source: rtems-docs/c-user/configuring_a_system.rst @ e23f46c

.. comment SPDX-License-Identifier: CC-BY-SA-4.0

.. COMMENT: COPYRIGHT (c) 1988-2008.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.

.. _Configuring a System:

Configuring a System
********************

.. index:: configuring a system

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

RTEMS must be configured for an application.  This configuration encompasses a
variety of information including the length of each clock tick, the maximum
number of each information RTEMS object that can be created, the application
initialization tasks, the task scheduling algorithm to be used, and the device
drivers in the application.

Although this information is contained in data structures that are used by
RTEMS at system initialization time, the data structures themselves should only
rarely to be generated by hand. RTEMS provides a set of macros system which
provides a simple standard mechanism to automate the generation of these
structures.

.. index:: confdefs.h
.. index:: confdefs.h
.. index:: <rtems/confdefs.h>
.. index:: <rtems/confdefs.h>

The RTEMS header file ``<rtems/confdefs.h>`` is at the core of the automatic
generation of system configuration. It is based on the idea of setting macros
which define configuration parameters of interest to the application and
defaulting or calculating all others. This variety of macros can automatically
produce all of the configuration data required for an RTEMS application.

.. sidebar: Trivia:

  The term ``confdefs`` is shorthand for a *Configuration Defaults*.

As a general rule, application developers only specify values for the
configuration parameters of interest to them. They define what resources or
features they require. In most cases, when a parameter is not specified, it
defaults to zero (0) instances, a standards compliant value, or disabled as
appropriate. For example, by default there will be 256 task priority levels but
this can be lowered by the application. This number of priority levels is
required to be compliant with the RTEID/ORKID standards upon which the Classic
API is based. There are similar cases where the default is selected to be
compliant with with the POSIX standard.

For each configuration parameter in the configuration tables, the macro
corresponding to that field is discussed. The RTEMS Maintainers expect that all
systems can be easily configured using the ``<rtems/confdefs.h>`` mechanism and
that using this mechanism will avoid internal RTEMS configuration changes
impacting applications.

.. COMMENT: === Philosophy ===

Default Value Selection Philosophy
==================================

The user should be aware that the defaults are intentionally set as low as
possible.  By default, no application resources are configured.  The
``<rtems/confdefs.h>`` file ensures that at least one application task or
thread is configured and that at least one of the initialization task/thread
tables is configured.

.. COMMENT: === Sizing the RTEMS Workspace ===

.. _Sizing the RTEMS Workspace:

Sizing the RTEMS Workspace
==========================

The RTEMS Workspace is a user-specified block of memory reserved for use by
RTEMS.  The application should NOT modify this memory.  This area consists
primarily of the RTEMS data structures whose exact size depends upon the values
specified in the Configuration Table.  In addition, task stacks and floating
point context areas are dynamically allocated from the RTEMS Workspace.

The ``<rtems/confdefs.h>`` mechanism calculates the size of the RTEMS Workspace
automatically.  It assumes that all tasks are floating point and that all will
be allocated the minimum stack space.  This calculation includes the amount of
memory that will be allocated for internal use by RTEMS. The automatic
calculation may underestimate the workspace size truly needed by the
application, in which case one can use the ``CONFIGURE_MEMORY_OVERHEAD`` macro
to add a value to the estimate. See :ref:`Specify Memory Overhead` for more
details.

The memory area for the RTEMS Workspace is determined by the BSP.  In case the
RTEMS Workspace is too large for the available memory, then a fatal run-time
error occurs and the system terminates.

The file ``<rtems/confdefs.h>`` will calculate the value of the
``work_space_size`` parameter of the Configuration Table. There are many
parameters the application developer can specify to help ``<rtems/confdefs.h>``
in its calculations.  Correctly specifying the application requirements via
parameters such as ``CONFIGURE_EXTRA_TASK_STACKS`` and
``CONFIGURE_MAXIMUM_TASKS`` is critical for production software.

For each class of objects, the allocation can operate in one of two ways.  The
default way has an ceiling on the maximum number of object instances which can
concurrently exist in the system. Memory for all instances of that object class
is reserved at system initialization.  The second way allocates memory for an
initial number of objects and increases the current allocation by a fixed
increment when required. Both ways allocate space from inside the RTEMS
Workspace.

See :ref:`Unlimited Objects` for more details about the second way, which
allows for dynamic allocation of objects and therefore does not provide
determinism.  This mode is useful mostly for when the number of objects cannot
be determined ahead of time or when porting software for which you do not know
the object requirements.

The space needed for stacks and for RTEMS objects will vary from one version of
RTEMS and from one target processor to another.  Therefore it is safest to use
``<rtems/confdefs.h>`` and specify your application's requirements in terms of
the numbers of objects and multiples of ``RTEMS_MINIMUM_STACK_SIZE``, as far as
is possible. The automatic estimates of space required will in general change
when:

- a configuration parameter is changed,

- task or interrupt stack sizes change,

- the floating point attribute of a task changes,

- task floating point attribute is altered,

- RTEMS is upgraded, or

- the target processor is changed.

Failure to provide enough space in the RTEMS Workspace may result in fatal
run-time errors terminating the system.

.. COMMENT: === Potential Issues ===

Potential Issues with RTEMS Workspace Size Estimation
=====================================================

The ``<rtems/confdefs.h>`` file estimates the amount of memory required for the
RTEMS Workspace.  This estimate is only as accurate as the information given to
``<rtems/confdefs.h>`` and may be either too high or too low for a variety of
reasons.  Some of the reasons that ``<rtems/confdefs.h>`` may reserve too much
memory for RTEMS are:

- All tasks/threads are assumed to be floating point.

Conversely, there are many more reasons that the resource estimate could be too
low:

- Task/thread stacks greater than minimum size must be accounted for explicitly
  by developer.

- Memory for messages is not included.

- Device driver requirements are not included.

- Network stack requirements are not included.

- Requirements for add-on libraries are not included.

In general, ``<rtems/confdefs.h>`` is very accurate when given enough
information.  However, it is quite easy to use a library and forget to account
for its resources.

.. COMMENT: === Format to be followed for making changes in this file ===

Format to be followed for making changes in this file
=====================================================

MACRO NAME:
  Should be alphanumeric. Can have '_' (underscore).

DATA TYPE:
  Please refer to all existing formats.

RANGE:
  The range depends on the Data Type of the macro.

  - If the data type is of type task priority, then its value should be an
    integer in the range of 1 to 255.

  - If the data type is an integer, then it can have numbers, characters (in
    case the value is defined using another macro) and arithmetic operations
    (+, -, \*, /).

  - If the data type is a function pointer the first character should be an
    alphabet or an underscore. The rest of the string can be alphanumeric.

  - If the data type is RTEMS Attributes or RTEMS Mode then the string should
    be alphanumeric.

  - If the data type is RTEMS NAME then the value should be an integer>=0 or
    ``RTEMS_BUILD_NAME( 'U', 'I', '1', ' ' )``

DEFAULT VALUE:
  The default value should be in the following formats- Please note that the
  '.' (full stop) is necessary.

  - In case the value is not defined then: This is not defined by default.

  - If we know the default value then: The default value is XXX.

  - If the default value is BSP Specific then: This option is BSP specific.

DESCRIPTION:
  The description of the macro. (No specific format)

NOTES:
  Any further notes. (No specific format)

.. COMMENT: === Configuration Example ===

Configuration Example
=====================

In the following example, the configuration information for a system with a
single message queue, four (4) tasks, and a timeslice of fifty (50)
milliseconds is as follows:

.. code-block:: c

    #include <bsp.h>
    #define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER
    #define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER
    #define CONFIGURE_MICROSECONDS_PER_TICK   1000 /* 1 millisecond */
    #define CONFIGURE_TICKS_PER_TIMESLICE       50 /* 50 milliseconds */
    #define CONFIGURE_RTEMS_INIT_TASKS_TABLE
    #define CONFIGURE_MAXIMUM_TASKS 4
    #define CONFIGURE_MAXIMUM_MESSAGE_QUEUES 1
    #define CONFIGURE_MESSAGE_BUFFER_MEMORY \
               CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE(20, sizeof(struct USER_MESSAGE))
    #define CONFIGURE_INIT
    #include <rtems/confdefs.h>

In this example, only a few configuration parameters are specified. The impact
of these are as follows:

- The example specified ``CONFIGURE_RTEMS_INIT_TASK_TABLE`` but did not specify
  any additional parameters. This results in a configuration of an application
  which will begin execution of a single initialization task named ``Init``
  which is non-preemptible and at priority one (1).

- By specifying ``CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER``, this application
  is configured to have a clock tick device driver. Without a clock tick device
  driver, RTEMS has no way to know that time is passing and will be unable to
  support delays and wall time. Further configuration details about time are
  provided. Per ``CONFIGURE_MICROSECONDS_PER_TICK`` and
  ``CONFIGURE_TICKS_PER_TIMESLICE``, the user specified they wanted a clock
  tick to occur each millisecond, and that the length of a timeslice would be
  fifty (50) milliseconds.

- By specifying ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER``, the application
  will include a console device driver. Although the console device driver may
  support a combination of multiple serial ports and display and keyboard
  combinations, it is only required to provide a single device named
  ``/dev/console``. This device will be used for Standard Input, Output and
  Error I/O Streams. Thus when ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER``
  is specified, implicitly three (3) file descriptors are reserved for the
  Standard I/O Streams and those file descriptors are associated with
  ``/dev/console`` during initialization. All console devices are expected to
  support the POSIX*termios* interface.

- The example above specifies via ``CONFIGURE_MAXIMUM_TASKS`` that the
  application requires a maximum of four (4) simultaneously existing Classic
  API tasks. Similarly, by specifying ``CONFIGURE_MAXIMUM_MESSAGE_QUEUES``,
  there may be a maximum of only one (1) concurrently existent Classic API
  message queues.

- The most surprising configuration parameter in this example is the use of
  ``CONFIGURE_MESSAGE_BUFFER_MEMORY``. Message buffer memory is allocated from
  the RTEMS Workspace and must be accounted for. In this example, the single
  message queue will have up to twenty (20) messages of type ``struct
  USER_MESSAGE``.

- The ``CONFIGURE_INIT`` constant must be defined in order to make
  ``<rtems/confdefs.h>`` instantiate the configuration data structures.  This
  can only be defined in one source file per application that includes
  ``<rtems/confdefs.h>`` or the symbol table will be instantiated multiple
  times and linking errors produced.

This example illustrates that parameters have default values. Among other
things, the application implicitly used the following defaults:

- All unspecified types of communications and synchronization objects in the
  Classic and POSIX Threads API have maximums of zero (0).

- The filesystem will be the default filesystem which is the In-Memory File
  System (IMFS).

- The application will have the default number of priority levels.

- The minimum task stack size will be that recommended by RTEMS for the target
  architecture.

.. COMMENT: === Unlimited Objects ===

.. _Unlimited Objects:

Unlimited Objects
=================

In real-time embedded systems the RAM is normally a limited, critical resource
and dynamic allocation is avoided as much as possible to ensure predictable,
deterministic execution times. For such cases, see :ref:`Sizing the RTEMS
Workspace` for an overview of how to tune the size of the workspace.
Frequently when users are porting software to RTEMS the precise resource
requirements of the software is unknown. In these situations users do not need
to control the size of the workspace very tightly because they just want to get
the new software to run; later they can tune the workspace size as needed.

The following API-independent object classes can be configured in unlimited
mode:

- POSIX Keys

- POSIX Key Value Pairs

The following object classes in the Classic API can be configured in unlimited
mode:

- Tasks

- Timers

- Semaphores

- Message Queues

- Periods

- Barriers

- Partitions

- Regions

- Ports

Additionally, the following object classes from the POSIX API can be configured
in unlimited mode:

- Threads

- Mutexes

- Condition Variables

- Timers

- Message Queues

- Message Queue Descriptors

- Semaphores

- Barriers

- Read/Write Locks

- Spinlocks

The following object classes can *not* be configured in unlimited mode:

- Drivers

- File Descriptors

- User Extensions

- POSIX Queued Signals

Due to the memory requirements of unlimited objects it is strongly recommended
to use them only in combination with the unified work areas. See :ref:`Separate
or Unified Work Areas` for more information on unified work areas.

The following example demonstrates how the two simple configuration defines for
unlimited objects and unified works areas can replace many seperate
configuration defines for supported object classes:

.. code-block:: c

    #define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER
    #define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER
    #define CONFIGURE_UNIFIED_WORK_AREAS
    #define CONFIGURE_UNLIMITED_OBJECTS
    #define CONFIGURE_RTEMS_INIT_TASKS_TABLE
    #define CONFIGURE_INIT
    #include <rtems/confdefs.h>

Users are cautioned that using unlimited objects is not recommended for
production software unless the dynamic growth is absolutely required. It is
generally considered a safer embedded systems programming practice to know the
system limits rather than experience an out of memory error at an arbitrary and
largely unpredictable time in the field.

.. COMMENT: === Per Object Class Unlimited Object Instances ===

.. _Per Object Class Unlimited Object Instances:

Per Object Class Unlimited Object Instances
-------------------------------------------
.. index:: rtems_resource_unlimited

When the number of objects is not known ahead of time, RTEMS provides an
auto-extending mode that can be enabled individually for each object type by
using the macro ``rtems_resource_unlimited``. This takes a value as a
parameter, and is used to set the object maximum number field in an API
Configuration table. The value is an allocation unit size. When RTEMS is
required to grow the object table it is grown by this size. The kernel will
return the object memory back to the RTEMS Workspace when an object is
destroyed. The kernel will only return an allocated block of objects to the
RTEMS Workspace if at least half the allocation size of free objects remain
allocated. RTEMS always keeps one allocation block of objects allocated. Here
is an example of using ``rtems_resource_unlimited``:

.. code-block:: c

    #define CONFIGURE_MAXIMUM_TASKS rtems_resource_unlimited(5)

.. index:: rtems_resource_is_unlimited
.. index:: rtems_resource_maximum_per_allocation

Object maximum specifications can be evaluated with the
``rtems_resource_is_unlimited`` and``rtems_resource_maximum_per_allocation``
macros.

.. COMMENT: === Unlimited Object Instances ===

.. _Unlimited Object Instances:

Unlimited Object Instances
--------------------------

To ease the burden of developers who are porting new software RTEMS also
provides the capability to make all object classes listed above operate in
unlimited mode in a simple manner. The application developer is only
responsible for enabling unlimited objects and specifying the allocation size.

.. COMMENT: === CONFIGURE_UNLIMITED_OBJECTS ===

.. _Enable Unlimited Object Instances:

Enable Unlimited Object Instances
---------------------------------
.. index:: CONFIGURE_UNLIMITED_OBJECTS

CONSTANT:
    ``CONFIGURE_UNLIMITED_OBJECTS``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_UNLIMITED_OBJECTS`` enables ``rtems_resource_unlimited`` mode
    for Classic API and POSIX API objects that do not already have a specific
    maximum limit defined.

NOTES:
    When using unlimited objects, it is common practice to also specify
    ``CONFIGURE_UNIFIED_WORK_AREAS`` so the system operates with a single pool
    of memory for both RTEMS and application memory allocations.

.. COMMENT: === CONFIGURE_UNLIMITED_ALLOCATION_SIZE ===

.. _Specify Unlimited Objects Allocation Size:

Specify Unlimited Objects Allocation Size
-----------------------------------------

CONSTANT:
    ``CONFIGURE_UNLIMITED_ALLOCATION_SIZE``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    If not defined and ``CONFIGURE_UNLIMITED_OBJECTS`` is defined, the default
    value is eight (8).

