path: root/c-user/configuring_a_system.rst

.. 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.

.. index:: configuring a system
.. _Configuring a System:

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 must not 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:: <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 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.

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.

.. _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.

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.

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)

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.

.. _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 object classes in the Classic API can be configured in unlimited
mode:

- Barriers

- Message Queues

- Partitions

- Periods

- Ports

- Regions

- Semaphores

- Tasks

- Timers

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

- Keys -- :c:func:`pthread_key_create`

- Key Value Pairs -- :c:func:`pthread_setspecific`

- Message Queues -- :c:func:`mq_open`

- Named Semaphores -- :c:func:`sem_open`

- Shared Memory -- :c:func:`shm_open`

- Threads -- :c:func:`pthread_create`

- Timers -- :c:func:`timer_create`

.. warning::

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

    - Drivers

    - File Descriptors

    - POSIX Queued Signals

    - User Extensions

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.

.. _Per Object Class Unlimited Object Instances:

.. index:: rtems_resource_unlimited

Per Object Class Unlimited Object Instances
-------------------------------------------

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.

.. _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.

.. index:: CONFIGURE_UNLIMITED_OBJECTS

.. _CONFIGURE_UNLIMITED_OBJECTS:

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.

.. _CONFIGURE_UNLIMITED_ALLOCATION_SIZE:

CONFIGURE_UNLIMITED_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

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

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

.. index:: CONFIGURE_MAXIMUM_TASKS

.. _CONFIGURE_MAXIMUM_TASKS:

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
    :ref:`CONFIGURE_MAXIMUM_POSIX_THREADS <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.

.. index:: CONFIGURE_MAXIMUM_TIMERS

.. _CONFIGURE_MAXIMUM_TIMERS:

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.

.. index:: CONFIGURE_MAXIMUM_SEMAPHORES

.. _CONFIGURE_MAXIMUM_SEMAPHORES:

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.

.. index:: CONFIGURE_MAXIMUM_MRSP_SEMAPHORES

.. _CONFIGURE_MAXIMUM_MRSP_SEMAPHORES:

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 :ref:`MrsP` that can be concurrently active.

NOTES:
    This configuration option is only used in SMP configurations.  In
    uniprocessor configurations, the :ref:`PriorityCeiling` is used for MrsP
    semaphores and thus no extra memory is necessary.

.. index:: CONFIGURE_MAXIMUM_MESSAGE_QUEUES

.. _CONFIGURE_MAXIMUM_MESSAGE_QUEUES:

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.

.. index:: CONFIGURE_MAXIMUM_BARRIERS

.. _CONFIGURE_MAXIMUM_BARRIERS:

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.

.. index:: CONFIGURE_MAXIMUM_PERIODS

.. _CONFIGURE_MAXIMUM_PERIODS:

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.

.. index:: CONFIGURE_MAXIMUM_PARTITIONS

.. _CONFIGURE_MAXIMUM_PARTITIONS:

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.

.. index:: CONFIGURE_MAXIMUM_REGIONS

.. _CONFIGURE_MAXIMUM_REGIONS:

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.

.. index:: CONFIGURE_MAXIMUM_PORTS

.. _CONFIGURE_MAXIMUM_PORTS:

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.

.. index:: CONFIGURE_MAXIMUM_USER_EXTENSIONS

.. _CONFIGURE_MAXIMUM_USER_EXTENSIONS:

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.

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.

.. index:: CONFIGURE_RTEMS_INIT_TASKS_TABLE

.. _CONFIGURE_RTEMS_INIT_TASKS_TABLE:

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.

.. index:: CONFIGURE_INIT_TASK_ENTRY_POINT

.. _CONFIGURE_INIT_TASK_ENTRY_POINT:

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.

.. index:: CONFIGURE_INIT_TASK_NAME

.. _CONFIGURE_INIT_TASK_NAME:

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.

.. index:: CONFIGURE_INIT_TASK_STACK_SIZE

.. _CONFIGURE_INIT_TASK_STACK_SIZE:

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``.

.. index:: CONFIGURE_INIT_TASK_PRIORITY

.. _CONFIGURE_INIT_TASK_PRIORITY:

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.


.. index:: CONFIGURE_INIT_TASK_ATTRIBUTES

.. _CONFIGURE_INIT_TASK_ATTRIBUTES:

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.

.. index:: CONFIGURE_INIT_TASK_INITIAL_MODES

.. _CONFIGURE_INIT_TASK_INITIAL_MODES:

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.

