    partition in this area.  Fields within each element of this
    table are defined as follows:

    *offset*

        is the offset of this partition from the base address of this area.

    *length*

        is the length of this partition.

By dividing an area of memory into multiple partitions, it is possible
to easily divide the non-volatile memory for different purposes.

Initialize the Non-Volatile Memory Driver
=========================================

At system initialization, the non-volatile memory driver’s
initialization entry point will be invoked.  As part of
initialization, the driver will perform
whatever initializatin is required on each non-volatile memory area.

The discrete I/O driver may register device names for memory
partitions of particular interest to the system.  Normally this
will be restricted to the device "/dev/nv_memory" to indicate
the entire device driver.

Disable Read and Write Handlers
===============================

Depending on the target’s non-volatile memory configuration, it may be
possible to write to a status register and make the memory area completely
inaccessible.  This is target dependent and beyond the standard capabilities
of any memory type.  The user has the optional capability to provide
handlers to disable and enable access to a partiticular memory area.

Open a Particular Memory Partition
==================================

This is the driver open call.  Usually this call does nothing other than
validate the minor number.

With some drivers, it may be necessary to allocate memory when a particular
device is opened.  If that is the case, then this is often the place
to do this operation.

Close a Particular Memory Partition
===================================

This is the driver close call.  Usually this call does nothing.

With some drivers, it may be necessary to allocate memory when a particular
device is opened.  If that is the case, then this is the place
where that memory should be deallocated.

Read from a Particular Memory Partition
=======================================

This corresponds to the driver read call.  After validating the minor
number and arguments, this call enables reads from the specified
memory area by invoking the user supplied "enable reads handler"
and then reads the indicated memory area.  When
invoked the ``argument_block`` is actually a pointer to the following
structure type:
.. code:: c

    typedef struct {
    uint32_t  offset;
    void     \*buffer;
    uint32_t  length;
    uint32_t  status;
    }   Non_volatile_memory_Driver_arguments;

The driver reads ``length`` bytes starting at ``offset`` into
the partition and places them at ``buffer``.  The result is returned
in ``status``.

After the read operation is complete, the user supplied "disable reads handler"
is invoked to protect the memory area again.

Write to a Particular Memory Partition
======================================

This corresponds to the driver write call.   After validating the minor
number and arguments, this call enables writes to the specified
memory area by invoking the "enable writes handler", then unprotecting
the memory area, and finally actually writing to the indicated memory
area.  When invoked the ``argument_block`` is actually a pointer to
the following structure type:
.. code:: c

    typedef struct {
    uint32_t   offset;
    void      \*buffer;
    uint32_t   length;
    uint32_t   status;
    }   Non_volatile_memory_Driver_arguments;

The driver writes ``length`` bytes from ``buffer`` and
writes them to the non-volatile memory starting at ``offset`` into
the partition.  The result is returned in ``status``.

After the write operation is complete, the "disable writes handler"
is invoked to protect the memory area again.

Erase the Non-Volatile Memory Area
==================================

This is one of the IOCTL functions supported by the I/O control
device driver entry point.  When this IOCTL function is invoked,
the specified area of non-volatile memory is erased.

.. COMMENT: Written by Eric Norum

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Networking Driver
#################

Introduction
============

This chapter is intended to provide an introduction to the
procedure for writing RTEMS network device drivers.
The example code is taken from the ‘Generic 68360’ network device
driver.  The source code for this driver is located in the``c/src/lib/libbsp/m68k/gen68360/network`` directory in the RTEMS
source code distribution.  Having a copy of this driver at
hand when reading the following notes will help significantly.

Learn about the network device
==============================

Before starting to write the network driver become completely
familiar with the programmer’s view of the device.
The following points list some of the details of the
device that must be understood before a driver can be written.

- Does the device use DMA to transfer packets to and from
  memory or does the processor have to
  copy packets to and from memory on the device?

- If the device uses DMA, is it capable of forming a single
  outgoing packet from multiple fragments scattered in separate
  memory buffers?

- If the device uses DMA, is it capable of chaining multiple
  outgoing packets, or does each outgoing packet require
  intervention by the driver?

- Does the device automatically pad short frames to the minimum
  64 bytes or does the driver have to supply the padding?

- Does the device automatically retry a transmission on detection
  of a collision?

- If the device uses DMA, is it capable of buffering multiple
  packets to memory, or does the receiver have to be restarted
  after the arrival of each packet?

- How are packets that are too short, too long, or received with
  CRC errors handled?  Does the device automatically continue
  reception or does the driver have to intervene?

- How is the device Ethernet address set?  How is the device
  programmed to accept or reject broadcast and multicast packets?

- What interrupts does the device generate?  Does it generate an
  interrupt for each incoming packet, or only for packets received
  without error?  Does it generate an interrupt for each packet
  transmitted, or only when the transmit queue is empty?  What
  happens when a transmit error is detected?