DESCRIPTION:
    ``CONFIGURE_UNLIMITED_ALLOCATION_SIZE`` provides an allocation size to use
    for ``rtems_resource_unlimited`` when using
    ``CONFIGURE_UNLIMITED_OBJECTS``.

NOTES:
    By allowing users to declare all resources as being unlimited the user can
    avoid identifying and limiting the resources
    used. ``CONFIGURE_UNLIMITED_OBJECTS`` does not support varying the
    allocation sizes for different objects; users who want that much control
    can define the ``rtems_resource_unlimited`` macros themselves.

.. code-block:: c

    #define CONFIGURE_UNLIMITED_OBJECTS
    #define CONFIGURE_UNLIMITED_ALLOCATION_SIZE 5

.. COMMENT: === Classic API Configuration ===

Classic API Configuration
=========================

This section defines the Classic API related system configuration parameters
supported by ``<rtems/confdefs.h>``.

.. COMMENT: === CONFIGURE_MAXIMUM_TASKS ===

.. _Specify Maximum Classic API Tasks:

Specify Maximum Classic API Tasks
---------------------------------
.. index:: CONFIGURE_MAXIMUM_TASKS

CONSTANT:
    ``CONFIGURE_MAXIMUM_TASKS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is ``0``.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_TASKS`` is the maximum number of Classic API Tasks that
    can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

    The calculations for the required memory in the RTEMS Workspace for tasks
    assume that each task has a minimum stack size and has floating point
    support enabled.  The configuration parameter
    ``CONFIGURE_EXTRA_TASK_STACKS`` is used to specify task stack requirements
    *ABOVE* the minimum size required.  See :ref:`Reserve Task/Thread Stack
    Memory Above Minimum` for more information about
    ``CONFIGURE_EXTRA_TASK_STACKS``.

    The maximum number of POSIX threads is specified by
    ``CONFIGURE_MAXIMUM_POSIX_THREADS``.

    A future enhancement to ``<rtems/confdefs.h>`` could be to eliminate the
    assumption that all tasks have floating point enabled. This would require
    the addition of a new configuration parameter to specify the number of
    tasks which enable floating point support.

.. COMMENT: XXX - Add xref to CONFIGURE_MAXIMUM_POSIX_THREADS.

.. COMMENT: === CONFIGURE_ENABLE_CLASSIC_API_NOTEPADS ===

.. _Specify Maximum Classic API Timers:

Specify Maximum Classic API Timers
----------------------------------
.. index:: CONFIGURE_ENABLE_CLASSIC_API_NOTEPADS

CONSTANT:
    ``CONFIGURE_ENABLE_CLASSIC_API_NOTEPADS``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default, and Classic API Notepads are not supported.

DESCRIPTION:
    ``CONFIGURE_ENABLE_CLASSIC_API_NOTEPADS`` should be defined if the
    user wants to have support for Classic API Notepads in their application.

NOTES:
    Disabling Classic API Notepads saves the allocation of sixteen (16)
    thirty-two bit integers. This saves sixty-four bytes per task/thread
    plus the allocation overhead. Notepads are rarely used in applications
    and this can save significant memory in a low RAM system. Classic API
    Notepads are deprecated, and this option has been removed from
    post 4.11 versions of RTEMS.

.. COMMENT: === CONFIGURE_MAXIMUM_TIMERS ===

.. _Specify Maximum Classic API Timers:

Specify Maximum Classic API Timers
----------------------------------
.. index:: CONFIGURE_MAXIMUM_TIMERS

CONSTANT:
    ``CONFIGURE_MAXIMUM_TIMERS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_TIMERS`` is the maximum number of Classic API Timers
    that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_SEMAPHORES ===

.. _Specify Maximum Classic API Semaphores:

Specify Maximum Classic API Semaphores
--------------------------------------
.. index:: CONFIGURE_MAXIMUM_SEMAPHORES

CONSTANT:
    ``CONFIGURE_MAXIMUM_SEMAPHORES``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_SEMAPHORES`` is the maximum number of Classic API
    Semaphores that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_MRSP_SEMAPHORES ===

.. _Specify Maximum Classic API Semaphores usable with MrsP:

Specify Maximum Classic API Semaphores usable with MrsP
-------------------------------------------------------
.. index:: CONFIGURE_MAXIMUM_MRSP_SEMAPHORES

CONSTANT:
    ``CONFIGURE_MAXIMUM_MRSP_SEMAPHORES``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_MRSP_SEMAPHORES`` is the maximum number of Classic API
    Semaphores using the Multiprocessor Resource Sharing Protocol (MrsP) that
    can be concurrently active.

NOTES:
    This configuration option is only used on SMP configurations.  On
    uni-processor configurations the Priority Ceiling Protocol is used for MrsP
    semaphores and thus no extra memory is necessary.

.. COMMENT: === CONFIGURE_MAXIMUM_MESSAGE_QUEUES ===

.. _Specify Maximum Classic API Message Queues:

Specify Maximum Classic API Message Queues
------------------------------------------
.. index:: CONFIGURE_MAXIMUM_MESSAGE_QUEUES

CONSTANT:
    ``CONFIGURE_MAXIMUM_MESSAGE_QUEUES``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_MESSAGE_QUEUES`` is the maximum number of Classic API
    Message Queues that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_BARRIERS ===

.. _Specify Maximum Classic API Barriers:

Specify Maximum Classic API Barriers
------------------------------------
.. index:: CONFIGURE_MAXIMUM_BARRIERS

CONSTANT:
    ``CONFIGURE_MAXIMUM_BARRIERS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_BARRIERS`` is the maximum number of Classic API
    Barriers that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_PERIODS ===

.. _Specify Maximum Classic API Periods:

Specify Maximum Classic API Periods
-----------------------------------
.. index:: CONFIGURE_MAXIMUM_PERIODS

CONSTANT:
    ``CONFIGURE_MAXIMUM_PERIODS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_PERIODS`` is the maximum number of Classic API Periods
    that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_PARTITIONS ===

.. _Specify Maximum Classic API Partitions:

Specify Maximum Classic API Partitions
--------------------------------------
.. index:: CONFIGURE_MAXIMUM_PARTITIONS

CONSTANT:
    ``CONFIGURE_MAXIMUM_PARTITIONS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_PARTITIONS`` is the maximum number of Classic API
    Partitions that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_REGIONS ===

.. _Specify Maximum Classic API Regions:

Specify Maximum Classic API Regions
-----------------------------------
.. index:: CONFIGURE_MAXIMUM_REGIONS

CONSTANT:
    ``CONFIGURE_MAXIMUM_REGIONS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_REGIONS`` is the maximum number of Classic API Regions
    that can be concurrently active.

NOTES:
    None.

.. COMMENT: === CONFIGURE_MAXIMUM_PORTS ===

.. _Specify Maximum Classic API Ports:

Specify Maximum Classic API Ports
---------------------------------
.. index:: CONFIGURE_MAXIMUM_PORTS

CONSTANT:
    ``CONFIGURE_MAXIMUM_PORTS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_PORTS`` is the maximum number of Classic API Ports that
    can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_USER_EXTENSIONS ===

.. _Specify Maximum Classic API User Extensions:

Specify Maximum Classic API User Extensions
-------------------------------------------
.. index:: CONFIGURE_MAXIMUM_USER_EXTENSIONS

CONSTANT:
    ``CONFIGURE_MAXIMUM_USER_EXTENSIONS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_USER_EXTENSIONS`` is the maximum number of Classic API
    User Extensions that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === Classic API Initialization Task Configuration ===

Classic API Initialization Tasks Table Configuration
====================================================

The ``<rtems/confdefs.h>`` configuration system can automatically generate an
Initialization Tasks Table named ``Initialization_tasks`` with a single entry.
The following parameters control the generation of that table.

.. COMMENT: === CONFIGURE_RTEMS_INIT_TASKS_TABLE ===

.. _Instantiate Classic API Initialization Task Table:

Instantiate Classic API Initialization Task Table
-------------------------------------------------
.. index:: CONFIGURE_RTEMS_INIT_TASKS_TABLE

CONSTANT:
    ``CONFIGURE_RTEMS_INIT_TASKS_TABLE``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_RTEMS_INIT_TASKS_TABLE`` is defined if the user wishes to use a
    Classic RTEMS API Initialization Task Table. The table built by
    ``<rtems/confdefs.h>`` specifies the parameters for a single task. This is
    sufficient for applications which initialization the system from a single
    task.

    By default, this field is not defined as the user MUST select their own API
    for initialization tasks.

NOTES:
    The application may choose to use the initialization tasks or threads table
    from another API.

    A compile time error will be generated if the user does not configure any
    initialization tasks or threads.

.. COMMENT: === CONFIGURE_INIT_TASK_ENTRY_POINT ===

.. _Specifying Classic API Initialization Task Entry Point:

Specifying Classic API Initialization Task Entry Point
------------------------------------------------------
.. index:: CONFIGURE_INIT_TASK_ENTRY_POINT

CONSTANT:
    ``CONFIGURE_INIT_TASK_ENTRY_POINT``

DATA TYPE:
    Task entry function pointer (``rtems_task_entry``).

RANGE:
    Valid task entry function pointer.

DEFAULT VALUE:
    The default value is ``Init``.

DESCRIPTION:
    ``CONFIGURE_INIT_TASK_ENTRY_POINT`` is the entry point (a.k.a. function
    name) of the single initialization task defined by the Classic API
    Initialization Tasks Table.

NOTES:
    The user must implement the function ``Init`` or the function name provided
    in this configuration parameter.

.. COMMENT: === CONFIGURE_INIT_TASK_NAME ===

.. _Specifying Classic API Initialization Task Name:

Specifying Classic API Initialization Task Name
-----------------------------------------------
.. index:: CONFIGURE_INIT_TASK_NAME

CONSTANT:
    ``CONFIGURE_INIT_TASK_NAME``

DATA TYPE:
    RTEMS Name (``rtems_name``).

RANGE:
    Any value.

DEFAULT VALUE:
    The default value is ``rtems_build_name( 'U', 'I', '1', ' ' )``.

DESCRIPTION:
    ``CONFIGURE_INIT_TASK_NAME`` is the name of the single initialization task
    defined by the Classic API Initialization Tasks Table.

NOTES:
    None.

.. COMMENT: === CONFIGURE_INIT_TASK_STACK_SIZE ===

.. _Specifying Classic API Initialization Task Stack Size:

Specifying Classic API Initialization Task Stack Size
-----------------------------------------------------
.. index:: CONFIGURE_INIT_TASK_STACK_SIZE

CONSTANT:
    ``CONFIGURE_INIT_TASK_STACK_SIZE``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is RTEMS_MINIMUM_STACK_SIZE.

DESCRIPTION:
    ``CONFIGURE_INIT_TASK_STACK_SIZE`` is the stack size of the single
    initialization task defined by the Classic API Initialization Tasks Table.

NOTES:
    If the stack size specified is greater than the configured minimum, it must
    be accounted for in ``CONFIGURE_EXTRA_TASK_STACKS``.  See :ref:`Reserve
    Task/Thread Stack Memory Above Minimum` for more information about
    ``CONFIGURE_EXTRA_TASK_STACKS``.

.. COMMENT: === CONFIGURE_INIT_TASK_PRIORITY ===

.. _Specifying Classic API Initialization Task Priority:

Specifying Classic API Initialization Task Priority
---------------------------------------------------
.. index:: CONFIGURE_INIT_TASK_PRIORITY

CONSTANT:
    ``CONFIGURE_INIT_TASK_PRIORITY``

DATA TYPE:
    RTEMS Task Priority (``rtems_task_priority``).

RANGE:
    One (1) to CONFIGURE_MAXIMUM_PRIORITY.

DEFAULT VALUE:
    The default value is 1, which is the highest priority in the Classic API.

DESCRIPTION:
    ``CONFIGURE_INIT_TASK_PRIORITY`` is the initial priority of the single
    initialization task defined by the Classic API Initialization Tasks Table.

NOTES:
    None.

.. COMMENT: === CONFIGURE_INIT_TASK_ATTRIBUTES ===

.. _Specifying Classic API Initialization Task Attributes:

Specifying Classic API Initialization Task Attributes
-----------------------------------------------------
.. index:: CONFIGURE_INIT_TASK_ATTRIBUTES

CONSTANT:
    ``CONFIGURE_INIT_TASK_ATTRIBUTES``

DATA TYPE:
    RTEMS Attributes (``rtems_attribute``).

RANGE:
    Valid task attribute sets.

DEFAULT VALUE:
    The default value is ``RTEMS_DEFAULT_ATTRIBUTES``.

DESCRIPTION:
    ``CONFIGURE_INIT_TASK_ATTRIBUTES`` is the task attributes of the single
    initialization task defined by the Classic API Initialization Tasks Table.

NOTES:
    None.

.. COMMENT: === CONFIGURE_INIT_TASK_INITIAL_MODES ===

.. _Specifying Classic API Initialization Task Modes:

Specifying Classic API Initialization Task Modes
------------------------------------------------
.. index:: CONFIGURE_INIT_TASK_INITIAL_MODES

CONSTANT:
    ``CONFIGURE_INIT_TASK_INITIAL_MODES``

DATA TYPE:
    RTEMS Mode (``rtems_mode``).

RANGE:
    Valid task mode sets.

DEFAULT VALUE:
    The default value is ``RTEMS_NO_PREEMPT``.

DESCRIPTION:
    ``CONFIGURE_INIT_TASK_INITIAL_MODES`` is the initial execution mode of the
    single initialization task defined by the Classic API Initialization Tasks
    Table.

NOTES:
    None.

.. COMMENT: === CONFIGURE_INIT_TASK_ARGUMENTS ===

.. _Specifying Classic API Initialization Task Arguments:

Specifying Classic API Initialization Task Arguments
----------------------------------------------------
.. index:: CONFIGURE_INIT_TASK_ARGUMENTS

CONSTANT:
    ``CONFIGURE_INIT_TASK_ARGUMENTS``

DATA TYPE:
    RTEMS Task Argument (``rtems_task_argument``).

RANGE:
    Complete range of the type.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_INIT_TASK_ARGUMENTS`` is the task argument of the single
    initialization task defined by the Classic API Initialization Tasks Table.

NOTES:
    None.

.. COMMENT: === CONFIGURE_HAS_OWN_INIT_TASK_TABLE ===

.. _Not Using Generated Initialization Tasks Table:

Not Using Generated Initialization Tasks Table
----------------------------------------------
.. index:: CONFIGURE_HAS_OWN_INIT_TASK_TABLE

CONSTANT:
    ``CONFIGURE_HAS_OWN_INIT_TASK_TABLE``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_HAS_OWN_INIT_TASK_TABLE`` is defined if the user wishes to
    define their own Classic API Initialization Tasks Table.  This table should
    be named ``Initialization_tasks``.

NOTES:
    This is a seldom used configuration parameter. The most likely use case is
    when an application desires to have more than one initialization task.