.. index:: CONFIGURE_INIT_TASK_ARGUMENTS

.. _CONFIGURE_INIT_TASK_ARGUMENTS:

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.

.. index:: CONFIGURE_HAS_OWN_INIT_TASK_TABLE

.. _CONFIGURE_HAS_OWN_INIT_TASK_TABLE:

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.

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

The parameters in this section are used to configure resources for the POSIX
API supported by RTEMS.  Most POSIX API objects are available by default since
RTEMS 5.1.  The queued signals and timers are only available if RTEMS was built
with the ``--enable-posix`` build configuration option.

.. index:: CONFIGURE_MAXIMUM_POSIX_KEYS

.. _CONFIGURE_MAXIMUM_POSIX_KEYS:

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.

.. index:: CONFIGURE_MAXIMUM_POSIX_KEY_VALUE_PAIRS

.. _CONFIGURE_MAXIMUM_POSIX_KEY_VALUE_PAIRS

CONFIGURE_MAXIMUM_POSIX_KEY_VALUE_PAIRS
---------------------------------------

CONSTANT:
    ``CONFIGURE_MAXIMUM_POSIX_KEY_VALUE_PAIRS``

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

RANGE:
    Zero or positive.

DEFAULT VALUE:
    The default value is
    :ref:`CONFIGURE_MAXIMUM_POSIX_KEYS <CONFIGURE_MAXIMUM_POSIX_KEYS>` *
    :ref:`CONFIGURE_MAXIMUM_TASKS <CONFIGURE_MAXIMUM_TASKS>` +
    :ref:`CONFIGURE_MAXIMUM_POSIX_THREADS <CONFIGURE_MAXIMUM_POSIX_THREADS>`.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_POSIX_KEY_VALUE_PAIRS`` is the maximum number of key
    value pairs used by POSIX API Keys that can be concurrently active.

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

    A key value pair is created by :c:func:`pthread_setspecific` if the value
    is not :c:macro:`NULL`, otherwise it is deleted.

.. index:: CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES

.. _CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES:

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.

.. index:: CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS

.. _CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS:

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:
    Unlimited objects are not available for queued signals.

    Queued signals are only available if RTEMS was built with the
    ``--enable-posix`` build configuration option.

.. index:: CONFIGURE_MAXIMUM_POSIX_SEMAPHORES

.. _CONFIGURE_MAXIMUM_POSIX_SEMAPHORES:

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
    Named Semaphores that can be concurrently active.

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

    Named semaphores are created with ``sem_open()``.  Semaphores initialized
    with ``sem_init()`` are not affected by this configuration option since the
    storage space for these semaphores is user-provided.

.. index:: CONFIGURE_MAXIMUM_POSIX_TIMERS

.. _CONFIGURE_MAXIMUM_POSIX_TIMERS:

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.

    Timers are only available if RTEMS was built with the
    ``--enable-posix`` build configuration option.

.. index:: CONFIGURE_MAXIMUM_POSIX_THREADS

.. _CONFIGURE_MAXIMUM_POSIX_THREADS:

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
    :ref:`CONFIGURE_MAXIMUM_TASKS <CONFIGURE_MAXIMUM_TASKS>`.

    All POSIX threads have floating point enabled.

.. index:: CONFIGURE_MINIMUM_POSIX_THREAD_STACK_SIZE
.. index:: minimum POSIX thread stack size

.. _CONFIGURE_MINIMUM_POSIX_THREAD_STACK_SIZE:

CONFIGURE_MINIMUM_POSIX_THREAD_STACK_SIZE
-----------------------------------------

CONSTANT:
    ``CONFIGURE_MINIMUM_POSIX_THREAD_STACK_SIZE``

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

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is two times the value of
    :ref:`CONFIGURE_MINIMUM_TASK_STACK_SIZE <CONFIGURE_MINIMUM_TASK_STACK_SIZE>`.

DESCRIPTION:
    This configuration parameter defines the minimum stack size in bytes for
    every POSIX thread in the system.

NOTES:
    None.

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.

.. index:: CONFIGURE_POSIX_INIT_THREAD_TABLE

.. _CONFIGURE_POSIX_INIT_THREAD_TABLE:

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.

.. index:: CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT

.. _CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT:

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.

.. index:: CONFIGURE_POSIX_INIT_THREAD_STACK_SIZE

.. _CONFIGURE_POSIX_INIT_THREAD_STACK_SIZE:

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``.

.. index:: CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE

.. _CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE:

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.