In addition, some controllers have specific questions regarding
board specific configuration.  For example, the SONIC Ethernet
controller has a very configurable data bus interface.  It can
even be configured for sixteen and thirty-two bit data buses.  This
type of information should be obtained from the board vendor.

Understand the network scheduling conventions
=============================================

When writing code for the driver transmit and receive tasks,
take care to follow the network scheduling conventions.  All tasks
which are associated with networking share various
data structures and resources.  To ensure the consistency
of these structures the tasks
execute only when they hold the network semaphore (``rtems_bsdnet_semaphore``).
The transmit and receive tasks must abide by this protocol.  Be very
careful to avoid ‘deadly embraces’ with the other network tasks.
A number of routines are provided to make it easier for the network
driver code to conform to the network task scheduling conventions.

- ``void rtems_bsdnet_semaphore_release(void)``
  This function releases the network semaphore.
  The network driver tasks must call this function immediately before
  making any blocking RTEMS request.

- ``void rtems_bsdnet_semaphore_obtain(void)``
  This function obtains the network semaphore.
  If a network driver task has released the network semaphore to allow other
  network-related tasks to run while the task blocks, then this function must
  be called to reobtain the semaphore immediately after the return from the
  blocking RTEMS request.

- ``rtems_bsdnet_event_receive(rtems_event_set, rtems_option, rtems_interval, rtems_event_set \*)``
  The network driver task should call this function when it wishes to wait
  for an event.  This function releases the network semaphore,
  calls ``rtems_event_receive`` to wait for the specified event
  or events and reobtains the semaphore.
  The value returned is the value returned by the ``rtems_event_receive``.

Network Driver Makefile
=======================

Network drivers are considered part of the BSD network package and as such
are to be compiled with the appropriate flags.  This can be accomplished by
adding ``-D__INSIDE_RTEMS_BSD_TCPIP_STACK__`` to the ``command line``.
If the driver is inside the RTEMS source tree or is built using the
RTEMS application Makefiles, then adding the following line accomplishes
this:

.. code:: c

    DEFINES += -D__INSIDE_RTEMS_BSD_TCPIP_STACK__

This is equivalent to the following list of definitions.  Early versions
of the RTEMS BSD network stack required that all of these be defined.

.. code:: c

    -D_COMPILING_BSD_KERNEL_ -DKERNEL -DINET -DNFS \\
    -DDIAGNOSTIC -DBOOTP_COMPAT

Defining these macros tells the network header files that the driver
is to be compiled with extended visibility into the network stack.  This
is in sharp contrast to applications that simply use the network stack.
Applications do not require this level of visibility and should stick
to the portable application level API.

As a direct result of being logically internal to the network stack,
network drivers use the BSD memory allocation routines   This means,
for example, that malloc takes three arguments.  See the SONIC
device driver (``c/src/lib/libchip/network/sonic.c``) for an example
of this.  Because of this, network drivers should not include``<stdlib.h>``.  Doing so will result in conflicting definitions
of ``malloc()``.

*Application level* code including network servers such as the FTP
daemon are *not* part of the BSD kernel network code and should not be
compiled with the BSD network flags.  They should include``<stdlib.h>`` and not define the network stack visibility
macros.

Write the Driver Attach Function
================================

The driver attach function is responsible for configuring the driver
and making the connection between the network stack
and the driver.

Driver attach functions take a pointer to an``rtems_bsdnet_ifconfig`` structure as their only argument.
and set the driver parameters based on the
values in this structure.  If an entry in the configuration
structure is zero the attach function chooses an
appropriate default value for that parameter.

The driver should then set up several fields in the ifnet structure
in the device-dependent data structure supplied and maintained by the driver:

``ifp->if_softc``
    Pointer to the device-dependent data.  The first entry
    in the device-dependent data structure must be an ``arpcom``
    structure.

``ifp->if_name``
    The name of the device.  The network stack uses this string
    and the device number for device name lookups.  The device name should
    be obtained from the ``name`` entry in the configuration structure.

``ifp->if_unit``
    The device number.  The network stack uses this number and the
    device name for device name lookups.  For example, if``ifp->if_name`` is ‘``scc``’ and ``ifp->if_unit`` is ‘``1``’,
    the full device name would be ‘``scc1``’.  The unit number should be
    obtained from the ‘name’ entry in the configuration structure.

``ifp->if_mtu``
    The maximum transmission unit for the device.  For Ethernet
    devices this value should almost always be 1500.

``ifp->if_flags``
    The device flags.  Ethernet devices should set the flags
    to ``IFF_BROADCAST|IFF_SIMPLEX``, indicating that the
    device can broadcast packets to multiple destinations
    and does not receive and transmit at the same time.