.. COMMENT: === POSIX API Configuration ===

POSIX API Configuration
=======================

The parameters in this section are used to configure resources for the RTEMS
POSIX API.  They are only relevant if the POSIX API is enabled at configure
time using the ``--enable-posix`` option.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_THREADS ===

.. _Specify Maximum POSIX API Threads:

Specify Maximum POSIX API Threads
---------------------------------
.. index:: CONFIGURE_MAXIMUM_POSIX_THREADS

CONSTANT:
    ``CONFIGURE_MAXIMUM_POSIX_THREADS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_POSIX_THREADS`` is the maximum number of POSIX API
    Threads that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

    This calculations for the required memory in the RTEMS Workspace for
    threads assume that each thread has a minimum stack size and has floating
    point support enabled.  The configuration parameter
    ``CONFIGURE_EXTRA_TASK_STACKS`` is used to specify thread stack
    requirements *ABOVE* the minimum size required.  See :ref:`Reserve
    Task/Thread Stack Memory Above Minimum` for more information about
    ``CONFIGURE_EXTRA_TASK_STACKS``.

    The maximum number of Classic API Tasks is specified by
    ``CONFIGURE_MAXIMUM_TASKS``.

    All POSIX threads have floating point enabled.

.. COMMENT: XXX - Add xref to CONFIGURE_MAXIMUM_TASKS.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_MUTEXES ===

.. _Specify Maximum POSIX API Mutexes:

Specify Maximum POSIX API Mutexes
---------------------------------
.. index:: CONFIGURE_MAXIMUM_POSIX_MUTEXES

CONSTANT:
    ``CONFIGURE_MAXIMUM_POSIX_MUTEXES``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_POSIX_MUTEXES`` is the maximum number of POSIX API
    Mutexes that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES ===

.. _Specify Maximum POSIX API Condition Variables:

Specify Maximum POSIX API Condition Variables
---------------------------------------------
.. index:: CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES

CONSTANT:
    ``CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES`` is the maximum number of
    POSIX API Condition Variables that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_KEYS ===

.. _Specify Maximum POSIX API Keys:

Specify Maximum POSIX API Keys
------------------------------
.. index:: CONFIGURE_MAXIMUM_POSIX_KEYS

CONSTANT:
    ``CONFIGURE_MAXIMUM_POSIX_KEYS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_POSIX_KEYS`` is the maximum number of POSIX API Keys
    that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: XXX - Key pairs

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_TIMERS ===

.. _Specify Maximum POSIX API Timers:

Specify Maximum POSIX API Timers
--------------------------------
.. index:: CONFIGURE_MAXIMUM_POSIX_TIMERS

CONSTANT:
    ``CONFIGURE_MAXIMUM_POSIX_TIMERS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_POSIX_TIMERS`` is the maximum number of POSIX API
    Timers that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS ===

.. _Specify Maximum POSIX API Queued Signals:

Specify Maximum POSIX API Queued Signals
----------------------------------------
.. index:: CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS

CONSTANT:
    ``CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS`` is the maximum number of POSIX
    API Queued Signals that can be concurrently active.

NOTES:
    None.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES ===

.. _Specify Maximum POSIX API Message Queues:

Specify Maximum POSIX API Message Queues
----------------------------------------
.. index:: CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES

CONSTANT:
    ``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES`` is the maximum number of POSIX
    API Message Queues that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_SEMAPHORES ===

.. _Specify Maximum POSIX API Semaphores:

Specify Maximum POSIX API Semaphores
------------------------------------
.. index:: CONFIGURE_MAXIMUM_POSIX_SEMAPHORES

CONSTANT:
    ``CONFIGURE_MAXIMUM_POSIX_SEMAPHORES``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_POSIX_SEMAPHORES`` is the maximum number of POSIX API
    Semaphores that can be concurrently active.

NOTES:
    None.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_BARRIERS ===

.. _Specify Maximum POSIX API Barriers:

Specify Maximum POSIX API Barriers
----------------------------------
.. index:: CONFIGURE_MAXIMUM_POSIX_BARRIERS

CONSTANT:
    ``CONFIGURE_MAXIMUM_POSIX_BARRIERS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_POSIX_BARRIERS`` is the maximum number of POSIX API
    Barriers that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_SPINLOCKS ===

.. _Specify Maximum POSIX API Spinlocks:

Specify Maximum POSIX API Spinlocks
-----------------------------------
.. index:: CONFIGURE_MAXIMUM_POSIX_SPINLOCKS

CONSTANT:
    ``CONFIGURE_MAXIMUM_POSIX_SPINLOCKS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_POSIX_SPINLOCKS`` is the maximum number of POSIX API
    Spinlocks that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_RWLOCKS ===

.. _Specify Maximum POSIX API Read/Write Locks:

Specify Maximum POSIX API Read/Write Locks
------------------------------------------
.. index:: CONFIGURE_MAXIMUM_POSIX_RWLOCKS

CONSTANT:
    ``CONFIGURE_MAXIMUM_POSIX_RWLOCKS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_POSIX_RWLOCKS`` is the maximum number of POSIX API
    Read/Write Locks that can be concurrently active.

NOTES:
    This object class can be configured in unlimited allocation mode.

.. COMMENT: === POSIX Initialization Threads Table Configuration ===

POSIX Initialization Threads Table Configuration
================================================

The ``<rtems/confdefs.h>`` configuration system can automatically generate a
POSIX Initialization Threads Table named ``POSIX_Initialization_threads`` with
a single entry.  The following parameters control the generation of that table.

.. COMMENT: === CONFIGURE_POSIX_INIT_THREAD_TABLE ===

.. _Instantiate POSIX API Initialization Thread Table:

Instantiate POSIX API Initialization Thread Table
-------------------------------------------------
.. index:: CONFIGURE_POSIX_INIT_THREAD_TABLE

CONSTANT:

    ``CONFIGURE_POSIX_INIT_THREAD_TABLE``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This field is not defined by default, as the user MUST select their own API
    for initialization tasks.

DESCRIPTION:
    ``CONFIGURE_POSIX_INIT_THREAD_TABLE`` is defined if the user wishes to use
    a POSIX API Initialization Threads Table.  The table built by
    ``<rtems/confdefs.h>`` specifies the parameters for a single thread. This
    is sufficient for applications which initialization the system from a
    single task.

    By default, this field is not defined as the user MUST select their own API
    for initialization tasks.

NOTES:
    The application may choose to use the initialization tasks or threads table
    from another API.

    A compile time error will be generated if the user does not configure any
    initialization tasks or threads.

.. COMMENT: === CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT ===

.. _Specifying POSIX API Initialization Thread Entry Point:

Specifying POSIX API Initialization Thread Entry Point
------------------------------------------------------
.. index:: CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT

CONSTANT:
    ``CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT``

DATA TYPE:
    POSIX thread function pointer (``void *(*entry_point)(void *)``).

RANGE:
    Undefined or a valid POSIX thread function pointer.

DEFAULT VALUE:
    The default value is ``POSIX_Init``.

DESCRIPTION:
    ``CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT`` is the entry point
    (a.k.a. function name) of the single initialization thread defined by the
    POSIX API Initialization Threads Table.

NOTES:
    The user must implement the function ``POSIX_Init`` or the function name
    provided in this configuration parameter.

.. COMMENT: === CONFIGURE_POSIX_INIT_THREAD_STACK_SIZE ===

.. _Specifying POSIX API Initialization Thread Stack Size:

Specifying POSIX API Initialization Thread Stack Size
-----------------------------------------------------
.. index:: CONFIGURE_POSIX_INIT_THREAD_STACK_SIZE

CONSTANT:
    ``CONFIGURE_POSIX_INIT_THREAD_STACK_SIZE``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 2 \* RTEMS_MINIMUM_STACK_SIZE.

DESCRIPTION:
    ``CONFIGURE_POSIX_INIT_THREAD_STACK_SIZE`` is the stack size of the single
    initialization thread defined by the POSIX API Initialization Threads
    Table.

NOTES:
    If the stack size specified is greater than the configured minimum, it must
    be accounted for in ``CONFIGURE_EXTRA_TASK_STACKS``.  See :ref:`Reserve
    Task/Thread Stack Memory Above Minimum` for more information about
    ``CONFIGURE_EXTRA_TASK_STACKS``.

.. COMMENT: === CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE ===

.. _Not Using Generated POSIX Initialization Threads Table:

Not Using Generated POSIX Initialization Threads Table
------------------------------------------------------
.. index:: CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE

CONSTANT:
    ``CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE`` is defined if the user wishes
    to define their own POSIX API Initialization Threads Table.  This table
    should be named ``POSIX_Initialization_threads``.

NOTES:
    This is a seldom used configuration parameter. The most likely use case is
    when an application desires to have more than one initialization task.

.. COMMENT: === Basic System Information ===

Basic System Information
========================

This section defines the general system configuration parameters supported by
``<rtems/confdefs.h>``.

.. COMMENT: === CONFIGURE_UNIFIED_WORK_AREAS ===

.. _Separate or Unified Work Areas:

Separate or Unified Work Areas
------------------------------
.. index:: CONFIGURE_UNIFIED_WORK_AREAS
.. index:: unified work areas
.. index:: separate work areas
.. index:: RTEMS Workspace
.. index:: C Program Heap

CONSTANT:
    ``CONFIGURE_UNIFIED_WORK_AREAS``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default, which specifies that the C Program Heap and
    the RTEMS Workspace will be separate.

DESCRIPTION:
    When defined, the C Program Heap and the RTEMS Workspace will be one pool
    of memory.

    When not defined, there will be separate memory pools for the RTEMS
    Workspace and C Program Heap.

NOTES:
    Having separate pools does have some advantages in the event a task blows a
    stack or writes outside its memory area. However, in low memory systems the
    overhead of the two pools plus the potential for unused memory in either
    pool is very undesirable.

    In high memory environments, this is desirable when you want to use the
    RTEMS "unlimited" objects option.  You will be able to create objects until
    you run out of all available memory rather then just until you run out of
    RTEMS Workspace.

.. COMMENT: === CONFIGURE_MICROSECONDS_PER_TICK ===

.. _CONFIGURE_MICROSECONDS_PER_TICK:

Length of Each Clock Tick
-------------------------
.. index:: CONFIGURE_MICROSECONDS_PER_TICK
.. index:: tick quantum

CONSTANT:
    ``CONFIGURE_MICROSECONDS_PER_TICK``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    This is not defined by default. When not defined, the clock tick quantum is
    configured to be 10,000 microseconds which is ten (10) milliseconds.

DESCRIPTION:
    This constant is  used to specify the length of time between clock ticks.

    When the clock tick quantum value is too low, the system will spend so much
    time processing clock ticks that it does not have processing time available
    to perform application work. In this case, the system will become
    unresponsive.

    The lowest practical time quantum varies widely based upon the speed of the
    target hardware and the architectural overhead associated with
    interrupts. In general terms, you do not want to configure it lower than is
    needed for the application.

    The clock tick quantum should be selected such that it all blocking and
    delay times in the application are evenly divisible by it. Otherwise,
    rounding errors will be introduced which may negatively impact the
    application.

NOTES:
    This configuration parameter has no impact if the Clock Tick Device driver
    is not configured.

    There may be BSP specific limits on the resolution or maximum value of a
    clock tick quantum.

.. COMMENT: === CONFIGURE_TICKS_PER_TIMESLICE ===

.. _Specifying Timeslicing Quantum:

Specifying Timeslicing Quantum
------------------------------
.. index:: CONFIGURE_TICKS_PER_TIMESLICE
.. index:: ticks per timeslice

CONSTANT:
    ``CONFIGURE_TICKS_PER_TIMESLICE``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is 50.

DESCRIPTION:
    This configuration parameter specifies the length of the timeslice quantum
    in ticks for each task.

NOTES:
    This configuration parameter has no impact if the Clock Tick Device driver
    is not configured.

.. COMMENT: === CONFIGURE_MAXIMUM_PRIORITY ===

.. _Specifying the Number of Thread Priority Levels:

Specifying the Number of Thread Priority Levels
-----------------------------------------------
.. index:: CONFIGURE_MAXIMUM_PRIORITY
.. index:: maximum priority
.. index:: number of priority levels

CONSTANT:
    ``CONFIGURE_MAXIMUM_PRIORITY``

DATA TYPE:
    Unsigned integer (``uint8_t``).

RANGE:
    Valid values for this configuration parameter must be one (1) less than
    than a power of two (2) between 4 and 256 inclusively.  In other words,
    valid values are 3, 7, 31, 63, 127, and 255.

DEFAULT VALUE:
    The default value is 255, because RTEMS must support 256 priority levels to
    be compliant with various standards. These priorities range from zero (0)
    to 255.

DESCRIPTION:
   This configuration parameter specified the maximum numeric priority of any
   task in the system and one less that the number of priority levels in the
   system.

   Reducing the number of priorities in the system reduces the amount of memory
   allocated from the RTEMS Workspace.

NOTES:
   The numerically greatest priority is the logically lowest priority in the
   system and will thus be used by the IDLE task.

   Priority zero (0) is reserved for internal use by RTEMS and is not available
   to applications.

   With some schedulers, reducing the number of priorities can reduce the
   amount of memory used by the scheduler. For example, the Deterministic
   Priority Scheduler (DPS) used by default uses three pointers of storage per
   priority level. Reducing the number of priorities from 256 levels to
   sixteen (16) can reduce memory usage by about three (3) kilobytes.

.. COMMENT: === CONFIGURE_MAXIMUM_THREAD_NAME_SIZE ===

.. _Specifying the Maximum Thread Name Size

Specifying the Maximum Thread Name Size
---------------------------------------
.. index:: CONFIGURE_MAXIMUM_THREAD_NAME_SIZE
.. index:: maximum thread name size

CONSTANT:
    ``CONFIGURE_MAXIMUM_THREAD_NAME_SIZE``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    No restrictions.

DEFAULT VALUE:
    The default value is 16.  This value was chosen for Linux compatibility,
    see
    `PTHREAD_SETNAME_NP(3) <http://man7.org/linux/man-pages/man3/pthread_setname_np.3.html>`_.

DESCRIPTION:
   This configuration parameter specifies the maximum thread name size
   including the terminating `NUL` character.

NOTE:
   The size of the thread control block is increased by the maximum thread name
   size.  This configuration option is available since RTEMS 4.12.

.. COMMENT: === CONFIGURE_MINIMUM_TASK_STACK_SIZE ===

.. _Specifying the Minimum Task Size:

Specifying the Minimum Task Size
--------------------------------
.. index:: CONFIGURE_MINIMUM_TASK_STACK_SIZE
.. index:: minimum task stack size

CONSTANT:
    ``CONFIGURE_MINIMUM_TASK_STACK_SIZE``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    This is not defined by default, which sets the executive to the recommended
    minimum stack size for this processor.

DESCRIPTION:
    The configuration parameter is set to the number of bytes the application
    wants the minimum stack size to be for every task or thread in the system.

    Adjusting this parameter should be done with caution. Examining the actual
    usage using the Stack Checker Usage Reporting facility is recommended.

NOTES:
    This parameter can be used to lower the minimum from that recommended. This
    can be used in low memory systems to reduce memory consumption for
    stacks. However, this must be done with caution as it could increase the
    possibility of a blown task stack.

    This parameter can be used to increase the minimum from that
    recommended. This can be used in higher memory systems to reduce the risk
    of stack overflow without performing analysis on actual consumption.

.. COMMENT: === CONFIGURE_INTERRUPT_STACK_SIZE ===

.. _Configuring the Size of the Interrupt Stack:

Configuring the Size of the Interrupt Stack
-------------------------------------------
.. index:: CONFIGURE_INTERRUPT_STACK_SIZE
.. index:: interrupt stack size

CONSTANT:
    ``CONFIGURE_INTERRUPT_STACK_SIZE``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is CONFIGURE_MINIMUM_TASK_STACK_SIZE, which is the
    minimum interrupt stack size.