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

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

.. index:: CONFIGURE_UNIFIED_WORK_AREAS
.. index:: unified work areas
.. index:: separate work areas
.. index:: RTEMS Workspace
.. index:: C Program Heap

.. _CONFIGURE_UNIFIED_WORK_AREAS:

CONFIGURE_UNIFIED_WORK_AREAS
----------------------------

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.

.. index:: CONFIGURE_MAXIMUM_PROCESSORS

.. _CONFIGURE_MAXIMUM_PROCESSORS:

CONFIGURE_MAXIMUM_PROCESSORS
----------------------------

CONSTANT:
    ``CONFIGURE_MAXIMUM_PROCESSORS``

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

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is 1.

DESCRIPTION:
    ``CONFIGURE_MAXIMUM_PROCESSORS`` must be set to the maximum number of
    processors an application intends to use.  The number of actually available
    processors depends on the hardware and may be less.  It is recommended to
    use the smallest value suitable for the application in order to save
    memory.  Each processor needs an idle thread and interrupt stack for
    example.

NOTES:
    If there are more processors available than configured, the rest will be
    ignored.  This configuration define is ignored in uniprocessor
    configurations.

.. index:: CONFIGURE_MICROSECONDS_PER_TICK
.. index:: tick quantum

.. _CONFIGURE_MICROSECONDS_PER_TICK:

CONFIGURE_MICROSECONDS_PER_TICK
-------------------------------

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.

.. index:: CONFIGURE_TICKS_PER_TIMESLICE
.. index:: ticks per timeslice

.. _CONFIGURE_TICKS_PER_TIMESLICE:

CONFIGURE_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.

.. index:: CONFIGURE_MAXIMUM_PRIORITY
.. index:: maximum priority
.. index:: number of priority levels

.. _CONFIGURE_MAXIMUM_PRIORITY:

CONFIGURE_MAXIMUM_PRIORITY
--------------------------

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.

.. index:: CONFIGURE_MAXIMUM_THREAD_NAME_SIZE
.. index:: maximum thread name size

.. _CONFIGURE_MAXIMUM_THREAD_NAME_SIZE:

CONFIGURE_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 5.1.

.. index:: CONFIGURE_MINIMUM_TASK_STACK_SIZE
.. index:: minimum task stack size

.. _CONFIGURE_MINIMUM_TASK_STACK_SIZE:

CONFIGURE_MINIMUM_TASK_STACK_SIZE
---------------------------------

CONSTANT:
    ``CONFIGURE_MINIMUM_TASK_STACK_SIZE``

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

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is architecture-specific.

DESCRIPTION:
    This configuration parameter defines the minimum stack size in bytes for
    every user task or thread in the system.

NOTES:
    Adjusting this parameter should be done with caution.  Examining the actual
    stack usage using the stack checker usage reporting facility is recommended
    (see also :ref:`CONFIGURE_STACK_CHECKER_ENABLED <CONFIGURE_STACK_CHECKER_ENABLED>`).

    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.

    By default, this configuration parameter defines also the minimum stack
    size of POSIX threads.  This can be changed with the
    :ref:`CONFIGURE_MINIMUM_POSIX_THREAD_STACK_SIZE <CONFIGURE_MINIMUM_POSIX_THREAD_STACK_SIZE>`
    configuration option.

    In releases before RTEMS 5.1 the ``CONFIGURE_MINIMUM_TASK_STACK_SIZE`` was
    used to define the default value of :ref:`CONFIGURE_INTERRUPT_STACK_SIZE
    <CONFIGURE_INTERRUPT_STACK_SIZE>`.

.. index:: CONFIGURE_INTERRUPT_STACK_SIZE
.. index:: interrupt stack size

.. _CONFIGURE_INTERRUPT_STACK_SIZE:

CONFIGURE_INTERRUPT_STACK_SIZE
------------------------------

CONSTANT:
    ``CONFIGURE_INTERRUPT_STACK_SIZE``

DATA TYPE:
    Unsigned integer.

RANGE:
    Positive.

DEFAULT VALUE:
    The default value is ``BSP_INTERRUPT_STACK_SIZE`` in case it is defined,
    otherwise the default value is ``CPU_STACK_MINIMUM_SIZE``.

DESCRIPTION:
    The ``CONFIGURE_INTERRUPT_STACK_SIZE`` configuration option defines the
    size of an interrupt stack in bytes.

NOTES:
    The interrupt stack size must be aligned according to
    ``CPU_INTERRUPT_STACK_ALIGNMENT``.