``ifp->if_snd.ifq_maxlen``
    The maximum length of the queue of packets waiting to be
    sent to the driver.  This is normally set to ``ifqmaxlen``.

``ifp->if_init``
    The address of the driver initialization function.

``ifp->if_start``
    The address of the driver start function.

``ifp->if_ioctl``
    The address of the driver ioctl function.

``ifp->if_output``
    The address of the output function.  Ethernet devices
    should set this to ``ether_output``.

RTEMS provides a function to parse the driver name in the
configuration structure into a device name and unit number.
.. code:: c

    int rtems_bsdnet_parse_driver_name (
    const struct rtems_bsdnet_ifconfig \*config,
    char \**namep
    );

The function takes two arguments; a pointer to the configuration
structure and a pointer to a pointer to a character.  The function
parses the configuration name entry, allocates memory for the driver
name, places the driver name in this memory, sets the second argument
to point to the name and returns the unit number.
On error, a message is printed and -1 is returned.

Once the attach function  has set up the above entries it must link the
driver data structure onto the list of devices by
calling ``if_attach``.  Ethernet devices should then
call ``ether_ifattach``.  Both functions take a pointer to the
device’s ``ifnet`` structure as their only argument.

The attach function should return a non-zero value to indicate that
the driver has been successfully configured and attached.

Write the Driver Start Function.
================================

This function is called each time the network stack wants to start the
transmitter.  This occures whenever the network stack adds a packet
to a device’s send queue and the ``IFF_OACTIVE`` bit in the
device’s ``if_flags`` is not set.

For many devices this function need only set the ``IFF_OACTIVE`` bit in the``if_flags`` and send an event to the transmit task
indicating that a packet is in the driver transmit queue.

Write the Driver Initialization Function.
=========================================

This function should initialize the device, attach to interrupt handler,
and start the driver transmit and receive tasks.  The function
.. code:: c

    rtems_id
    rtems_bsdnet_newproc (char \*name,
    int stacksize,
    void(\*entry)(void \*),
    void \*arg);

should be used to start the driver tasks.

Note that the network stack may call the driver initialization function more
than once.
Make sure multiple versions of the receive and transmit tasks are not accidentally
started.

Write the Driver Transmit Task
==============================

This task is reponsible for removing packets from the driver send queue and sending them to the device.  The task should block waiting for an event from the
driver start function indicating that packets are waiting to be transmitted.
When the transmit task has drained the driver send queue the task should clear
the ``IFF_OACTIVE`` bit in ``if_flags`` and block until another outgoing
packet is queued.

Write the Driver Receive Task
=============================

This task should block until a packet arrives from the device.  If the
device is an Ethernet interface the function ``ether_input`` should be called
to forward the packet to the network stack.   The arguments to ``ether_input``
are a pointer to the interface data structure, a pointer to the ethernet
header and a pointer to an mbuf containing the packet itself.

Write the Driver Interrupt Handler
==================================

A typical interrupt handler will do nothing more than the hardware
manipulation required to acknowledge the interrupt and send an RTEMS event
to wake up the driver receive or transmit task waiting for the event.
Network interface interrupt handlers must not make any calls to other
network routines.

Write the Driver IOCTL Function
===============================

This function handles ioctl requests directed at the device.  The ioctl
commands which must be handled are:

``SIOCGIFADDR``

``SIOCSIFADDR``

    If the device is an Ethernet interface these
    commands should be passed on to ``ether_ioctl``.

``SIOCSIFFLAGS``

    This command should be used to start or stop the device,
    depending on the state of the interface ``IFF_UP`` and``IFF_RUNNING`` bits in ``if_flags``:

    ``IFF_RUNNING``

        Stop the device.

    ``IFF_UP``

        Start the device.

    ``IFF_UP|IFF_RUNNING``

        Stop then start the device.

    ``0``

        Do nothing.

Write the Driver Statistic-Printing Function
============================================

This function should print the values of any statistic/diagnostic
counters the network driver may use.  The driver ioctl function should call
the statistic-printing function when the ioctl command is``SIO_RTEMS_SHOW_STATS``.

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Shared Memory Support Driver
############################

The Shared Memory Support Driver is responsible for providing glue
routines and configuration information required by the Shared
Memory Multiprocessor Communications Interface (MPCI).  The
Shared Memory Support Driver tailors the portable Shared
Memory Driver to a particular target platform.

This driver is only required in shared memory multiprocessing
systems that use the RTEMS mulitprocessing support.  For more
information on RTEMS multiprocessing capabilities and the
MPCI, refer to the *Multiprocessing Manager* chapter
of the *RTEMS Application C User’s Guide*.