DESCRIPTION:
    ``CONFIGURE_INTERRUPT_STACK_SIZE`` is set to the size of the interrupt
    stack.  The interrupt stack size is often set by the BSP but since this
    memory may be allocated from the RTEMS Workspace, it must be accounted for.

NOTES:
    In some BSPs, changing this constant does NOT change the size of the
    interrupt stack, only the amount of memory reserved for it.

    Patches which result in this constant only being used in memory
    calculations when the interrupt stack is intended to be allocated from the
    RTEMS Workspace would be welcomed by the RTEMS Project.

.. COMMENT: === CONFIGURE_EXTRA_TASK_STACKS ===

.. _Reserve Task/Thread Stack Memory Above Minimum:

Reserve Task/Thread Stack Memory Above Minimum
----------------------------------------------
.. index:: CONFIGURE_EXTRA_TASK_STACKS
.. index:: memory for task tasks

CONSTANT:
    ``CONFIGURE_EXTRA_TASK_STACKS``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    Undefined or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    This configuration parameter is set to the number of bytes the applications
    wishes to add to the task stack requirements calculated by
    ``<rtems/confdefs.h>``.

NOTES:
    This parameter is very important.  If the application creates tasks with
    stacks larger then the minimum, then that memory is NOT accounted for by
    ``<rtems/confdefs.h>``.

.. COMMENT: === CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY ===

.. _Automatically Zeroing the RTEMS Workspace and C Program Heap:

Automatically Zeroing the RTEMS Workspace and C Program Heap
------------------------------------------------------------
.. index:: CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY
.. index:: clear C Program Heap
.. index:: clear RTEMS Workspace
.. index:: zero C Program Heap
.. index:: zero RTEMS Workspace

CONSTANT:
    ``CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default, unless overridden by the BSP.  The default
    is *NOT* to zero out the RTEMS Workspace or C Program Heap.

DESCRIPTION:
    This macro indicates whether RTEMS should zero the RTEMS Workspace and C
    Program Heap as part of its initialization.  If defined, the memory regions
    are zeroed.  Otherwise, they are not.

NOTES:
    Zeroing memory can add significantly to system boot time. It is not
    necessary for RTEMS but is often assumed by support libraries.

.. COMMENT: === CONFIGURE_STACK_CHECKER_ENABLED ===

.. _Enable The Task Stack Usage Checker:

Enable The Task Stack Usage Checker
-----------------------------------
.. index:: CONFIGURE_STACK_CHECKER_ENABLED

CONSTANT:
    ``CONFIGURE_STACK_CHECKER_ENABLED``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default, and thus stack checking is disabled.

DESCRIPTION:
    This configuration parameter is defined when the application wishes to
    enable run-time stack bounds checking.

NOTES:
    In 4.9 and older, this configuration parameter was named ``STACK_CHECKER_ON``.

    This increases the time required to create tasks as well as adding overhead
    to each context switch.

.. COMMENT: === CONFIGURE_INITIAL_EXTENSIONS ===

.. _CONFIGURE_INITIAL_EXTENSIONS:

Specify Application Specific User Extensions
--------------------------------------------
.. index:: CONFIGURE_INITIAL_EXTENSIONS

CONSTANT:
    ``CONFIGURE_INITIAL_EXTENSIONS``

DATA TYPE:
    List of user extension initializers (``rtems_extensions_table``).

RANGE:
    Undefined or a list of one or more user extensions.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    If ``CONFIGURE_INITIAL_EXTENSIONS`` is defined by the application, then
    this application specific set of initial extensions will be placed in the
    initial extension table.

NOTES:
    None.

.. COMMENT: === Custom Stack Allocator ===

Configuring Custom Task Stack Allocation
========================================

RTEMS allows the application or BSP to define its own allocation and
deallocation methods for task stacks. This can be used to place task stacks in
special areas of memory or to utilize a Memory Management Unit so that stack
overflows are detected in hardware.

.. COMMENT: === CONFIGURE_TASK_STACK_ALLOCATOR_INIT ===

.. _Custom Task Stack Allocator Initialization:

Custom Task Stack Allocator Initialization
------------------------------------------
.. index:: CONFIGURE_TASK_STACK_ALLOCATOR_INIT

CONSTANT:
    ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT``

DATA TYPE:
    Function pointer.

RANGE:
    Undefined, NULL or valid function pointer.

DEFAULT VALUE:
    The default value is NULL, which indicates that task stacks will be
    allocated from the RTEMS Workspace.

DESCRIPTION:
    ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT`` configures the initialization
    method for an application or BSP specific task stack allocation
    implementation.

NOTES:
    A correctly configured system must configure the following to be consistent:

- ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT``

- ``CONFIGURE_TASK_STACK_ALLOCATOR``

- ``CONFIGURE_TASK_STACK_DEALLOCATOR``

.. COMMENT: === CONFIGURE_TASK_STACK_ALLOCATOR ===

.. _Custom Task Stack Allocator:

Custom Task Stack Allocator
---------------------------
.. index:: CONFIGURE_TASK_STACK_ALLOCATOR

.. index:: task stack allocator

CONSTANT:
    ``CONFIGURE_TASK_STACK_ALLOCATOR``

DATA TYPE:
    Function pointer.

RANGE:
    Undefined or valid function pointer.

DEFAULT VALUE:
    The default value is ``_Workspace_Allocate``, which indicates that task
    stacks will be allocated from the RTEMS Workspace.

DESCRIPTION:
    ``CONFIGURE_TASK_STACK_ALLOCATOR`` may point to a user provided routine to
    allocate task stacks.

NOTES:
    A correctly configured system must configure the following to be consistent:

- ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT``

- ``CONFIGURE_TASK_STACK_ALLOCATOR``

- ``CONFIGURE_TASK_STACK_DEALLOCATOR``

.. COMMENT: === CONFIGURE_TASK_STACK_DEALLOCATOR ===

.. _Custom Task Stack Deallocator:

Custom Task Stack Deallocator
-----------------------------
.. index:: CONFIGURE_TASK_STACK_DEALLOCATOR
.. index:: task stack deallocator

CONSTANT:
    ``CONFIGURE_TASK_STACK_DEALLOCATOR``

DATA TYPE:
    Function pointer.

RANGE:
    Undefined or valid function pointer.

DEFAULT VALUE:
    The default value is ``_Workspace_Free``, which indicates that task stacks
    will be allocated from the RTEMS Workspace.

DESCRIPTION:
    ``CONFIGURE_TASK_STACK_DEALLOCATOR`` may point to a user provided routine
    to free task stacks.

NOTES:
    A correctly configured system must configure the following to be consistent:

- ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT``

- ``CONFIGURE_TASK_STACK_ALLOCATOR``

- ``CONFIGURE_TASK_STACK_DEALLOCATOR``

.. COMMENT: === Classic API Message Buffers ===

Configuring Memory for Classic API Message Buffers
==================================================

This section describes the configuration parameters related to specifying the
amount of memory reserved for Classic API Message Buffers.

.. COMMENT: === CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE ===

.. _Calculate Memory for a Single Classic Message API Message Queue:

Calculate Memory for a Single Classic Message API Message Queue
---------------------------------------------------------------
.. index:: CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE
.. index:: memory for a single message queue's buffers

CONSTANT:
    ``CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE(max_messages, size_per)``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is None.

DESCRIPTION:
    This is a helper macro which is used to assist in computing the total
    amount of memory required for message buffers.  Each message queue will
    have its own configuration with maximum message size and maximum number of
    pending messages.

    The interface for this macro is as follows:

    .. code-block:: c

        CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE(max_messages, size_per)

    Where ``max_messages`` is the maximum number of pending messages and
    ``size_per`` is the size in bytes of the user message.

NOTES:

    This macro is only used in support of ``CONFIGURE_MESSAGE_BUFFER_MEMORY``.

.. COMMENT: === CONFIGURE_MESSAGE_BUFFER_MEMORY ===

.. _Reserve Memory for All Classic Message API Message Queues:

Reserve Memory for All Classic Message API Message Queues
---------------------------------------------------------
.. index:: CONFIGURE_MESSAGE_BUFFER_MEMORY
.. index:: configure message queue buffer memory

CONSTANT:
    ``CONFIGURE_MESSAGE_BUFFER_MEMORY``

DATA TYPE:
    integer summation macro

RANGE:
    undefined (zero) or calculation resulting in a positive integer

DEFAULT VALUE:
    This is not defined by default, and zero (0) memory is reserved.

DESCRIPTION:
    This macro is set to the number of bytes the application requires to be
    reserved for pending Classic API Message Queue buffers.

NOTES:
    The following illustrates how the help macro
    ``CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE`` can be used to assist in
    calculating the message buffer memory required.  In this example, there are
    two message queues used in this application.  The first message queue has
    maximum of 24 pending messages with the message structure defined by the
    type ``one_message_type``.  The other message queue has maximum of 500
    pending messages with the message structure defined by the type
    ``other_message_type``.

    .. code-block:: c

        #define CONFIGURE_MESSAGE_BUFFER_MEMORY \
                    (CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE( \
                         24, sizeof(one_message_type) \
                     ) + \
                     CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE( \
                         500, sizeof(other_message_type) \
                     )

.. COMMENT: === Seldom Used Configuration Parameters ===

Seldom Used Configuration Parameters
====================================

This section describes configuration parameters supported by
``<rtems/confdefs.h>`` which are seldom used by applications. These parameters
tend to be oriented to debugging system configurations and providing
work-arounds when the memory estimated by ``<rtems/confdefs.h>`` is incorrect.

.. COMMENT: === CONFIGURE_MEMORY_OVERHEAD ===

.. _Specify Memory Overhead:

Specify Memory Overhead
-----------------------
.. index:: CONFIGURE_MEMORY_OVERHEAD

CONSTANT:
    ``CONFIGURE_MEMORY_OVERHEAD``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    This parameter is set to the number of kilobytes the application wishes to
    add to the requirements calculated by ``<rtems/confdefs.h>``.

NOTES:
    This configuration parameter should only be used when it is suspected that
    a bug in ``<rtems/confdefs.h>`` has resulted in an underestimation.
    Typically the memory allocation will be too low when an application does
    not account for all message queue buffers or task stacks.

.. COMMENT: === CONFIGURE_HAS_OWN_CONFIGURATION_TABLE ===

.. _Do Not Generate Configuration Information:

Do Not Generate Configuration Information
-----------------------------------------
.. index:: CONFIGURE_HAS_OWN_CONFIGURATION_TABLE

CONSTANT:
    ``CONFIGURE_HAS_OWN_CONFIGURATION_TABLE``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    This configuration parameter should only be defined if the application is
    providing their own complete set of configuration tables.

NOTES:
    None.

.. COMMENT: === C Library Support Configuration ===

C Library Support Configuration
===============================

This section defines the file system and IO library related configuration
parameters supported by ``<rtems/confdefs.h>``.

.. COMMENT: === CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS ===

.. _Specify Maximum Number of File Descriptors:

Specify Maximum Number of File Descriptors
------------------------------------------
.. index:: CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS
.. index:: maximum file descriptors

CONSTANT:
    ``CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    If ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER`` is defined, then the
    default value is 3, otherwise the default value is 0.  Three file
    descriptors allows RTEMS to support standard input, output, and error I/O
    streams on ``/dev/console``.

DESCRIPTION:
    This configuration parameter is set to the maximum number of file like
    objects that can be concurrently open.

NOTES:
    None.

.. COMMENT: === CONFIGURE_TERMIOS_DISABLED ===

.. _Disable POSIX Termios Support:

Disable POSIX Termios Support
-----------------------------
.. index:: CONFIGURE_TERMIOS_DISABLED

CONSTANT:
    ``CONFIGURE_TERMIOS_DISABLED``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default, and resources are reserved for the termios
    functionality.

DESCRIPTION:
    This configuration parameter is defined if the software implementing POSIX
    termios functionality is not going to be used by this application.

NOTES:
    The termios support library should not be included in an application
    executable unless it is directly referenced by the application or a device
    driver.

.. COMMENT: === CONFIGURE_NUMBER_OF_TERMIOS_PORTS ===

.. _Specify Maximum Termios Ports:

Specify Maximum Termios Ports
-----------------------------
.. index:: CONFIGURE_NUMBER_OF_TERMIOS_PORTS

CONSTANT:
    ``CONFIGURE_NUMBER_OF_TERMIOS_PORTS``

DATA TYPE:
    Unsigned integer.

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 1, so a console port can be used.

DESCRIPTION:
    This configuration parameter is set to the number of ports using the
    termios functionality.  Each concurrently active termios port requires
    resources.

NOTES:
    If the application will be using serial ports including, but not limited
    to, the Console Device
    (e.g. ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER``), then it is highly
    likely that this configuration parameter should NOT be is defined.

.. COMMENT: === File System Configuration Parameters ===

File System Configuration Parameters
====================================

This section defines File System related configuration parameters.

.. COMMENT: === CONFIGURE_HAS_OWN_MOUNT_TABLE ===

.. _Providing Application Specific Mount Table:

Providing Application Specific Mount Table
------------------------------------------
.. index:: CONFIGURE_HAS_OWN_MOUNT_TABLE

CONSTANT:
    ``CONFIGURE_HAS_OWN_MOUNT_TABLE``

DATA TYPE:
    Undefined or an array of type ``rtems_filesystem_mount_table_t``.

RANGE:
    Undefined or an array of type ``rtems_filesystem_mount_table_t``.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    This configuration parameter is defined when the application provides their
    own filesystem mount table.  The mount table is an array of
    ``rtems_filesystem_mount_table_t`` entries pointed to by the global
    variable ``rtems_filesystem_mount_table``.  The number of entries in this
    table is in an integer variable named ``rtems_filesystem_mount_table_t``.

.. COMMENT: XXX - is the variable name for the count right?

NOTES:
    None.

.. COMMENT: XXX - Please provide an example

.. COMMENT: === CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM ===

.. _Configure devFS as Root File System:

Configure devFS as Root File System
-----------------------------------
.. index:: CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM

CONSTANT:
    ``CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default. If no other root file system configuration
    parameters are specified, the IMFS will be used as the root file system.

DESCRIPTION:
    This configuration parameter is defined if the application wishes to use
    the device-only filesytem as the root file system.

NOTES:
    The device-only filesystem supports only device nodes and is smaller in
    executable code size than the full IMFS and miniIMFS.

    The devFS is comparable in functionality to the pseudo-filesystem name
    space provided before RTEMS release 4.5.0.

.. COMMENT: === CONFIGURE_MAXIMUM_DEVICES ===

.. _Specifying Maximum Devices for devFS:

Specifying Maximum Devices for devFS
------------------------------------
.. index:: CONFIGURE_MAXIMUM_DEVICES

CONSTANT:
    ``CONFIGURE_MAXIMUM_DEVICES``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    If ``BSP_MAXIMUM_DEVICES`` is defined, then the default value is
    ``BSP_MAXIMUM_DEVICES``, otherwise the default value is 4.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_DEVICES`` is defined to the number of individual
    devices that may be registered in the device file system (devFS).

NOTES:
    This option is specific to the device file system (devFS) and should not be
    confused with the ``CONFIGURE_MAXIMUM_DRIVERS`` option.  This parameter
    only impacts the devFS and thus is only used by ``<rtems/confdefs.h>`` when
    ``CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM`` is specified.