    There is one interrupt stack available for each configured processor
    (:ref:`CONFIGURE_MAXIMUM_PROCESSORS <CONFIGURE_MAXIMUM_PROCESSORS>`).  The
    interrupt stack areas are statically allocated in a special linker section
    (``.rtemsstack.interrupt``).  The placement of this linker section is
    BSP-specific.

    Some BSPs use the interrupt stack as the initialization stack which is used
    to perform the sequential system initialization before the multithreading
    is started.

    The interrupt stacks are covered by the :ref:`stack checker
    <CONFIGURE_STACK_CHECKER_ENABLED>`.  However, using a too small interrupt
    stack size may still result in undefined behaviour.

    In releases before RTEMS 5.1 the default value was
    :ref:`CONFIGURE_MINIMUM_TASK_STACK_SIZE
    <CONFIGURE_MINIMUM_TASK_STACK_SIZE>` instead of ``CPU_STACK_MINIMUM_SIZE``.

.. index:: CONFIGURE_EXTRA_TASK_STACKS
.. index:: memory for task tasks

.. _CONFIGURE_EXTRA_TASK_STACKS:

CONFIGURE_EXTRA_TASK_STACKS
---------------------------

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>``.

.. index:: CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY
.. index:: clear C Program Heap
.. index:: clear RTEMS Workspace
.. index:: zero C Program Heap
.. index:: zero RTEMS Workspace

.. _CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY:

CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY
--------------------------------------

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.

.. index:: CONFIGURE_STACK_CHECKER_ENABLED

.. _CONFIGURE_STACK_CHECKER_ENABLED:

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.

.. index:: CONFIGURE_INITIAL_EXTENSIONS

.. _CONFIGURE_INITIAL_EXTENSIONS:

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.

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.

.. index:: CONFIGURE_TASK_STACK_ALLOCATOR_INIT

.. _CONFIGURE_TASK_STACK_ALLOCATOR_INIT:

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``

.. index:: CONFIGURE_TASK_STACK_ALLOCATOR
.. index:: task stack allocator

.. _CONFIGURE_TASK_STACK_ALLOCATOR:

CONFIGURE_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``

.. index:: CONFIGURE_TASK_STACK_DEALLOCATOR
.. index:: task stack deallocator

.. _CONFIGURE_TASK_STACK_DEALLOCATOR:

CONFIGURE_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``

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.

.. index:: CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE
.. index:: memory for a single message queue's buffers

.. _CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE:

CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE
-----------------------------------

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``.

.. index:: CONFIGURE_MESSAGE_BUFFER_MEMORY
.. index:: configure message queue buffer memory

.. _CONFIGURE_MESSAGE_BUFFER_MEMORY:

CONFIGURE_MESSAGE_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) \
                     )

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.

.. index:: CONFIGURE_MEMORY_OVERHEAD

.. _CONFIGURE_MEMORY_OVERHEAD:

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.

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

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

.. index:: CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS
.. index:: maximum file descriptors

.. _CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS:

CONFIGURE_LIBIO_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.

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

This section defines File System related configuration parameters.

.. index:: CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM

.. _CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM:

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.

.. index:: CONFIGURE_MAXIMUM_DEVICES

.. _CONFIGURE_MAXIMUM_DEVICES:

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.

.. index:: CONFIGURE_APPLICATION_DISABLE_FILESYSTEM

.. _CONFIGURE_APPLICATION_DISABLE_FILESYSTEM:

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.

.. index:: CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM

.. _CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM:

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``.

.. index:: CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK

.. _CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK:

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.

.. index:: CONFIGURE_IMFS_DISABLE_CHOWN

.. _CONFIGURE_IMFS_DISABLE_CHOWN:

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.

.. index:: CONFIGURE_IMFS_DISABLE_CHMOD

.. _CONFIGURE_IMFS_DISABLE_CHMOD:

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.

.. index:: CONFIGURE_IMFS_DISABLE_UTIME

.. _CONFIGURE_IMFS_DISABLE_UTIME:

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.

.. index:: CONFIGURE_IMFS_DISABLE_LINK

.. _CONFIGURE_IMFS_DISABLE_LINK:

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.

.. index:: CONFIGURE_IMFS_DISABLE_SYMLINK

.. _CONFIGURE_IMFS_DISABLE_SYMLINK:

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.

.. index:: CONFIGURE_IMFS_DISABLE_READLINK

.. _CONFIGURE_IMFS_DISABLE_READLINK:

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.