Shared Memory Configuration Table
=================================

The Shared Memory Configuration Table is defined in the following
structure:
.. code:: c

    typedef volatile uint32_t vol_u32;
    typedef struct {
    vol_u32 \*address;        /* write here for interrupt    \*/
    vol_u32  value;          /* this value causes interrupt \*/
    vol_u32  length;         /* for this length (0,1,2,4)   \*/
    } Shm_Interrupt_information;
    struct shm_config_info {
    vol_u32           \*base;       /* base address of SHM         \*/
    vol_u32            length;     /* length (in bytes) of SHM    \*/
    vol_u32            format;     /* SHM is big or little endian \*/
    vol_u32          (\*convert)(); /* neutral conversion routine  \*/
    vol_u32            poll_intr;  /* POLLED or INTR driven mode  \*/
    void             (\*cause_intr)( uint32_t );
    Shm_Interrupt_information   Intr; /* cause intr information   \*/
    };
    typedef struct shm_config_info shm_config_table;

where the fields are defined as follows:

*base*
    is the base address of the shared memory buffer used to pass
    messages between the nodes in the system.

*length*
    is the length (in bytes) of the shared memory buffer used to pass
    messages between the nodes in the system.

*format*
    is either SHM_BIG or SHM_LITTLE to indicate that the neutral format
    of the shared memory area is big or little endian.  The format
    of the memory should be chosen to match most of the inter-node traffic.

*convert*
    is the address of a routine which converts from native format to
    neutral format.   Ideally, the neutral format is the same as the
    native format so this routine is quite simple.

*poll_intr*
    is either INTR_MODE or POLLED_MODE to indicate how the node will be
    informed of incoming messages.

*cause_intr*

*Intr*

    is the information required to cause an interrupt on a node.  This
    structure contains the following fields:

    *address*

        is the address to write at to cause an interrupt on that node.
        For a polled node, this should be NULL.

    *value*

        is the value to write to cause an interrupt.

    *length*

        is the length of the entity to write on the node to cause an interrupt.
        This can be 0 to indicate polled operation, 1 to write a byte, 2 to
        write a sixteen-bit entity, and 4 to write a thirty-two bit entity.

Primitives
==========

Convert Address
---------------

The ``Shm_Convert_address`` is responsible for converting an address
of an entity in the shared memory area into the address that should be
used from this node.  Most targets will simply return the address
passed to this routine.  However, some target boards will have a special
window onto the shared memory.  For example, some VMEbus boards have
special address windows to access addresses that are normally reserved
in the CPU’s address space.
.. code:: c

    void \*Shm_Convert_address( void \*address )
    {
    return the local address version of this bus address
    }

Get Configuration
-----------------

The ``Shm_Get_configuration`` routine is responsible for filling in the
Shared Memory Configuration Table passed to it.
.. code:: c

    void Shm_Get_configuration(
    uint32_t           localnode,
    shm_config_table \**shmcfg
    )
    {
    fill in the Shared Memory Configuration Table
    }

Locking Primitives
------------------

This is a collection of routines that are invoked by the portable
part of the Shared Memory Driver to manage locks in the shared
memory buffer area.  Accesses to the shared memory must be
atomic.  Two nodes in a multiprocessor system must not be manipulating
the shared data structures simultaneously.  The locking primitives
are used to insure this.

To avoid deadlock, local processor interrupts should be disabled the entire
time the locked queue is locked.

The locking primitives operate on the lock``field`` of the ``Shm_Locked_queue_Control``
data structure.  This structure is defined as follows:
.. code:: c

    typedef struct {
    vol_u32 lock;  /* lock field for this queue    \*/
    vol_u32 front; /* first envelope on queue      \*/
    vol_u32 rear;  /* last envelope on queue       \*/
    vol_u32 owner; /* receiving (i.e. owning) node \*/
    } Shm_Locked_queue_Control;

where each field is defined as follows:

*lock*
    is the lock field.  Every node in the system must agree on how this
    field will be used.  Many processor families provide an atomic
    "test and set" instruction that is used to manage this field.

*front*
    is the index of the first message on this locked queue.

*rear*
    is the index of the last message on this locked queue.

*owner*
    is the node number of the node that currently has this structure locked.

Initializing a Shared Lock
~~~~~~~~~~~~~~~~~~~~~~~~~~

The ``Shm_Initialize_lock`` routine is responsible for
initializing the lock field.  This routines usually is implemented
as follows:
.. code:: c

    void Shm_Initialize_lock(
    Shm_Locked_queue_Control \*lq_cb
    )
    {
    lq_cb->lock = LQ_UNLOCKED;
    }

Acquiring a Shared Lock
~~~~~~~~~~~~~~~~~~~~~~~

The ``Shm_Lock`` routine is responsible for
acquiring the lock field.  Interrupts should be
disabled while that lock is acquired.  If the lock
is currently unavailble, then the locking routine
should delay a few microseconds to allow the other
node to release the lock.  Doing this reduces bus contention
for the lock.  This routines usually is implemented as follows:
.. code:: c

    void Shm_Lock(
    Shm_Locked_queue_Control \*lq_cb
    )
    {
    disable processor interrupts
    set Shm_isrstat to previous interrupt disable level
    while ( TRUE ) {
    atomically attempt to acquire the lock
    if the lock was acquired
    return
    delay some small period of time
    }
    }