.. COMMENT: === CONFIGURE_APPLICATION_DISABLE_FILESYSTEM ===

.. _Disable File System Support:

Disable File System Support
---------------------------
.. index:: CONFIGURE_APPLICATION_DISABLE_FILESYSTEM

CONSTANT:
    ``CONFIGURE_APPLICATION_DISABLE_FILESYSTEM``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default. If no other root file system configuration
    parameters are specified, the IMFS will be used as the root file system.

DESCRIPTION:
    This configuration parameter is defined if the application dose not intend
    to use any kind of filesystem support. This include the device
    infrastructure necessary to support ``printf()``.

NOTES:
    None.

.. COMMENT: === CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM ===

.. _Use a Root IMFS with a Minimalistic Feature Set:

Use a Root IMFS with a Minimalistic Feature Set
-----------------------------------------------
.. index:: CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM

CONSTANT:
    ``CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the following
    configuration options will be defined as well

    - ``CONFIGURE_IMFS_DISABLE_CHMOD``,

    - ``CONFIGURE_IMFS_DISABLE_CHOWN``,

    - ``CONFIGURE_IMFS_DISABLE_UTIME``,

    - ``CONFIGURE_IMFS_DISABLE_LINK``,

    - ``CONFIGURE_IMFS_DISABLE_SYMLINK``,

    - ``CONFIGURE_IMFS_DISABLE_READLINK``,

    - ``CONFIGURE_IMFS_DISABLE_RENAME``, and

    - ``CONFIGURE_IMFS_DISABLE_UNMOUNT``.

.. COMMENT: === CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK ===

.. _Specify Block Size for IMFS:

Specify Block Size for IMFS
---------------------------
.. index:: CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK

CONSTANT:
    ``CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Valid values for this configuration parameter are a power of two (2)
    between 16 and 512 inclusive.  In other words, valid values are 16, 32, 64,
    128, 256,and 512.

DEFAULT VALUE:
    The default IMFS block size is 128 bytes.

DESCRIPTION:
    This configuration parameter specifies the block size for in-memory files
    managed by the IMFS. The configured block size has two impacts. The first
    is the average amount of unused memory in the last block of each file. For
    example, when the block size is 512, on average one-half of the last block
    of each file will remain unused and the memory is wasted. In contrast, when
    the block size is 16, the average unused memory per file is only 8
    bytes. However, it requires more allocations for the same size file and
    thus more overhead per block for the dynamic memory management.

    Second, the block size has an impact on the maximum size file that can be
    stored in the IMFS. With smaller block size, the maximum file size is
    correspondingly smaller. The following shows the maximum file size possible
    based on the configured block size:

    - when the block size is 16 bytes, the maximum file size is 1,328 bytes.

    - when the block size is 32 bytes, the maximum file size is 18,656 bytes.

    - when the block size is 64 bytes, the maximum file size is 279,488 bytes.

    - when the block size is 128 bytes, the maximum file size is 4,329,344 bytes.

    - when the block size is 256 bytes, the maximum file size is 68,173,568 bytes.

    - when the block size is 512 bytes, the maximum file size is 1,082,195,456
      bytes.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_CHOWN ===

.. _Disable Change Owner Support of Root IMFS:

Disable Change Owner Support of Root IMFS
-----------------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_CHOWN

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_CHOWN``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to change
    the owner is disabled in the root IMFS.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_CHMOD ===

.. _Disable Change Mode Support of Root IMFS:

Disable Change Mode Support of Root IMFS
----------------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_CHMOD

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_CHMOD``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to change
    the mode is disabled in the root IMFS.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_UTIME ===

.. _Disable Change Times Support of Root IMFS:

Disable Change Times Support of Root IMFS
-----------------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_UTIME

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_UTIME``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to change
    times is disabled in the root IMFS.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_LINK ===

.. _Disable Create Hard Link Support of Root IMFS:

Disable Create Hard Link Support of Root IMFS
---------------------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_LINK

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_LINK``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to create
    hard links is disabled in the root IMFS.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_SYMLINK ===

.. _Disable Create Symbolic Link Support of Root IMFS:

Disable Create Symbolic Link Support of Root IMFS
-------------------------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_SYMLINK

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_SYMLINK``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to create
    symbolic links is disabled in the root IMFS.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_READLINK ===

.. _Disable Read Symbolic Link Support of Root IMFS:

Disable Read Symbolic Link Support of Root IMFS
-----------------------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_READLINK

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_READLINK``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to read
    symbolic links is disabled in the root IMFS.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_RENAME ===

.. _Disable Rename Support of Root IMFS:

Disable Rename Support of Root IMFS
-----------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_RENAME

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_RENAME``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to rename
    nodes is disabled in the root IMFS.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_READDIR ===

.. _Disable Directory Read Support of Root IMFS:

Disable Directory Read Support of Root IMFS
-------------------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_READDIR

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_READDIR``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to read a
    directory is disabled in the root IMFS.  It is still possible to open nodes
    in a directory.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_MOUNT ===

.. _Disable Mount Support of Root IMFS:

Disable Mount Support of Root IMFS
----------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_MOUNT

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_MOUNT``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to mount
    other file systems is disabled in the root IMFS.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_UNMOUNT ===

.. _Disable Unmount Support of Root IMFS:

Disable Unmount Support of Root IMFS
------------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_UNMOUNT

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_UNMOUNT``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to unmount
    file systems is disabled in the root IMFS.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_MKNOD ===

.. _Disable Make Nodes Support of Root IMFS:

Disable Make Nodes Support of Root IMFS
---------------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_MKNOD

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_MKNOD``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to make
    directories, devices, regular files and FIFOs is disabled in the root IMFS.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_MKNOD_FILE ===

.. _Disable Make Files Support of Root IMFS:

Disable Make Files Support of Root IMFS
---------------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_MKNOD_FILE

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_MKNOD_FILE``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to make
    regular files is disabled in the root IMFS.

.. COMMENT: === CONFIGURE_IMFS_DISABLE_RMNOD ===

.. _Disable Remove Nodes Support of Root IMFS:

Disable Remove Nodes Support of Root IMFS
-----------------------------------------
.. index:: CONFIGURE_IMFS_DISABLE_RMNOD

CONSTANT:
    ``CONFIGURE_IMFS_DISABLE_RMNOD``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    In case this configuration option is defined, then the support to remove
    nodes is disabled in the root IMFS.

.. COMMENT: === Block Device Cache Configuration ===

Block Device Cache Configuration
================================

This section defines Block Device Cache (bdbuf) related configuration
parameters.

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_LIBBLOCK ===

.. _Enable Block Device Cache:

Enable Block Device Cache
-------------------------
.. index:: CONFIGURE_APPLICATION_NEEDS_LIBBLOCK

CONSTANT:
    ``CONFIGURE_APPLICATION_NEEDS_LIBBLOCK``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    Provides a Block Device Cache configuration.

NOTES:
    Each option of the Block Device Cache configuration can be explicitly set
    by the user with the configuration options below.  The Block Device Cache
    is used for example by the RFS and DOSFS file systems.

.. COMMENT: === CONFIGURE_BDBUF_CACHE_MEMORY_SIZE ===

.. _Size of the Cache Memory:

Size of the Cache Memory
------------------------
.. index:: CONFIGURE_BDBUF_CACHE_MEMORY_SIZE

CONSTANT:
    ``CONFIGURE_BDBUF_CACHE_MEMORY_SIZE``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is 32768 bytes.

DESCRIPTION:
    Size of the cache memory in bytes.

NOTES:
    None.

.. COMMENT: === CONFIGURE_BDBUF_BUFFER_MIN_SIZE ===

.. _Minimum Size of a Buffer:

Minimum Size of a Buffer
------------------------
.. index:: CONFIGURE_BDBUF_BUFFER_MIN_SIZE

CONSTANT:
    ``CONFIGURE_BDBUF_BUFFER_MIN_SIZE``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is 512 bytes.

DESCRIPTION:
    Defines the minimum size of a buffer in bytes.

NOTES:
    None.

.. COMMENT: === CONFIGURE_BDBUF_BUFFER_MAX_SIZE ===

.. _Maximum Size of a Buffer:

Maximum Size of a Buffer
------------------------
.. index:: CONFIGURE_BDBUF_BUFFER_MAX_SIZE

CONSTANT:
    ``CONFIGURE_BDBUF_BUFFER_MAX_SIZE``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    It must be positive and an integral multiple of the buffer minimum size.

DEFAULT VALUE:
    The default value is 4096 bytes.

DESCRIPTION:
    Defines the maximum size of a buffer in bytes.

NOTES:
    None.

.. COMMENT: === CONFIGURE_SWAPOUT_SWAP_PERIOD ===

.. _Swapout Task Swap Period:

Swapout Task Swap Period
------------------------
.. index:: CONFIGURE_SWAPOUT_SWAP_PERIOD

CONSTANT:
    ``CONFIGURE_SWAPOUT_SWAP_PERIOD``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is 250 milliseconds.

DESCRIPTION:
    Defines the swapout task swap period in milliseconds.

NOTES:
    None.

.. COMMENT: === CONFIGURE_SWAPOUT_BLOCK_HOLD ===

.. _Swapout Task Maximum Block Hold Time:

Swapout Task Maximum Block Hold Time
------------------------------------
.. index:: CONFIGURE_SWAPOUT_BLOCK_HOLD

CONSTANT:
    ``CONFIGURE_SWAPOUT_BLOCK_HOLD``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is 1000 milliseconds.

DESCRIPTION:
    Defines the swapout task maximum block hold time in milliseconds.

NOTES:
    None.

.. COMMENT: === CONFIGURE_SWAPOUT_TASK_PRIORITY ===

.. _Swapout Task Priority:

Swapout Task Priority
---------------------
.. index:: CONFIGURE_SWAPOUT_TASK_PRIORITY

CONSTANT:
    ``CONFIGURE_SWAPOUT_TASK_PRIORITY``

DATA TYPE:
    Task priority (``rtems_task_priority``).

RANGE:
    Valid task priority.

DEFAULT VALUE:
    The default value is 15.

DESCRIPTION:
    Defines the swapout task priority.

NOTES:
    None.

.. COMMENT: === CONFIGURE_BDBUF_MAX_READ_AHEAD_BLOCKS ===

.. _Maximum Blocks per Read-Ahead Request:

Maximum Blocks per Read-Ahead Request
-------------------------------------
.. index:: CONFIGURE_BDBUF_MAX_READ_AHEAD_BLOCKS

CONSTANT:
    ``CONFIGURE_BDBUF_MAX_READ_AHEAD_BLOCKS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    Defines the maximum blocks per read-ahead request.

NOTES:
    A value of 0 disables the read-ahead task (default).  The read-ahead task
    will issue speculative read transfers if a sequential access pattern is
    detected.  This can improve the performance on some systems.

.. COMMENT: === CONFIGURE_BDBUF_MAX_WRITE_BLOCKS ===

.. _Maximum Blocks per Write Request:

Maximum Blocks per Write Request
--------------------------------
.. index:: CONFIGURE_BDBUF_MAX_WRITE_BLOCKS

CONSTANT:
    ``CONFIGURE_BDBUF_MAX_WRITE_BLOCKS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is 16.

DESCRIPTION:
    Defines the maximum blocks per write request.

NOTES:
    None.

.. COMMENT: === CONFIGURE_BDBUF_TASK_STACK_SIZE ===

.. _Task Stack Size of the Block Device Cache Tasks:

Task Stack Size of the Block Device Cache Tasks
-----------------------------------------------
.. index:: CONFIGURE_BDBUF_TASK_STACK_SIZE

CONSTANT:
    ``CONFIGURE_BDBUF_TASK_STACK_SIZE``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is RTEMS_MINIMUM_STACK_SIZE.

DESCRIPTION:
    Defines the task stack size of the Block Device Cache tasks in bytes.

NOTES:
    None.

.. COMMENT: === CONFIGURE_BDBUF_READ_AHEAD_TASK_PRIORITY ===

.. _Read-Ahead Task Priority:

Read-Ahead Task Priority
------------------------
.. index:: CONFIGURE_BDBUF_READ_AHEAD_TASK_PRIORITY

CONSTANT:
    ``CONFIGURE_BDBUF_READ_AHEAD_TASK_PRIORITY``

DATA TYPE:
    Task priority (``rtems_task_priority``).

RANGE:
    Valid task priority.

DEFAULT VALUE:
    The default value is 15.

DESCRIPTION:
    Defines the read-ahead task priority.

NOTES:
    None.

.. COMMENT: === CONFIGURE_SWAPOUT_WORKER_TASKS ===

.. _Swapout Worker Task Count:

Swapout Worker Task Count
-------------------------
.. index:: CONFIGURE_SWAPOUT_WORKER_TASKS

CONSTANT:
    ``CONFIGURE_SWAPOUT_WORKER_TASKS``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    Defines the swapout worker task count.

NOTES:
    None.

.. COMMENT: === CONFIGURE_SWAPOUT_WORKER_TASK_PRIORITY ===

.. _Swapout Worker Task Priority:

Swapout Worker Task Priority
----------------------------
.. index:: CONFIGURE_SWAPOUT_WORKER_TASK_PRIORITY

CONSTANT:
    ``CONFIGURE_SWAPOUT_WORKER_TASK_PRIORITY``

DATA TYPE:
    Task priority (``rtems_task_priority``).

RANGE:
    Valid task priority.

DEFAULT VALUE:
    The default value is 15.

DESCRIPTION:
    Defines the swapout worker task priority.

NOTES:
    None.

.. COMMENT: === BSP Specific Settings ===

BSP Specific Settings
=====================

This section describes BSP specific configuration settings used by
``<rtems/confdefs.h>``.  The BSP specific configuration settings are defined in
``<bsp.h>``.

.. COMMENT: === Disable BSP Settings ===

.. _Disable BSP Configuration Settings:

Disable BSP Configuration Settings
----------------------------------
.. index:: CONFIGURE_DISABLE_BSP_SETTINGS

CONSTANT:
    ``CONFIGURE_DISABLE_BSP_SETTINGS``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    All BSP specific configuration settings can be disabled by the application
    with the ``CONFIGURE_DISABLE_BSP_SETTINGS`` option.

NOTES:
    None.

.. COMMENT: === CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK ===

.. _Specify BSP Supports sbrk():

Specify BSP Supports sbrk()
---------------------------
.. index:: CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK

CONSTANT:
    ``CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This option is BSP specific.

DESCRIPTION:
    This configuration parameter is defined by a BSP to indicate that it does
    not allocate all available memory to the C Program Heap used by the Malloc
    Family of routines.

    If defined, when ``malloc()`` is unable to allocate memory, it will call
    the BSP supplied ``sbrk()`` to obtain more memory.

NOTES:
    This parameter should not be defined by the application. Only the BSP knows
    how it allocates memory to the C Program Heap.

.. COMMENT: === BSP_IDLE_TASK_BODY ===

.. _Specify BSP Specific Idle Task:

Specify BSP Specific Idle Task
------------------------------
.. index:: BSP_IDLE_TASK_BODY

CONSTANT:
    ``BSP_IDLE_TASK_BODY``

DATA TYPE:
    Function pointer.

RANGE:
    Undefined or valid function pointer.

DEFAULT VALUE:
    This option is BSP specific.

DESCRIPTION:
    If ``BSP_IDLE_TASK_BODY`` is defined by the BSP and
    ``CONFIGURE_IDLE_TASK_BODY`` is not defined by the application, then this
    BSP specific idle task body will be used.