.. index:: CONFIGURE_IMFS_DISABLE_RENAME

.. _CONFIGURE_IMFS_DISABLE_RENAME:

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.

.. index:: CONFIGURE_IMFS_DISABLE_READDIR

.. _CONFIGURE_IMFS_DISABLE_READDIR:

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.

.. index:: CONFIGURE_IMFS_DISABLE_MOUNT

.. _CONFIGURE_IMFS_DISABLE_MOUNT:

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.

.. index:: CONFIGURE_IMFS_DISABLE_UNMOUNT

.. _CONFIGURE_IMFS_DISABLE_UNMOUNT:

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.

.. index:: CONFIGURE_IMFS_DISABLE_MKNOD

.. _CONFIGURE_IMFS_DISABLE_MKNOD:

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.

.. index:: CONFIGURE_IMFS_DISABLE_MKNOD_FILE

.. _CONFIGURE_IMFS_DISABLE_MKNOD_FILE:

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.

.. index:: CONFIGURE_IMFS_DISABLE_RMNOD

.. _CONFIGURE_IMFS_DISABLE_RMNOD:

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.

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

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

.. index:: CONFIGURE_APPLICATION_NEEDS_LIBBLOCK

.. _CONFIGURE_APPLICATION_NEEDS_LIBBLOCK:

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.

.. index:: CONFIGURE_BDBUF_CACHE_MEMORY_SIZE

.. _CONFIGURE_BDBUF_CACHE_MEMORY_SIZE:

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.

.. index:: CONFIGURE_BDBUF_BUFFER_MIN_SIZE

.. _CONFIGURE_BDBUF_BUFFER_MIN_SIZE:

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.

.. index:: CONFIGURE_BDBUF_BUFFER_MAX_SIZE

.. _CONFIGURE_BDBUF_BUFFER_MAX_SIZE:

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.

.. index:: CONFIGURE_SWAPOUT_SWAP_PERIOD

.. _CONFIGURE_SWAPOUT_SWAP_PERIOD:

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.

.. index:: CONFIGURE_SWAPOUT_BLOCK_HOLD

.. _CONFIGURE_SWAPOUT_BLOCK_HOLD:

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.

.. index:: CONFIGURE_SWAPOUT_TASK_PRIORITY

.. _CONFIGURE_SWAPOUT_TASK_PRIORITY:

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.

.. index:: CONFIGURE_BDBUF_MAX_READ_AHEAD_BLOCKS

.. _CONFIGURE_BDBUF_MAX_READ_AHEAD_BLOCKS:

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.

.. index:: CONFIGURE_BDBUF_MAX_WRITE_BLOCKS

.. _CONFIGURE_BDBUF_MAX_WRITE_BLOCKS:

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.

.. index:: CONFIGURE_BDBUF_TASK_STACK_SIZE

.. _CONFIGURE_BDBUF_TASK_STACK_SIZE:

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.

.. index:: CONFIGURE_BDBUF_READ_AHEAD_TASK_PRIORITY

.. _CONFIGURE_BDBUF_READ_AHEAD_TASK_PRIORITY:

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.

.. index:: CONFIGURE_SWAPOUT_WORKER_TASKS

.. _CONFIGURE_SWAPOUT_WORKER_TASKS:

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.

.. index:: CONFIGURE_SWAPOUT_WORKER_TASK_PRIORITY

.. _CONFIGURE_SWAPOUT_WORKER_TASK_PRIORITY:

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.

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>``.

.. index:: CONFIGURE_DISABLE_BSP_SETTINGS

.. _CONFIGURE_DISABLE_BSP_SETTINGS:

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.

.. index:: CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK

.. _CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK:

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.

.. index:: BSP_IDLE_TASK_BODY

.. _BSP_IDLE_TASK_BODY:

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

.. index:: BSP_IDLE_TASK_STACK_SIZE

.. _BSP_IDLE_TASK_STACK_SIZE:

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.

.. index:: BSP_INITIAL_EXTENSION

.. _BSP_INITIAL_EXTENSION:

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.

.. index:: BSP_INTERRUPT_STACK_SIZE

.. _BSP_INTERRUPT_STACK_SIZE:

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.

.. index:: BSP_MAXIMUM_DEVICES

.. _BSP_MAXIMUM_DEVICES:

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.

.. index:: BSP_ZERO_WORKSPACE_AUTOMATICALLY

.. _BSP_ZERO_WORKSPACE_AUTOMATICALLY:

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.