Releasing a Shared Lock
~~~~~~~~~~~~~~~~~~~~~~~

The ``Shm_Unlock`` routine is responsible for
releasing the lock field and reenabling processor
interrupts.  This routines usually is implemented as follows:
.. code:: c

    void Shm_Unlock(
    Shm_Locked_queue_Control \*lq_cb
    )
    {
    set the lock to the unlocked value
    reenable processor interrupts to their level prior
    to the lock being acquired.  This value was saved
    in the global variable Shm_isrstat
    }

Installing the MPCI ISR
=======================

The ``Shm_setvec`` is invoked by the portable portion
of the shared memory to install the interrupt service routine
that is invoked when an incoming message is announced.  Some
target boards support an interprocessor interrupt or mailbox
scheme and this is where the ISR for that interrupt would be
installed.

On an interrupt driven node, this routine would be implemented
as follows:
.. code:: c

    void Shm_setvec( void )
    {
    install the interprocessor communications ISR
    }

On a polled node, this routine would be empty.

.. COMMENT: COPYRIGHT (c) 1988-2009.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Frame Buffer Driver
###################

In this chapter, we present the basic functionality implemented by a
frame buffer driver: ``frame_buffer_initialize()``, ``frame_buffer_open()``,``frame_buffer_close()``, ``frame_buffer_read()``, ``frame_buffer_write()``
and ``frame_buffer_control()``.

Introduction
============

The purpose of the frame buffer driver is to provide an abstraction for
graphics hardware.
By using the frame buffer interface, an application can display graphics
without knowing anything about the low-level details of interfacing to a
particular graphics adapter. The parameters governing the mapping of
memory to displayed pixels (planar or linear, bit depth, etc) is still
implementation-specific, but device-independent methods are provided to
determine and potentially modify these parameters.

The frame buffer driver is commonly located in the ``console``
directory of the BSP and registered by the name */dev/fb0*.
Additional frame buffers (if available) are named */dev/fb1*,*/dev/fb2*, etc.

To work with the frame buffer, the following operation sequence is used:``open()``, ``ioctls()`` to get the frame buffer info, ``read()`` and/or``write()``, and ``close()``.

Driver Function Overview
========================

Initialization
--------------

The driver initialization is called once during the RTEMS initialization
process and returns RTEMS_SUCCESSFUL when the device driver is successfully
initialized. During the initialization, a name is assigned to the frame
buffer device.  If the graphics hardware supports console text output,
as is the case with the pc386 VGA hardware, initialization into graphics
mode may be deferred until the device is ``open()`` ed.

The ``frame_buffer_initialize()`` function may look like this:

.. code:: c

    rtems_device_driver frame_buffer_initialize(
    rtems_device_major_number  major,
    rtems_device_minor_number  minor,
    void                      \*arg)
    {
    rtems_status_code status;
    printk( "frame buffer driver initializing..\\n" );
    /*
    * Register the device
    \*/
    status = rtems_io_register_name("/dev/fb0", major, 0);
    if (status != RTEMS_SUCCESSFUL)
    {
    printk("Error registering frame buffer device!\\n");
    rtems_fatal_error_occurred( status );
    }
    /*
    * graphics hardware initialization goes here for non-console
    * devices
    \*/
    return RTEMS_SUCCESSFUL;
    }

Opening the Frame Buffer Device
-------------------------------

The ``frame_buffer_open()`` function is called whenever a frame buffer device is opened.
If the frame buffer is registered as "/dev/fb0", the ``frame_buffer_open`` entry point
will be called as the result of an  ``open("/dev/fb0", mode)`` in the application.

Thread safety of the frame buffer driver is implementation-dependent.
The VGA driver shown below uses a mutex to prevent multiple open()
operations of the frame buffer device.

The ``frame_buffer_open()`` function returns RTEMS_SUCCESSFUL when the device driver
is successfully opened, and RTEMS_UNSATISFIED if the device is already open:
.. code:: c

    rtems_device_driver frame_buffer_close(
    rtems_device_major_number  major,
    rtems_device_minor_number  minor,
    void                      \*arg
    )
    {
    if (pthread_mutex_unlock(&mutex) == 0){
    /* restore previous state.  for VGA this means return to text mode.
    * leave out if graphics hardware has been initialized in
    * frame_buffer_initialize() \*/
    ega_hwterm();
    printk( "FBVGA close called.\\n" );
    return RTEMS_SUCCESSFUL;
    }
    return RTEMS_UNSATISFIED;
    }

In the previous example, the function ``ega_hwinit()`` takes care of
hardware-specific initialization.

Closing the Frame Buffer Device
-------------------------------

The ``frame_buffer_close()`` is invoked when the frame buffer device
is closed.  It frees up any resources allocated in``frame_buffer_open()``, and should restore previous hardware state.
The entry point corresponds to the device driver close entry point.

Returns RTEMS_SUCCESSFUL when the device driver is successfully closed:
.. code:: c

    rtems_device_driver frame_buffer_close(
    rtems_device_major_number  major,
    rtems_device_minor_number  minor,
    void                      \*arg)
    {
    pthread_mutex_unlock(&mutex);
    /* TODO check mutex return value, RTEMS_UNSATISFIED if it failed.  we