NOTES:
    As it has knowledge of the specific CPU model, system controller logic, and
    peripheral buses, a BSP specific IDLE task may be capable of turning
    components off to save power during extended periods of no task activity

.. COMMENT: === BSP_IDLE_TASK_STACK_SIZE ===

.. _Specify BSP Suggested Value for IDLE Task Stack Size:

Specify BSP Suggested Value for IDLE Task Stack Size
----------------------------------------------------
.. index:: BSP_IDLE_TASK_STACK_SIZE

CONSTANT:
    ``BSP_IDLE_TASK_STACK_SIZE``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    Undefined or positive.

DEFAULT VALUE:
    This option is BSP specific.

DESCRIPTION:
    If ``BSP_IDLE_TASK_STACK_SIZE`` is defined by the BSP and
    ``CONFIGURE_IDLE_TASK_STACK_SIZE`` is not defined by the application, then
    this BSP suggested idle task stack size will be used.

NOTES:
    The order of precedence for configuring the IDLE task stack size is:

    - RTEMS default minimum stack size.

    - If defined, then ``CONFIGURE_MINIMUM_TASK_STACK_SIZE``.

    - If defined, then the BSP specific ``BSP_IDLE_TASK_SIZE``.

    - If defined, then the application specified ``CONFIGURE_IDLE_TASK_SIZE``.

.. COMMENT: XXX - add cross references to other related values.

.. COMMENT: === BSP_INITIAL_EXTENSION ===

.. _Specify BSP Specific User Extensions:

Specify BSP Specific User Extensions
------------------------------------
.. index:: BSP_INITIAL_EXTENSION

CONSTANT:
    ``BSP_INITIAL_EXTENSION``

DATA TYPE:
    List of user extension initializers (``rtems_extensions_table``).

RANGE:
    Undefined or a list of user extension initializers.

DEFAULT VALUE:
    This option is BSP specific.

DESCRIPTION:
    If ``BSP_INITIAL_EXTENSION`` is defined by the BSP, then this BSP specific
    initial extension will be placed as the last entry in the initial extension
    table.

NOTES:
    None.

.. COMMENT: === BSP_INTERRUPT_STACK_SIZE ===

.. _Specifying BSP Specific Interrupt Stack Size:

Specifying BSP Specific Interrupt Stack Size
--------------------------------------------
.. index:: BSP_INTERRUPT_STACK_SIZE

CONSTANT:
    ``BSP_INTERRUPT_STACK_SIZE``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    Undefined or positive.

DEFAULT VALUE:
    This option is BSP specific.

DESCRIPTION:
    If ``BSP_INTERRUPT_STACK_SIZE`` is defined by the BSP and
    ``CONFIGURE_INTERRUPT_STACK_SIZE`` is not defined by the application, then
    this BSP specific interrupt stack size will be used.

NOTES:
    None.

.. COMMENT: === BSP_MAXIMUM_DEVICES ===

.. _Specifying BSP Specific Maximum Devices:

Specifying BSP Specific Maximum Devices
---------------------------------------
.. index:: BSP_MAXIMUM_DEVICES

CONSTANT:
    ``BSP_MAXIMUM_DEVICES``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    Undefined or positive.

DEFAULT VALUE:
    This option is BSP specific.

DESCRIPTION:
    If ``BSP_MAXIMUM_DEVICES`` is defined by the BSP and
    ``CONFIGURE_MAXIMUM_DEVICES`` is not defined by the application, then this
    BSP specific maximum device count will be used.

NOTES:
    This option is specific to the device file system (devFS) and should not be
    confused with the ``CONFIGURE_MAXIMUM_DRIVERS`` option.  This parameter
    only impacts the devFS and thus is only used by ``<rtems/confdefs.h>`` when
    ``CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM`` is specified.

.. COMMENT: === BSP_ZERO_WORKSPACE_AUTOMATICALLY ===

.. _BSP Recommends RTEMS Workspace be Cleared:

BSP Recommends RTEMS Workspace be Cleared
-----------------------------------------
.. index:: BSP_ZERO_WORKSPACE_AUTOMATICALLY

CONSTANT:
    ``BSP_ZERO_WORKSPACE_AUTOMATICALLY``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This option is BSP specific.

DESCRIPTION:
    If ``BSP_ZERO_WORKSPACE_AUTOMATICALLY`` is defined by the BSP and
    ``CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY`` is not defined by the
    application, then the workspace will be zeroed automatically.

NOTES:
    Zeroing memory can add significantly to system boot time. It is not
    necessary for RTEMS but is often assumed by support libraries.

.. COMMENT: === CONFIGURE_BSP_PREREQUISITE_DRIVERS ===

.. _Specify BSP Prerequisite Drivers:

Specify BSP Prerequisite Drivers
--------------------------------
.. index:: CONFIGURE_BSP_PREREQUISITE_DRIVERS

CONSTANT:
    ``CONFIGURE_BSP_PREREQUISITE_DRIVERS``

DATA TYPE:
    List of device driver initializers (``rtems_driver_address_table``).

RANGE:
    Undefined or array of device drivers.

DEFAULT VALUE:
    This option is BSP specific.

DESCRIPTION:
    ``CONFIGURE_BSP_PREREQUISITE_DRIVERS`` is defined if the BSP has device
    drivers it needs to include in the Device Driver Table.  This should be
    defined to the set of device driver entries that will be placed in the
    table at the *FRONT* of the Device Driver Table and initialized before any
    other drivers *INCLUDING* any application prerequisite drivers.

NOTES:
    ``CONFIGURE_BSP_PREREQUISITE_DRIVERS`` is typically used by BSPs to
    configure common infrastructure such as bus controllers or probe for
    devices.

.. COMMENT: === Idle Task Configuration ===

Idle Task Configuration
=======================

This section defines the IDLE task related configuration parameters supported
by ``<rtems/confdefs.h>``.

.. COMMENT: === CONFIGURE_IDLE_TASK_BODY ===

.. _Specify Application Specific Idle Task Body:

Specify Application Specific Idle Task Body
-------------------------------------------
.. index:: CONFIGURE_IDLE_TASK_BODY

CONSTANT:
    ``CONFIGURE_IDLE_TASK_BODY``

DATA TYPE:
    Function pointer.

RANGE:
    Undefined or valid function pointer.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_IDLE_TASK_BODY`` is set to the function name corresponding to
    the application specific IDLE thread body.  If not specified, the BSP or
    RTEMS default IDLE thread body will be used.

NOTES:
    None.

.. COMMENT: === CONFIGURE_IDLE_TASK_STACK_SIZE ===

.. _Specify Idle Task Stack Size:

Specify Idle Task Stack Size
----------------------------
.. index:: CONFIGURE_IDLE_TASK_STACK_SIZE

CONSTANT:
    ``CONFIGURE_IDLE_TASK_STACK_SIZE``

DATA TYPE:
    Unsigned integer (``size_t``).

RANGE:
    Undefined or positive.

DEFAULT VALUE:
    The default value is RTEMS_MINIMUM_STACK_SIZE.

DESCRIPTION:
    ``CONFIGURE_IDLE_TASK_STACK_SIZE`` is set to the desired stack size for the
    IDLE task.

NOTES:
    None.

.. COMMENT: === CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION ===

.. _Specify Idle Task Performs Application Initialization:

Specify Idle Task Performs Application Initialization
-----------------------------------------------------
.. index:: CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION

CONSTANT:
    ``CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default, the user is assumed to provide one or more
    initialization tasks.

DESCRIPTION:
    ``CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION`` is set to indicate that the
    user has configured *NO* user initialization tasks or threads and that the
    user provided IDLE task will perform application initialization and then
    transform itself into an IDLE task.

NOTES:
    If you use this option be careful, the user IDLE task *CANNOT* block at all
    during the initialization sequence.  Further, once application
    initialization is complete, it must make itself preemptible and enter an
    IDLE body loop.

    The IDLE task must run at the lowest priority of all tasks in the system.

.. COMMENT: === Scheduler Algorithm Configuration ===

Scheduler Algorithm Configuration
=================================

This section defines the configuration parameters related to selecting a
scheduling algorithm for an application.  For the schedulers built into RTEMS,
the configuration is straightforward.  All that is required is to define the
configuration macro which specifies which scheduler you want for in your
application.  The currently available schedulers are:

The pluggable scheduler interface also enables the user to provide their own
scheduling algorithm.  If you choose to do this, you must define multiple
configuration macros.

.. COMMENT: === CONFIGURE_SCHEDULER_PRIORITY ===

.. _Use Deterministic Priority Scheduler:

Use Deterministic Priority Scheduler
------------------------------------
.. index:: CONFIGURE_SCHEDULER_PRIORITY

CONSTANT:
    ``CONFIGURE_SCHEDULER_PRIORITY``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is defined by default.  This is the default scheduler and specifying
    this configuration parameter is redundant.

DESCRIPTION:
    The Deterministic Priority Scheduler is the default scheduler in RTEMS for
    uni-processor applications and is designed for predictable performance
    under the highest loads.  It can block or unblock a thread in a constant
    amount of time.  This scheduler requires a variable amount of memory based
    upon the number of priorities configured in the system.

NOTES:
    This scheduler may be explicitly selected by defining
    ``CONFIGURE_SCHEDULER_PRIORITY`` although this is equivalent to the default
    behavior.

.. COMMENT: === CONFIGURE_SCHEDULER_SIMPLE ===

.. _Use Simple Priority Scheduler:

Use Simple Priority Scheduler
-----------------------------
.. index:: CONFIGURE_SCHEDULER_SIMPLE

CONSTANT:
    ``CONFIGURE_SCHEDULER_SIMPLE``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    When defined, the Simple Priority Scheduler is used at the thread
    scheduling algorithm. This is an alternative scheduler in RTEMS.  It is
    designed to provide the same task scheduling behaviour as the Deterministic
    Priority Scheduler while being simpler in implementation and uses less
    memory for data management.  It maintains a single sorted list of all ready
    threads.  Thus blocking or unblocking a thread is not a constant time
    operation with this scheduler.

    This scheduler may be explicitly selected by defining
    ``CONFIGURE_SCHEDULER_SIMPLE``.

NOTES:
    This scheduler is appropriate for use in small systems where RAM is limited.

.. COMMENT: === CONFIGURE_SCHEDULER_EDF ===

.. _Use Earliest Deadline First Scheduler:

Use Earliest Deadline First Scheduler
-------------------------------------
.. index:: CONFIGURE_SCHEDULER_EDF

CONSTANT:
    ``CONFIGURE_SCHEDULER_EDF``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    The Earliest Deadline First Scheduler (EDF) is an alternative scheduler in
    RTEMS for uni-processor applications. The EDF schedules tasks with dynamic
    priorities equal to deadlines. The deadlines are declared using only Rate
    Monotonic manager which handles periodic behavior.  Period is always equal
    to deadline. If a task does not have any deadline declared or the deadline
    is cancelled, the task is considered a background task which is scheduled
    in case no deadline-driven tasks are ready to run.  Moreover, multiple
    background tasks are scheduled according their priority assigned upon
    initialization. All ready tasks reside in a single ready queue.

    This scheduler may be explicitly selected by defining
    ``CONFIGURE_SCHEDULER_EDF``.

NOTES:
    None.

.. COMMENT: === CONFIGURE_SCHEDULER_CBS ===

.. _Use Constant Bandwidth Server Scheduler:

Use Constant Bandwidth Server Scheduler
---------------------------------------
.. index:: CONFIGURE_SCHEDULER_CBS

CONSTANT:
    ``CONFIGURE_SCHEDULER_CBS``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    The Constant Bandwidth Server Scheduler (CBS) is an alternative scheduler
    in RTEMS for uni-processor applications. The CBS is a budget aware
    extension of EDF scheduler. The goal of this scheduler is to ensure
    temporal isolation of tasks. The CBS is equipped with a set of additional
    rules and provides with an extensive API.

    This scheduler may be explicitly selected by defining
    ``CONFIGURE_SCHEDULER_CBS``.

.. COMMENT: XXX - add cross reference to API chapter

NOTES:
    None.

.. COMMENT: === CONFIGURE_SCHEDULER_PRIORITY_SMP ===

.. _Use Deterministic Priority SMP Scheduler:

Use Deterministic Priority SMP Scheduler
----------------------------------------
.. index:: CONFIGURE_SCHEDULER_PRIORITY_SMP

CONSTANT:
    ``CONFIGURE_SCHEDULER_PRIORITY_SMP``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    The Deterministic Priority SMP Scheduler is derived from the Deterministic
    Priority Scheduler but is capable of scheduling threads across multiple
    processors.

    In a configuration with SMP enabled at configure time, it may be explicitly
    selected by defining ``CONFIGURE_SCHEDULER_PRIORITY_SMP``.

NOTES:
    This scheduler is only available when RTEMS is configured with SMP support
    enabled.

    This scheduler is currently the default in SMP configurations and is only
    selected when ``CONFIGURE_SMP_APPLICATION`` is defined.

.. COMMENT: === CONFIGURE_SCHEDULER_SIMPLE_SMP ===

.. _Use Simple SMP Priority Scheduler:

Use Simple SMP Priority Scheduler
---------------------------------
.. index:: CONFIGURE_SCHEDULER_SIMPLE_SMP

CONSTANT:
    ``CONFIGURE_SCHEDULER_SIMPLE_SMP``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    The Simple SMP Priority Scheduler is derived from the Simple Priority
    Scheduler but is capable of scheduling threads across multiple processors.
    It is designed to provide the same task scheduling behaviour as the
    Deterministic Priority Scheduler while distributing threads across multiple
    processors.  Being based upon the Simple Priority Scheduler, it also
    maintains a single sorted list of all ready threads.  Thus blocking or
    unblocking a thread is not a constant time operation with this scheduler.

    In addition, when allocating threads to processors, the algorithm is not
    constant time. This algorithm was not designed with efficiency as a primary
    design goal.  Its primary design goal was to provide an SMP-aware
    scheduling algorithm that is simple to understand.

    In a configuration with SMP enabled at configure time, it may be explicitly
    selected by defining ``CONFIGURE_SCHEDULER_SIMPLE_SMP``.

NOTES:
    This scheduler is only available when RTEMS is configured with SMP support
    enabled.

.. COMMENT: === Configuring a Scheduler Name ===

.. _Configuring a Scheduler Name:

Configuring a Scheduler Name
----------------------------
.. index:: CONFIGURE_SCHEDULER_NAME

CONSTANT:
    ``CONFIGURE_SCHEDULER_NAME``

DATA TYPE:
    RTEMS Name (``rtems_name``).

RANGE:
    Any value.

DEFAULT VALUE:
    The default name is
      - ``"UCBS"`` for the Uni-Processor CBS scheduler,
      - ``"UEDF"`` for the Uni-Processor EDF scheduler,
      - ``"UPD "`` for the Uni-Processor Deterministic Priority scheduler,
      - ``"UPS "`` for the Uni-Processor Simple Priority scheduler,
      - ``"MPA "`` for the Multi-Processor Priority Affinity scheduler, and
      - ``"MPD "`` for the Multi-Processor Deterministic Priority scheduler, and
      - ``"MPS "`` for the Multi-Processor Simple Priority scheduler.

DESCRIPTION:
    Schedulers can be identified via ``rtems_scheduler_ident``.  The name of
    the scheduler is determined by the configuration.

NOTES:
    None.