.. index:: CONFIGURE_BSP_PREREQUISITE_DRIVERS

.. _CONFIGURE_BSP_PREREQUISITE_DRIVERS:

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.

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

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

.. index:: CONFIGURE_IDLE_TASK_BODY

.. _CONFIGURE_IDLE_TASK_BODY:

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.

.. index:: CONFIGURE_IDLE_TASK_STACK_SIZE

.. _CONFIGURE_IDLE_TASK_STACK_SIZE:

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.

.. index:: CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION

.. _CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION:

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.

General Scheduler Configuration
===============================

This section defines the configuration parameters related to selecting a
scheduling algorithm for an application.  A scheduler configuration is optional
and only necessary in very specific circumstances.  A normal application
configuration does not need any of the configuration options described in this
section.  By default, the :ref:`Deterministic Priority Scheduler
<SchedulerPriority>` algorithm is used in uniprocessor configurations.  In case
SMP is enabled and the configured maximum processors
(:ref:`CONFIGURE_MAXIMUM_PROCESSORS <CONFIGURE_MAXIMUM_PROCESSORS>`) is greater
than one, then the :ref:`Earliest Deadline First (EDF) SMP Scheduler
<SchedulerSMPEDF>` is selected as the default scheduler algorithm.

For the :ref:`schedulers built into
RTEMS <SchedulingConcepts>`, 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 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.

.. index:: CONFIGURE_SCHEDULER_CBS

.. _CONFIGURE_SCHEDULER_CBS:

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:
    If defined, then the :ref:`Constant Bandwidth Server (CBS) Scheduler
    <SchedulerCBS>` algorithm is made available to the application.

NOTES:
    This scheduler configuration option is an advanced configuration option.
    Think twice before you use it.

    In case no explicit :ref:`clustered scheduler configuration
    <ConfigurationSchedulersClustered>` is present, then it is used as the
    scheduler for exactly one processor.

.. index:: CONFIGURE_SCHEDULER_EDF

.. _CONFIGURE_SCHEDULER_EDF:

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:
    If defined, then the :ref:`Earliest Deadline First (EDF) Scheduler
    <SchedulerEDF>` algorithm is made available to the application.

NOTES:
    This scheduler configuration option is an advanced configuration option.
    Think twice before you use it.

    In case no explicit :ref:`clustered scheduler configuration
    <ConfigurationSchedulersClustered>` is present, then it is used as the
    scheduler for exactly one processor.

.. index:: CONFIGURE_SCHEDULER_EDF_SMP

.. _CONFIGURE_SCHEDULER_EDF_SMP:

CONFIGURE_SCHEDULER_EDF_SMP
---------------------------

CONSTANT:
    ``CONFIGURE_SCHEDULER_EDF_SMP``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    If defined, then the :ref:`Earliest Deadline First (EDF) SMP Scheduler
    <SchedulerSMPEDF>` algorithm is made available to the application.

NOTES:
    This scheduler configuration option is an advanced configuration option.
    Think twice before you use it.

    This scheduler algorithm is only available when RTEMS is built with SMP
    support enabled.

    In case no explicit :ref:`clustered scheduler configuration
    <ConfigurationSchedulersClustered>` is present, then it is used as the
    scheduler for up to 32 processors.

    This scheduler algorithm is the default in SMP configurations if
    :ref:`CONFIGURE_MAXIMUM_PROCESSORS <CONFIGURE_MAXIMUM_PROCESSORS>` is
    greater than one.

.. index:: CONFIGURE_SCHEDULER_NAME

.. _CONFIGURE_SCHEDULER_NAME:

CONFIGURE_SCHEDULER_NAME
------------------------

CONSTANT:
    ``CONFIGURE_SCHEDULER_NAME``

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

RANGE:
    Any value.

DEFAULT VALUE:
    The default name is

      - ``"MEDF"`` for the :ref:`EDF SMP Scheduler <SchedulerSMPEDF>`,
      - ``"MPA "`` for the :ref:`Arbitrary Processor Affinity Priority SMP Scheduler <SchedulerSMPPriorityAffinity>`,
      - ``"MPD "`` for the :ref:`Deterministic Priority SMP Scheduler <SchedulerSMPPriority>`,
      - ``"MPS "`` for the :ref:`Simple Priority SMP Scheduler <SchedulerSMPPrioritySimple>`,
      - ``"UCBS"`` for the :ref:`Uniprocessor CBS Scheduler <SchedulerCBS>`,
      - ``"UEDF"`` for the :ref:`Uniprocessor EDF Scheduler <SchedulerEDF>`,
      - ``"UPD "`` for the :ref:`Uniprocessor Deterministic Priority Scheduler <SchedulerPriority>`, and
      - ``"UPS "`` for the :ref:`Uniprocessor Simple Priority Scheduler <SchedulerPrioritySimple>`.