    * don't want to unconditionally call ega_hwterm()... \*/
    /* restore previous state.  for VGA this means return to text mode.
    * leave out if graphics hardware has been initialized in
    * frame_buffer_initialize() \*/
    ega_hwterm();
    printk( "frame buffer close called.\\n" );
    return RTEMS_SUCCESSFUL;
    }

Reading from the Frame Buffer Device
------------------------------------

The ``frame_buffer_read()`` is invoked from a ``read()`` operation
on the frame buffer device.
Read functions should allow normal and partial reading at the end of frame buffer memory.
This method returns RTEMS_SUCCESSFUL when the device is successfully read from:
.. code:: c

    rtems_device_driver frame_buffer_read(
    rtems_device_major_number  major,
    rtems_device_minor_number  minor,
    void                      \*arg
    )
    {
    rtems_libio_rw_args_t \*rw_args = (rtems_libio_rw_args_t \*)arg;
    rw_args->bytes_moved = ((rw_args->offset + rw_args->count) > fb_fix.smem_len ) ? (fb_fix.smem_len - rw_args->offset) : rw_args->count;
    memcpy(rw_args->buffer, (const void \*) (fb_fix.smem_start + rw_args->offset), rw_args->bytes_moved);
    return RTEMS_SUCCESSFUL;
    }

Writing to the Frame Buffer Device
----------------------------------

The ``frame_buffer_write()`` is invoked from a ``write()``
operation on the frame buffer device.
The frame buffer write function is similar to the read function, and
should handle similar cases involving partial writes.

This method returns RTEMS_SUCCESSFUL when the device is successfully
written to:
.. code:: c

    rtems_device_driver frame_buffer_write(
    rtems_device_major_number  major,
    rtems_device_minor_number  minor,
    void                      \*arg
    )
    {
    rtems_libio_rw_args_t \*rw_args = (rtems_libio_rw_args_t \*)arg;
    rw_args->bytes_moved = ((rw_args->offset + rw_args->count) > fb_fix.smem_len ) ? (fb_fix.smem_len - rw_args->offset) : rw_args->count;
    memcpy( (void \*) (fb_fix.smem_start + rw_args->offset), rw_args->buffer, rw_args->bytes_moved);
    return RTEMS_SUCCESSFUL;
    }

Frame Buffer IO Control
-----------------------

The frame buffer driver allows several ioctls, partially compatible with
the Linux kernel,
to obtain information about the hardware.

All ``ioctl()`` operations on the frame buffer device invoke``frame_buffer_control()``.

Ioctls supported:

- ioctls to get the frame buffer screen info (fixed and variable).

- ioctl to set and get palette.

.. code:: c

    rtems_device_driver frame_buffer_control(
    rtems_device_major_number  major,
    rtems_device_minor_number  minor,
    void                      \*arg
    )
    {
    rtems_libio_ioctl_args_t \*args = arg;
    printk( "FBVGA ioctl called, cmd=%x\\n", args->command  );
    switch( args->command ) {
    case FBIOGET_FSCREENINFO:
    args->ioctl_return =  get_fix_screen_info( ( struct fb_fix_screeninfo * ) args->buffer );
    break;
    case FBIOGET_VSCREENINFO:
    args->ioctl_return =  get_var_screen_info( ( struct fb_var_screeninfo * ) args->buffer );
    break;
    case FBIOPUT_VSCREENINFO:
    /* not implemented yet*/
    args->ioctl_return = -1;
    return RTEMS_UNSATISFIED;
    case FBIOGETCMAP:
    args->ioctl_return =  get_palette( ( struct fb_cmap * ) args->buffer );
    break;
    case FBIOPUTCMAP:
    args->ioctl_return =  set_palette( ( struct fb_cmap * ) args->buffer );
    break;
    default:
    args->ioctl_return = 0;
    break;
    }
    return RTEMS_SUCCESSFUL;
    }

See ``rtems/fb.h`` for more information on the list of ioctls and
data structures they work with.

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Analog Driver
#############

The Analog driver is responsible for providing an
interface to Digital to Analog Converters (DACs) and
Analog to Digital Converters (ADCs).  The capabilities provided
by this class of device driver are:

- Initialize an Analog Board

- Open a Particular Analog

- Close a Particular Analog

- Read from a Particular Analog

- Write to a Particular Analog

- Reset DACs

- Reinitialize DACS

Most analog devices are found on I/O cards that support multiple
DACs or ADCs on a single card.

There are currently no analog device drivers included in the
RTEMS source tree.  The information provided in this chapter
is based on drivers developed for applications using RTEMS.
It is hoped that this driver model information can form the
basis for a standard analog driver model that can be supported
in future RTEMS distribution.

Major and Minor Numbers
=======================

The *major* number of a device driver is its index in the
RTEMS Device Address Table.

A *minor* number is associated with each device instance
managed by a particular device driver.  An RTEMS minor number
is an ``unsigned32`` entity.  Convention calls for
dividing the bits in the minor number down into categories
like the following:

- *board* - indicates the board a particular device is located on

- *port* - indicates the particular device on a board.

From the above, it should be clear that a single device driver
can support multiple copies of the same board in a single system.
The minor number is used to distinguish the devices.

Analog Driver Configuration
===========================

There is not a standard analog driver configuration table but some
fields are common across different drivers.  The analog driver
configuration table is typically an array of structures with each