.. COMMENT: === Configuring a User Scheduler ===

.. _Configuring a User Provided Scheduler:

Configuring a User Provided Scheduler
-------------------------------------
.. index:: CONFIGURE_SCHEDULER_USER

CONSTANT:
    ``CONFIGURE_SCHEDULER_USER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    RTEMS allows the application to provide its own task/thread scheduling
    algorithm. In order to do this, one must define
    ``CONFIGURE_SCHEDULER_USER`` to indicate the application provides its own
    scheduling algorithm. If ``CONFIGURE_SCHEDULER_USER`` is defined then the
    following additional macros must be defined:

    - ``CONFIGURE_SCHEDULER_CONTEXT`` must be defined to a static definition of
      the scheduler context of the user scheduler.

    - ``CONFIGURE_SCHEDULER_CONTROLS`` must be defined to a scheduler control
      initializer for the user scheduler.

    - ``CONFIGURE_SCHEDULER_USER_PER_THREAD`` must be defined to the type of
      the per-thread information of the user scheduler.

NOTES:
    At this time, the mechanics and requirements for writing a new scheduler
    are evolving and not fully documented.  It is recommended that you look at
    the existing Deterministic Priority Scheduler in
    ``cpukit/score/src/schedulerpriority*.c`` for guidance.  For guidance on
    the configuration macros, please examine ``cpukit/sapi/include/confdefs.h``
    for how these are defined for the Deterministic Priority Scheduler.

.. COMMENT: === Configuring Clustered Schedulers ===

.. _Configuring Clustered Schedulers:

Configuring Clustered Schedulers
--------------------------------

Clustered scheduling helps to control the worst-case latencies in a
multi-processor system.  The goal is to reduce the amount of shared state in
the system and thus prevention of lock contention.  Modern multi-processor
systems tend to have several layers of data and instruction caches.  With
clustered scheduling it is possible to honour the cache topology of a system
and thus avoid expensive cache synchronization traffic.

We have clustered scheduling in case the set of processors of a system is
partitioned into non-empty pairwise-disjoint subsets.  These subsets are called
clusters.  Clusters with a cardinality of one are partitions.  Each cluster is
owned by exactly one scheduler instance.  In order to use clustered scheduling
the application designer has to answer two questions.

#. How is the set of processors partitioned into clusters?

#. Which scheduler is used for which cluster?

CONFIGURATION:
    The schedulers in an SMP system are statically configured on RTEMS.
    Firstly the application must select which scheduling algorithms are
    available with the following defines

    - ``CONFIGURE_SCHEDULER_PRIORITY_SMP``,

    - ``CONFIGURE_SCHEDULER_SIMPLE_SMP``, and

    - ``CONFIGURE_SCHEDULER_PRIORITY_AFFINITY_SMP``.

    This is necessary to calculate the per-thread overhead introduced by the
    schedulers.  After these definitions the configuration file must ``#include
    <rtems/scheduler.h>`` to have access to scheduler specific configuration
    macros.  Each scheduler needs a context to store state information at
    run-time.  To provide a context for each scheduler is the next step.  Use
    the following macros to create scheduler contexts

    - ``RTEMS_SCHEDULER_CONTEXT_PRIORITY_SMP(name, prio_count)``,

    - ``RTEMS_SCHEDULER_CONTEXT_SIMPLE_SMP(name)``, and

    - ``RTEMS_SCHEDULER_CONTEXT_PRIORITY_AFFINITY_SMP(name, prio_count)``.

    The ``name`` parameter is used as part of a designator for a global
    variable, so the usual C/C++ designator rules apply.  Additional parameters
    are scheduler specific.  The schedulers are registered in the system via
    the scheduler table.  To create the scheduler table define
    ``CONFIGURE_SCHEDULER_CONTROLS`` to a list of the following scheduler
    control initializers

    - ``RTEMS_SCHEDULER_CONTROL_PRIORITY_SMP(name, obj_name)``,

    - ``RTEMS_SCHEDULER_CONTROL_SIMPLE_SMP(name, obj_name)``, and

    - ``RTEMS_SCHEDULER_CONTROL_PRIORITY_AFFINITY_SMP(name, obj_name)``.

    The ``name`` parameter must correspond to the parameter defining the
    scheduler context.  The ``obj_name`` determines the scheduler object name
    and can be used in ``rtems_scheduler_ident()`` to get the scheduler object
    identifier.

    The last step is to define which processor uses which scheduler.  For this
    purpose a scheduler assignment table must be defined.  The entry count of
    this table must be equal to the configured maximum processors
    (``CONFIGURE_SMP_MAXIMUM_PROCESSORS``).  A processor assignment to a
    scheduler can be optional or mandatory.  The boot processor must have a
    scheduler assigned.  In case the system needs more mandatory processors
    than available then a fatal run-time error will occur.  To specify the
    scheduler assignments define ``CONFIGURE_SMP_SCHEDULER_ASSIGNMENTS`` to a
    list of ``RTEMS_SCHEDULER_ASSIGN(index, attr)`` and
    ``RTEMS_SCHEDULER_ASSIGN_NO_SCHEDULER`` macros.  The ``index`` parameter
    must be a valid index into the scheduler table.  The ``attr`` parameter
    defines the scheduler assignment attributes.  By default a scheduler
    assignment to a processor is optional.  For the scheduler assignment
    attribute use one of the mutually exclusive variants

    - ``RTEMS_SCHEDULER_ASSIGN_DEFAULT``,

    - ``RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY``, and

    - ``RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL``.

    It is possible to add/remove processors to/from scheduler instances at
    run-time, see :ref:`rtems_scheduler_add_processor` and
    :ref:`rtems_scheduler_remove_processor`.

ERRORS:
    In case one of the scheduler indices
    in``CONFIGURE_SMP_SCHEDULER_ASSIGNMENTS`` is invalid a link-time error will
    occur with an undefined reference to ``RTEMS_SCHEDULER_INVALID_INDEX``.

    Some fatal errors may occur in case of scheduler configuration
    inconsistencies or a lack of processors on the system.  The fatal source is
    ``RTEMS_FATAL_SOURCE_SMP``.  None of the errors is internal.

    - ``SMP_FATAL_BOOT_PROCESSOR_NOT_ASSIGNED_TO_SCHEDULER`` - the boot
      processor must have a scheduler assigned.

    - ``SMP_FATAL_MANDATORY_PROCESSOR_NOT_PRESENT`` - there exists a mandatory
      processor beyond the range of physically or virtually available
      processors.  The processor demand must be reduced for this system.

    - ``SMP_FATAL_START_OF_MANDATORY_PROCESSOR_FAILED`` - the start of a
      mandatory processor failed during system initialization.  The system may
      not have this processor at all or it could be a problem with a boot
      loader for example.  Check the ``CONFIGURE_SMP_SCHEDULER_ASSIGNMENTS``
      definition.

    - ``SMP_FATAL_MULTITASKING_START_ON_UNASSIGNED_PROCESSOR`` - it is not
      allowed to start multitasking on a processor with no scheduler assigned.

EXAMPLE:
    The following example shows a scheduler configuration for a hypothetical
    product using two chip variants.  One variant has four processors which is
    used for the normal product line and another provides eight processors for
    the high-performance product line.  The first processor performs hard-real
    time control of actuators and sensors.  The second processor is not used by
    RTEMS at all and runs a Linux instance to provide a graphical user
    interface.  The additional processors are used for a worker thread pool to
    perform data processing operations.

    The processors managed by RTEMS use two Deterministic Priority scheduler
    instances capable of dealing with 256 priority levels.  The scheduler with
    index zero has the name ``"IO "``.  The scheduler with index one has the
    name ``"WORK"``.  The scheduler assignments of the first, third and fourth
    processor are mandatory, so the system must have at least four processors,
    otherwise a fatal run-time error will occur during system startup.  The
    processor assignments for the fifth up to the eighth processor are optional
    so that the same application can be used for the normal and
    high-performance product lines.  The second processor has no scheduler
    assigned and runs Linux.  A hypervisor will ensure that the two systems
    cannot interfere in an undesirable way.

    .. code-block:: c

        #define CONFIGURE_SMP_MAXIMUM_PROCESSORS 8
        #define CONFIGURE_MAXIMUM_PRIORITY 255

        /* Make the scheduler algorithm available */
        #define CONFIGURE_SCHEDULER_PRIORITY_SMP
        #include <rtems/scheduler.h>

        /* Create contexts for the two scheduler instances */
        RTEMS_SCHEDULER_CONTEXT_PRIORITY_SMP(io, CONFIGURE_MAXIMUM_PRIORITY + 1);
        RTEMS_SCHEDULER_CONTEXT_PRIORITY_SMP(work, CONFIGURE_MAXIMUM_PRIORITY + 1);

        /* Define the scheduler table */
        #define CONFIGURE_SCHEDULER_CONTROLS \\
            RTEMS_SCHEDULER_CONTROL_PRIORITY_SMP( \
                io, \
                rtems_build_name('I', 'O', ' ', ' ') \
            ), \
            RTEMS_SCHEDULER_CONTROL_PRIORITY_SMP( \
                work, \
                rtems_build_name('W', 'O', 'R', 'K') \
            )

        /* Define the initial processor to scheduler assignments */
        #define CONFIGURE_SMP_SCHEDULER_ASSIGNMENTS \
            RTEMS_SCHEDULER_ASSIGN(0, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY), \
            RTEMS_SCHEDULER_ASSIGN_NO_SCHEDULER, \
            RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY), \
            RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY), \
            RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL), \
            RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL), \
            RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL), \
            RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL)

.. COMMENT: === SMP Specific Configuration Parameters ===

SMP Specific Configuration Parameters
=====================================

When RTEMS is configured to support SMP target systems, there are other
configuration parameters which apply.

.. COMMENT: XXX - add -enable-smp

.. COMMENT: === CONFIGURE_SMP_APPLICATION ===

.. _Enable SMP Support for Applications:

Enable SMP Support for Applications
-----------------------------------
.. index:: CONFIGURE_SMP_APPLICATION

CONSTANT:
    ``CONFIGURE_SMP_APPLICATION``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_SMP_APPLICATION`` must be defined to enable SMP support for the
    application.

NOTES:
    This define may go away in the future in case all RTEMS components are SMP
    ready.  This configuration define is ignored on uni-processor
    configurations.

.. COMMENT: === CONFIGURE_SMP_MAXIMUM_PROCESSORS ===

.. _Specify Maximum Processors in SMP System:

Specify Maximum Processors in SMP System
----------------------------------------
.. index:: CONFIGURE_SMP_MAXIMUM_PROCESSORS

CONSTANT:
    ``CONFIGURE_SMP_MAXIMUM_PROCESSORS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    The default value is 1, (if CONFIGURE_SMP_APPLICATION is defined).

DESCRIPTION:
    ``CONFIGURE_SMP_MAXIMUM_PROCESSORS`` must be set to the number of
    processors in the SMP configuration.

NOTES:
    If there are more processors available than configured, the rest will be
    ignored.  This configuration define is ignored on uni-processor
    configurations.

.. COMMENT: === Device Driver Table ===

Device Driver Table
===================

This section defines the configuration parameters related to the automatic
generation of a Device Driver Table.  As ``<rtems/confdefs.h>`` only is aware
of a small set of standard device drivers, the generated Device Driver Table is
suitable for simple applications with no custom device drivers.

Note that network device drivers are not configured in the Device Driver Table.

.. COMMENT: === CONFIGURE_MAXIMUM_DRIVERS ===

.. _Specifying the Maximum Number of Device Drivers:

Specifying the Maximum Number of Device Drivers
-----------------------------------------------
.. index:: CONFIGURE_MAXIMUM_DRIVERS

CONSTANT:

    ``CONFIGURE_MAXIMUM_DRIVERS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    This is computed by default, and is set to the number of device drivers
    configured using the ``CONFIGURE_APPLICATIONS_NEEDS_XXX_DRIVER``
    configuration parameters.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_DRIVERS`` is defined as the number of device drivers
    per node.

NOTES:
    If the application will dynamically install device drivers, then this
    configuration parameter must be larger than the number of statically
    configured device drivers. Drivers configured using the
    ``CONFIGURE_APPLICATIONS_NEEDS_XXX_DRIVER`` configuration parameters are
    statically installed.

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER ===

.. _Enable Console Device Driver:

Enable Console Device Driver
----------------------------
.. index:: CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER

CONSTANT:
    ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER`` is defined if the
    application wishes to include the Console Device Driver.

NOTES:
    This device driver is responsible for providing standard input and output
    using */dev/console*.

    BSPs should be constructed in a manner that allows ``printk()`` to work
    properly without the need for the console driver to be configured.

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER ===

.. _Enable Clock Driver:

Enable Clock Driver
-------------------
.. index:: CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER

CONSTANT:
    ``CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER`` is defined if the application
    wishes to include the Clock Device Driver.

NOTES:
    This device driver is responsible for providing a regular interrupt which
    invokes a clock tick directive.

    If neither the Clock Driver not Benchmark Timer is enabled and the
    configuration parameter
    ``CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER`` is not defined, then a
    compile time error will occur.

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER ===

.. _Enable the Benchmark Timer Driver:

Enable the Benchmark Timer Driver
---------------------------------
.. index:: CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER

CONSTANT:
    ``CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER`` is defined if the application
    wishes to include the Timer Driver.  This device driver is used to
    benchmark execution times by the RTEMS Timing Test Suites.

NOTES:
    If neither the Clock Driver not Benchmark Timer is enabled and the
    configuration parameter
    ``CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER`` is not defined, then a
    compile time error will occur.

.. COMMENT: === CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER ===

.. _Specify Clock and Benchmark Timer Drivers Are Not Needed:

Specify Clock and Benchmark Timer Drivers Are Not Needed
--------------------------------------------------------
.. index:: CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER

CONSTANT:
    ``CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER`` is defined when the
    application does *NOT* want the Clock Device Driver and is *NOT* using the
    Timer Driver.  The inclusion or exclusion of the Clock Driver must be
    explicit in user applications.

NOTES:
    This configuration parameter is intended to prevent the common user error
    of using the Hello World example as the baseline for an application and
    leaving out a clock tick source.

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER ===

.. _Enable Real-Time Clock Driver:

Enable Real-Time Clock Driver
-----------------------------
.. index:: CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER

CONSTANT:
    ``CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER`` is defined if the application
    wishes to include the Real-Time Clock Driver.

NOTES:
    Most BSPs do not include support for a real-time clock. This is because
    many boards do not include the required hardware.

    If this is defined and the BSP does not have this device driver, then the
    user will get a link time error for an undefined symbol.

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER ===

.. _Enable the Watchdog Device Driver:

Enable the Watchdog Device Driver
---------------------------------
.. index:: CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER

CONSTANT:
    ``CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER`` is defined if the
    application wishes to include the Watchdog Driver.

NOTES:
    Most BSPs do not include support for a watchdog device driver. This is
    because many boards do not include the required hardware.

    If this is defined and the BSP does not have this device driver, then the
    user will get a link time error for an undefined symbol.

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER ===

.. _Enable the Graphics Frame Buffer Device Driver:

Enable the Graphics Frame Buffer Device Driver
----------------------------------------------
.. index:: CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER

CONSTANT:
    ``CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER`` is defined if the
    application wishes to include the BSP's Frame Buffer Device Driver.

NOTES:
    Most BSPs do not include support for a Frame Buffer Device Driver. This is
    because many boards do not include the required hardware.