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

NOTES:
    This scheduler configuration option is an advanced configuration option.
    Think twice before you use it.

.. index:: CONFIGURE_SCHEDULER_PRIORITY

.. _CONFIGURE_SCHEDULER_PRIORITY:

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:
    If defined, then the :ref:`Deterministic Priority Scheduler
    <SchedulerPriority>` algorithm is made available to the application.

NOTES:
    This scheduler configuration option is an advanced configuration option.
    Think twice before you use it.

    In case no explicit :ref:`clustered scheduler configuration
    <ConfigurationSchedulersClustered>` is present, then it is used as the
    scheduler for exactly one processor.

    This scheduler algorithm is the default when
    :ref:`CONFIGURE_MAXIMUM_PROCESSORS <CONFIGURE_MAXIMUM_PROCESSORS>` is
    exactly one.

.. index:: CONFIGURE_SCHEDULER_PRIORITY_AFFINITY_SMP

.. _CONFIGURE_SCHEDULER_PRIORITY_AFFINITY_SMP:

CONFIGURE_SCHEDULER_PRIORITY_AFFINITY_SMP
-----------------------------------------

CONSTANT:
    ``CONFIGURE_SCHEDULER_PRIORITY_AFFINITY_SMP``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    If defined, then the :ref:`Arbitrary Processor Affinity SMP Scheduler
    <SchedulerSMPPriorityAffinity>` algorithm is made available to the
    application.

NOTES:
    This scheduler configuration option is an advanced configuration option.
    Think twice before you use it.

    This scheduler algorithm is only available when RTEMS is built with SMP
    support enabled.

    In case no explicit :ref:`clustered scheduler configuration
    <ConfigurationSchedulersClustered>` is present, then it is used as the
    scheduler for up to 32 processors.

.. index:: CONFIGURE_SCHEDULER_PRIORITY_SMP

.. _CONFIGURE_SCHEDULER_PRIORITY_SMP:

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:
    If defined, then the :ref:`Deterministic Priority SMP Scheduler
    <SchedulerSMPPriority>` algorithm is made available to the application.

NOTES:
    This scheduler configuration option is an advanced configuration option.
    Think twice before you use it.

    This scheduler algorithm is only available when RTEMS is built with SMP
    support enabled.

    In case no explicit :ref:`clustered scheduler configuration
    <ConfigurationSchedulersClustered>` is present, then it is used as the
    scheduler for up to 32 processors.

.. index:: CONFIGURE_SCHEDULER_SIMPLE

.. _CONFIGURE_SCHEDULER_SIMPLE:

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:
    If defined, then the :ref:`Simple Priority Scheduler
    <SchedulerPrioritySimple>` algorithm is made available to the application.

NOTES:
    This scheduler configuration option is an advanced configuration option.
    Think twice before you use it.

    In case no explicit :ref:`clustered scheduler configuration
    <ConfigurationSchedulersClustered>` is present, then it is used as the
    scheduler for exactly one processor.

.. index:: CONFIGURE_SCHEDULER_SIMPLE_SMP

.. _CONFIGURE_SCHEDULER_SIMPLE_SMP:

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:
    If defined, then the :ref:`Simple Priority SMP Scheduler
    <SchedulerSMPPrioritySimple>` algorithm is made available to the
    application.

NOTES:
    This scheduler configuration option is an advanced configuration option.
    Think twice before you use it.

    This scheduler algorithm is only available when RTEMS is built with SMP
    support enabled.

    In case no explicit :ref:`clustered scheduler configuration
    <ConfigurationSchedulersClustered>` is present, then it is used as the
    scheduler for up to 32 processors.

.. index:: CONFIGURE_SCHEDULER_USER

.. _CONFIGURE_SCHEDULER_USER:

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`` must be defined to a static definition of
      the scheduler data structures of the user scheduler.

    - ``CONFIGURE_SCHEDULER_TABLE_ENTRIES`` must be defined to a scheduler
      table entry 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:
    This scheduler configuration option is an advanced configuration option.
    Think twice before you use it.

    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.

.. _ConfigurationSchedulersClustered:

Clustered Scheduler Configuration
=================================

A clustered scheduler configuration is optional.  It is an advanced
configuration area and only necessary in specific circumstances.

