source: rtems-docs/bsp_howto/miscellanous_support.rst @ d389819

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.