    If this is defined and the BSP does not have this device driver, then the
    user will get a link time error for an undefined symbol.

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER ===

.. _Enable Stub Device Driver:

Enable Stub Device Driver
-------------------------
.. index:: CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER

CONSTANT:
    ``CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER`` is defined if the application
    wishes to include the Stub Device Driver.

NOTES:
    This device driver simply provides entry points that return successful and
    is primarily a test fixture. It is supported by all BSPs.

.. COMMENT: === CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS ===

.. _Specify Application Prerequisite Device Drivers:

Specify Application Prerequisite Device Drivers
-----------------------------------------------
.. index:: CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS

CONSTANT:
    ``CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS``

DATA TYPE:
    device driver entry structures

RANGE:
    Undefined or set of device driver entry structures

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS`` is defined if the
    application has device drivers it needs to include in the Device Driver
    Table.  This should be defined to the set of device driver entries that
    will be placed in the table at the *FRONT* of the Device Driver Table and
    initialized before any other drivers *EXCEPT* any BSP prerequisite drivers.

NOTES:
    In some cases, it is used by System On Chip BSPs to support peripheral
    buses beyond those normally found on the System On Chip. For example, this
    is used by one RTEMS system which has implemented a SPARC/ERC32 based board
    with VMEBus. The VMEBus Controller initialization is performed by a device
    driver configured via this configuration parameter.

.. COMMENT: XXX Add example

.. COMMENT: === CONFIGURE_APPLICATION_EXTRA_DRIVERS ===

.. _Specify Extra Application Device Drivers:

Specify Extra Application Device Drivers
----------------------------------------
.. index:: CONFIGURE_APPLICATION_EXTRA_DRIVERS

CONSTANT:
    ``CONFIGURE_APPLICATION_EXTRA_DRIVERS``

DATA TYPE:
    device driver entry structures

RANGE:
    Undefined or set of device driver entry structures

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_APPLICATION_EXTRA_DRIVERS`` is defined if the application has
    device drivers it needs to include in the Device Driver Table.  This should
    be defined to the set of device driver entries that will be placed in the
    table at the *END* of the Device Driver Table.

NOTES:
    None.

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER ===

.. _Enable /dev/null Device Driver:

Enable /dev/null Device Driver
------------------------------
.. index:: CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER
.. index:: /dev/null

CONSTANT:
    ``CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    This configuration variable is specified to enable ``/dev/null`` device driver.

NOTES:
    This device driver is supported by all BSPs.

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER ===

.. _Enable /dev/zero Device Driver:

Enable /dev/zero Device Driver
------------------------------
.. index:: CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER
.. index:: /dev/zero

CONSTANT:
    ``CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    This configuration variable is specified to enable ``/dev/zero`` device driver.

NOTES:
    This device driver is supported by all BSPs.

.. COMMENT: === CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE ===

.. _Specifying Application Defined Device Driver Table:

Specifying Application Defined Device Driver Table
--------------------------------------------------
.. index:: CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE

CONSTANT:
    ``CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default, indicating the ``<rtems/confdefs.h>`` is
    providing the device driver table.

DESCRIPTION:
    ``CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE`` is defined if the application
    wishes to provide their own Device Driver Table.

    The table must be an array of ``rtems_driver_address_table`` entries
    named`` _IO_Driver_address_table``.  The application must also provide a
    const variable ``_IO_Number_of_drivers`` of type ``size_t`` indicating the
    number of entries in the ``_IO_Driver_address_table``.

NOTES:
    It is expected that there the application would only rarely need to do this.

.. COMMENT: === Multiprocessing Configuration ===

Multiprocessing Configuration
=============================

This section defines the multiprocessing related system configuration
parameters supported by ``<rtems/confdefs.h>``.  They are only used if the
Multiprocessing Support (distinct from the SMP support) is enabled at configure
time using the ``--enable-multiprocessing`` option.

Additionally, this class of Configuration Constants are only applicable if
``CONFIGURE_MP_APPLICATION`` is defined.

.. COMMENT: === CONFIGURE_MP_APPLICATION ===

.. _Specify Application Will Use Multiprocessing:

Specify Application Will Use Multiprocessing
--------------------------------------------
.. index:: CONFIGURE_MP_APPLICATION

CONSTANT:
    ``CONFIGURE_MP_APPLICATION``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    This configuration parameter must be defined to indicate that the
    application intends to be part of a multiprocessing
    configuration. Additional configuration parameters are assumed to be
    provided.

NOTES:
    This has no impact unless RTEMS was configured and built using the
    ``--enable-multiprocessing`` option.

.. COMMENT: === CONFIGURE_MP_NODE_NUMBER ===

.. _Configure Node Number in Multiprocessor Configuration:

Configure Node Number in Multiprocessor Configuration
-----------------------------------------------------
.. index:: CONFIGURE_MP_NODE_NUMBER

CONSTANT:
    ``CONFIGURE_MP_NODE_NUMBER``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is ``NODE_NUMBER``, which is assumed to be set by the
    compilation environment.

DESCRIPTION:
    ``CONFIGURE_MP_NODE_NUMBER`` is the node number of this node in a
    multiprocessor system.

NOTES:
    In the RTEMS Multiprocessing Test Suite, the node number is derived from
    the Makefile variable ``NODE_NUMBER``. The same code is compiled with the
    ``NODE_NUMBER`` set to different values. The test programs behave
    differently based upon their node number.

.. COMMENT: === CONFIGURE_MP_MAXIMUM_NODES ===

.. _Configure Maximum Node in Multiprocessor Configuration:

Configure Maximum Node in Multiprocessor Configuration
------------------------------------------------------
.. index:: CONFIGURE_MP_MAXIMUM_NODES

CONSTANT:
    ``CONFIGURE_MP_MAXIMUM_NODES``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is 2.

DESCRIPTION:
    ``CONFIGURE_MP_MAXIMUM_NODES`` is the maximum number of nodes in a
    multiprocessor system.

NOTES:
    None.

.. COMMENT: === CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS ===

.. _Configure Maximum Global Objects in Multiprocessor Configuration:

Configure Maximum Global Objects in Multiprocessor Configuration
----------------------------------------------------------------
.. index:: CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS

CONSTANT:
    ``CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is 32.

DESCRIPTION:
    ``CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS`` is the maximum number of
    concurrently active global objects in a multiprocessor system.

NOTES:
    This value corresponds to the total number of objects which can be created
    with the ``RTEMS_GLOBAL`` attribute.

.. COMMENT: === CONFIGURE_MP_MAXIMUM_PROXIES ===

.. _Configure Maximum Proxies in Multiprocessor Configuration:

Configure Maximum Proxies in Multiprocessor Configuration
---------------------------------------------------------
.. index:: CONFIGURE_MP_MAXIMUM_PROXIES

CONSTANT:
    ``CONFIGURE_MP_MAXIMUM_PROXIES``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Undefined or positive.

DEFAULT VALUE:
    The default value is 32.

DESCRIPTION:
    ``CONFIGURE_MP_MAXIMUM_PROXIES`` is the maximum number of concurrently
    active thread/task proxies on this node in a multiprocessor system.

NOTES:
    Since a proxy is used to represent a remote task/thread which is blocking
    on this node. This configuration parameter reflects the maximum number of
    remote tasks/threads which can be blocked on objects on this node.

.. COMMENT: XXX - add xref to proxy discussion in MP chapter

.. COMMENT: === CONFIGURE_MP_MPCI_TABLE_POINTER ===

.. _Configure MPCI in Multiprocessor Configuration:

Configure MPCI in Multiprocessor Configuration
----------------------------------------------
.. index:: CONFIGURE_MP_MPCI_TABLE_POINTER

CONSTANT:
    ``CONFIGURE_MP_MPCI_TABLE_POINTER``

DATA TYPE:
    pointer to ``rtems_mpci_table``

RANGE:
    undefined or valid pointer

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_MP_MPCI_TABLE_POINTER`` is the pointer to the MPCI
    Configuration Table.  The default value of this field is``&MPCI_table``.

NOTES:
    RTEMS provides a Shared Memory MPCI Device Driver which can be used on any
    Multiprocessor System assuming the BSP provides the proper set of
    supporting methods.

.. COMMENT: === CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE ===

.. _Do Not Generate Multiprocessor Configuration Table:

Do Not Generate Multiprocessor Configuration Table
--------------------------------------------------
.. index:: CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE

CONSTANT:
    ``CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE`` is defined if the application
    wishes to provide their own Multiprocessing Configuration Table.  The
    generated table is named ``Multiprocessing_configuration``.

NOTES:
    This is a configuration parameter which is very unlikely to be used by an
    application. If you find yourself wanting to use it in an application,
    please reconsider and discuss this on the RTEMS Users mailing list.

.. COMMENT: === Ada Tasks ===

Ada Tasks
=========

This section defines the system configuration parameters supported by
``<rtems/confdefs.h>`` related to configuring RTEMS to support a task using Ada
tasking with GNAT/RTEMS.

These configuration parameters are only available when RTEMS is built with the
``--enable-ada`` configure option and the application specifies
``CONFIGURE_GNAT_RTEMS``.

Additionally RTEMS includes an Ada language binding to the Classic API which
has a test suite. This test suite is enabled only when``--enable-tests`` and
``--enable-expada`` are specified on the configure command.

.. COMMENT: === CONFIGURE_GNAT_RTEMS ===

.. _Specify Application Includes Ada Code:

Specify Application Includes Ada Code
-------------------------------------
.. index:: CONFIGURE_GNAT_RTEMS

CONSTANT:
    ``CONFIGURE_GNAT_RTEMS``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_GNAT_RTEMS`` is defined to inform RTEMS that the GNAT Ada
    run-time is to be used by the application.

NOTES:
    This configuration parameter is critical as it makes``<rtems/confdefs.h>``
    configure the resources (POSIX API Threads, Mutexes, Condition Variables,
    and Keys) used implicitly by the GNAT run-time.

.. COMMENT: === CONFIGURE_MAXIMUM_ADA_TASKS ===

.. _Specify the Maximum Number of Ada Tasks.:

Specify the Maximum Number of Ada Tasks.
----------------------------------------
.. index:: CONFIGURE_MAXIMUM_ADA_TASKS

CONSTANT:
    ``CONFIGURE_MAXIMUM_ADA_TASKS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Undefined or positive.

DEFAULT VALUE:
    If ``CONFIGURE_GNAT_RTEMS`` is defined, then the default value is 20,
    otherwise the default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_ADA_TASKS`` is the number of Ada tasks that can be
    concurrently active in the system.

NOTES:
    None.

.. COMMENT: === CONFIGURE_MAXIMUM_FAKE_ADA_TASKS ===

.. _Specify the Maximum Fake Ada Tasks:

Specify the Maximum Fake Ada Tasks
----------------------------------
.. index:: CONFIGURE_MAXIMUM_FAKE_ADA_TASKS

CONSTANT:
    .. index:: ``CONFIGURE_MAXIMUM_FAKE_ADA_TASKS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 0.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_FAKE_ADA_TASKS`` is the number of *fake* Ada tasks that
    can be concurrently active in the system.  A *fake* Ada task is a non-Ada
    task that makes calls back into Ada code and thus implicitly uses the Ada
    run-time.

NOTES:
    None.

.. COMMENT: === PCI Library ===

PCI Library
===========

This section defines the system configuration parameters supported by
``rtems/confdefs.h`` related to configuring the PCI Library for RTEMS.

The PCI Library startup behaviour can be configured in four different ways
depending on how ``CONFIGURE_PCI_CONFIG_LIB`` is defined:

.. index:: PCI_LIB_AUTO

``PCI_LIB_AUTO``
  Used to enable the PCI auto configuration software. PCI will be automatically
  probed, PCI buses enumerated, all devices and bridges will be initialized
  using Plug & Play software routines. The PCI device tree will be populated
  based on the PCI devices found in the system, PCI devices will be configured
  by allocating address region resources automatically in PCI space according
  to the BSP or host bridge driver set up.

.. index:: PCI_LIB_READ

``PCI_LIB_READ``
  Used to enable the PCI read configuration software. The current PCI
  configuration is read to create the RAM representation (the PCI device tree)
  of the PCI devices present. PCI devices are assumed to already have been
  initialized and PCI buses enumerated, it is therefore required that a BIOS or
  a boot loader has set up configuration space prior to booting into RTEMS.

.. index:: PCI_LIB_STATIC

``PCI_LIB_STATIC``
  Used to enable the PCI static configuration software. The user provides a PCI
  tree with information how all PCI devices are to be configured at compile
  time by linking in a custom ``struct pci_bus pci_hb`` tree. The static PCI
  library will not probe PCI for devices, instead it will assume that all
  devices defined by the user are present, it will enumerate the PCI buses and
  configure all PCI devices in static configuration accordingly. Since probe
  and allocation software is not needed the startup is faster, has smaller
  footprint and does not require dynamic memory allocation.

.. index:: PCI_LIB_PERIPHERAL

``PCI_LIB_PERIPHERAL``
  Used to enable the PCI peripheral configuration. It is similar to
  ``PCI_LIB_STATIC``, but it will never write the configuration to the PCI
  devices since PCI peripherals are not allowed to access PCI configuration
  space.

Note that selecting ``PCI_LIB_STATIC`` or ``PCI_LIB_PERIPHERAL`` but not
defining ``pci_hb`` will reuslt in link errors. Note also that in these modes
Plug & Play is not performed.

.. COMMENT: === Go Tasks ===

Go Tasks
========

.. COMMENT: === CONFIGURE_ENABLE_GO ===

.. _Specify Application Includes Go Code:

Specify Application Includes Go Code
------------------------------------
.. index:: CONFIGURE_ENABLE_GO

CONSTANT:
    ``CONFIGURE_ENABLE_GO``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_ENABLE_GO`` is defined to inform RTEMS that the Go run-time is
    to be used by the application.

NOTES:
    The Go language support is experimental

.. COMMENT: === CONFIGURE_MAXIMUM_GOROUTINES ===

.. _Specify the maximum number of Go routines:

Specify the maximum number of Go routines
-----------------------------------------
.. index:: CONFIGURE_MAXIMUM_GOROUTINES

CONSTANT:
    ``CONFIGURE_MAXIMUM_GOROUTINES``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 400

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_GOROUTINES`` is defined to specify the maximum number
    of Go routines.

NOTES:
    The Go language support is experimental

.. COMMENT: === CONFIGURE_MAXIMUM_GO_CHANNELS ===

.. _Specify the maximum number of Go Channels:

Specify the maximum number of Go Channels
-----------------------------------------
.. index:: CONFIGURE_MAXIMUM_GO_CHANNELS

CONSTANT:
    ``CONFIGURE_MAXIMUM_GO_CHANNELS``

DATA TYPE:
    Unsigned integer (``uint32_t``).

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is 500

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_GO_CHANNELS`` is defined to specify the maximum number
    of Go channels.

NOTES:
    The Go language support is experimental

.. COMMENT: === Configuration Data Structures ===

Configuration Data Structures
=============================

It is recommended that applications be configured using ``<rtems/confdefs.h>``
as it is simpler and insulates applications from changes in the underlying data
structures.  However, it is sometimes important to understand the data
structures that are automatically filled in by the configuration parameters.
This section describes the primary configuration data structures.

If the user wishes to see the details of a particular data structure, they are
are advised to look at the source code. After all, that is one of the
advantages of RTEMS.