structure containing the information for a particular board.
The following is a list of the type of information normally required
to configure an analog board:

*board_offset*
    is the base address of a board.

*DAC_initial_values*
    is an array of the voltages that should be written to each DAC
    during initialization.  This allows the driver to start the board
    in a known state.

Initialize an Analog Board
==========================

At system initialization, the analog driver’s initialization entry point
will be invoked.  As part of initialization, the driver will perform
whatever board initialization is required and then set all
outputs to their configured initial state.

The analog driver may register a device name for each DAC and ADC in
the system.

Open a Particular Analog
========================

This is the driver open call.  Usually this call does nothing other than
validate the minor number.

With some drivers, it may be necessary to allocate memory when a particular
device is opened.  If that is the case, then this is often the place
to do this operation.

Close a Particular Analog
=========================

This is the driver close call.  Usually this call does nothing.

With some drivers, it may be necessary to allocate memory when a particular
device is opened.  If that is the case, then this is the place
where that memory should be deallocated.

Read from a Particular Analog
=============================

This corresponds to the driver read call.  After validating the minor
number and arguments, this call reads the indicated device.  Most analog
devices store the last value written to a DAC.  Since DACs are output
only devices, saving the last written value gives the appearance that
DACs can be read from also.  If the device is an ADC, then it is sampled.

*NOTE:* Many boards have multiple analog inputs but only one ADC.  On
these boards, it will be necessary to provide some type of mutual exclusion
during reads.  On these boards, there is a MUX which must be switched
before sampling the ADC.  After the MUX is switched, the driver must
delay some short period of time (usually microseconds) before the
signal is stable and can be sampled.  To make matters worse, some ADCs
cannot respond to wide voltage swings in a single sample.  On these
ADCs, one must do two samples when the voltage swing is too large.
On a practical basis, this means that the driver usually ends up
double sampling the ADC on these systems.

The value returned is a single precision floating point number
representing the voltage read.  This value is stored in the``argument_block`` passed in to the call.  By returning the
voltage, the caller is freed from having to know the number of
bits in the analog and board dependent conversion algorithm.

Write to a Particular Analog
============================

This corresponds to the driver write call.  After validating the minor
number and arguments, this call writes the indicated device.  If the
specified device is an ADC, then an error is usually returned.

The value written is a single precision floating point number
representing the voltage to be written to the specified DAC.
This value is stored in the ``argument_block`` passed in to the
call.  By passing the voltage to the device driver, the caller is
freed from having to know the number of bits in the analog
and board dependent conversion algorithm.

Reset DACs
==========

This is one of the IOCTL functions supported by the I/O control
device driver entry point.  When this IOCTL function is invoked,
all of the DACs are written to 0.0 volts.

Reinitialize DACS
=================

This is one of the IOCTL functions supported by the I/O control
device driver entry point.  When this IOCTL function is invoked,
all of the DACs are written with the initial value configured
for this device.

Get Last Written Values
=======================

This is one of the IOCTL functions supported by the I/O control
device driver entry point.  When this IOCTL function is invoked,
the following information is returned to the caller:

- last value written to the specified DAC

- timestamp of when the last write was performed

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Discrete Driver
###############

The Discrete driver is responsible for providing an
interface to Discrete Input/Outputs.  The capabilities provided
by this class of device driver are:

- Initialize a Discrete I/O Board

- Open a Particular Discrete Bitfield

- Close a Particular Discrete Bitfield

- Read from a Particular Discrete Bitfield

- Write to a Particular Discrete Bitfield

- Reset DACs

- Reinitialize DACS

Most discrete I/O devices are found on I/O cards that support many
bits of discrete I/O on a single card.  This driver model is centered
on the notion of reading bitfields from the card.

There are currently no discrete I/O device drivers included in the
RTEMS source tree.  The information provided in this chapter
is based on drivers developed for applications using RTEMS.
It is hoped that this driver model information can form the
discrete I/O driver model that can be supported in future RTEMS
distribution.

Major and Minor Numbers
=======================

The *major* number of a device driver is its index in the
RTEMS Device Address Table.

A *minor* number is associated with each device instance
managed by a particular device driver.  An RTEMS minor number
is an ``unsigned32`` entity.  Convention calls for
dividing the bits in the minor number down into categories
that specify a particular bitfield.  This results in categories
like the following:

- *board* - indicates the board a particular bitfield is located on

- *word* - indicates the particular word of discrete bits the
  bitfield is located within

- *start* - indicates the starting bit of the bitfield

- *width* - indicates the width of the bitfield

From the above, it should be clear that a single device driver
can support multiple copies of the same board in a single system.
The minor number is used to distinguish the devices.

By providing a way to easily access a particular bitfield from
the device driver, the application is insulated with knowing how
to mask fields in and out of a discrete I/O.

Discrete I/O Driver Configuration
=================================

There is not a standard discrete I/O driver configuration table but some
fields are common across different drivers.  The discrete I/O driver
configuration table is typically an array of structures with each
structure containing the information for a particular board.
The following is a list of the type of information normally required
to configure an discrete I/O board:

*board_offset*
    is the base address of a board.

*relay_initial_values*
    is an array of the values that should be written to each output
    word on the board during initialization.  This allows the driver
    to start with the board’s output  in a known state.

Initialize a Discrete I/O Board
===============================

At system initialization, the discrete I/O driver’s initialization entry point
will be invoked.  As part of initialization, the driver will perform
whatever board initializatin is required and then set all
outputs to their configured initial state.

The discrete I/O driver may register a device name for bitfields of
particular interest to the system.  Normally this will be restricted
to the names of each word and, if the driver supports it, an "all words".

Open a Particular Discrete Bitfield
===================================

This is the driver open call.  Usually this call does nothing other than
validate the minor number.

With some drivers, it may be necessary to allocate memory when a particular
device is opened.  If that is the case, then this is often the place
to do this operation.

Close a Particular Discrete Bitfield
====================================

This is the driver close call.  Usually this call does nothing.

With some drivers, it may be necessary to allocate memory when a particular
device is opened.  If that is the case, then this is the place
where that memory should be deallocated.

Read from a Particular Discrete Bitfield
========================================

This corresponds to the driver read call.  After validating the minor
number and arguments, this call reads the indicated bitfield.  A
discrete I/O devices may have to store the last value written to
a discrete output.  If the bitfield is output only, saving the last
written value gives the appearance that it can be read from also.
If the bitfield is input, then it is sampled.

*NOTE:* Many discrete inputs have a tendency to bounce.  The application
may have to take account for bounces.

The value returned is an ``unsigned32`` number
representing the bitfield read.  This value is stored in the``argument_block`` passed in to the call.

*NOTE:* Some discrete I/O drivers have a special minor number
used to access all discrete I/O bits on the board.  If this special
minor is used, then the area pointed to by ``argument_block`` must
be the correct size.

Write to a Particular Discrete Bitfield
=======================================

This corresponds to the driver write call.  After validating the minor
number and arguments, this call writes the indicated device.  If the
specified device is an ADC, then an error is usually returned.

The value written is an ``unsigned32`` number
representing the value to be written to the specified
bitfield.  This value is stored in the``argument_block`` passed in to the call.

*NOTE:* Some discrete I/O drivers have a special minor number
used to access all discrete I/O bits on the board.  If this special
minor is used, then the area pointed to by ``argument_block`` must
be the correct size.

Disable Discrete Outputs
========================

This is one of the IOCTL functions supported by the I/O control
device driver entry point.  When this IOCTL function is invoked,
the discrete outputs are disabled.

*NOTE:* It may not be possible to disable/enable discrete output on all
discrete I/O boards.

Enable Discrete Outputs
=======================

This is one of the IOCTL functions supported by the I/O control
device driver entry point.  When this IOCTL function is invoked,
the discrete outputs are enabled.

*NOTE:* It may not be possible to disable/enable discrete output on all
discrete I/O boards.

Reinitialize Outputs
====================

This is one of the IOCTL functions supported by the I/O control
device driver entry point.  When this IOCTL function is invoked,
the discrete outputs are rewritten with the configured initial
output values.

Get Last Written Values
=======================

This is one of the IOCTL functions supported by the I/O control
device driver entry point.  When this IOCTL function is invoked,
the following information is returned to the caller:

- last value written to the specified output word

- timestamp of when the last write was performed

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