Clustered scheduling helps to control the worst-case latencies in a
multiprocessor system (SMP).  The goal is to reduce the amount of shared state
in the system and thus prevention of lock contention.  Modern multiprocessor
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.

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 algorithm is used for which cluster?

The schedulers are statically configured.

Configuration Step 1 - Scheduler Algorithms
-------------------------------------------

Firstly, the application must select which scheduling algorithms are available
with the following defines

- :ref:`CONFIGURE_SCHEDULER_EDF_SMP <CONFIGURE_SCHEDULER_EDF_SMP>`,

- :ref:`CONFIGURE_SCHEDULER_PRIORITY_AFFINITY_SMP <CONFIGURE_SCHEDULER_PRIORITY_AFFINITY_SMP>`,

- :ref:`CONFIGURE_SCHEDULER_PRIORITY_SMP <CONFIGURE_SCHEDULER_PRIORITY_SMP>`, and

- :ref:`CONFIGURE_SCHEDULER_SIMPLE_SMP <CONFIGURE_SCHEDULER_SIMPLE_SMP>`.

This is necessary to calculate the per-thread overhead introduced by the
scheduler algorithms.  After these definitions the configuration file must
``#include <rtems/scheduler.h>`` to have access to scheduler-specific
configuration macros.

It is possible to make more than one scheduler algorithm available to the
application.  For example a :ref:`Simple Priority SMP Scheduler
<SchedulerSMPPrioritySimple>` could be used in a partition for low latency
tasks in addition to an :ref:`EDF SMP Scheduler <SchedulerSMPEDF>` for a
general-purpose cluster.  Since the per-thread overhead depends on the
scheduler algorithm only the scheduler algorithms used by the application
should be configured.

Configuration Step 2 - Schedulers
---------------------------------

Each scheduler needs some data structures.  Use the following macros to create
the scheduler data structures for a particular scheduler identified in the
configuration by ``name``.

- ``RTEMS_SCHEDULER_EDF_SMP(name, max_cpu_count)``,

- ``RTEMS_SCHEDULER_PRIORITY_AFFINITY_SMP(name, prio_count)``,

- ``RTEMS_SCHEDULER_PRIORITY_SMP(name, prio_count)``, and

- ``RTEMS_SCHEDULER_SIMPLE_SMP(name)``.

The ``name`` parameter is used as part of a designator for scheduler-specific
data structures, so the usual C/C++ designator rules apply.  This ``name`` is
not the scheduler object name.  Additional parameters are scheduler-specific.

.. _ConfigurationSchedulerTable:

Configuration Step 3 - Scheduler Table
--------------------------------------

The schedulers are registered in the system via the scheduler table.  To
populate the scheduler table define ``CONFIGURE_SCHEDULER_TABLE_ENTRIES`` to a
list of the following scheduler table entry initializers

- ``RTEMS_SCHEDULER_TABLE_EDF_SMP(name, obj_name)``,

- ``RTEMS_SCHEDULER_TABLE_PRIORITY_AFFINITY_SMP(name, obj_name)``,

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

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

The ``name`` parameter must correspond to the parameter defining the scheduler
data structures of configuration step 2.  The ``obj_name`` determines the
scheduler object name and can be used in :ref:`rtems_scheduler_ident()
<rtems_scheduler_ident>` to get the scheduler object identifier.  The scheduler
index is defined by the index of the scheduler table.  It is a configuration
error to add a scheduler multiple times to the scheduler table.

Configuration Step 4 - Processor to Scheduler Assignment
--------------------------------------------------------

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
(:ref:`CONFIGURE_MAXIMUM_PROCESSORS <CONFIGURE_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_SCHEDULER_ASSIGNMENTS`` to a list of

- ``RTEMS_SCHEDULER_ASSIGN(scheduler_index, attr)`` and

- ``RTEMS_SCHEDULER_ASSIGN_NO_SCHEDULER``

macros.  The ``scheduler_index`` parameter must be a valid index into the
scheduler table defined by configuration step 3.  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 schedulers at run-time, see
:ref:`rtems_scheduler_add_processor() <rtems_scheduler_add_processor>` and
:ref:`rtems_scheduler_remove_processor() <rtems_scheduler_remove_processor>`.

Configuration 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 SMP schedulers
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_MAXIMUM_PROCESSORS 8
    #define CONFIGURE_MAXIMUM_PRIORITY 255

    /* Configuration Step 1 - Scheduler Algorithms */
    #define CONFIGURE_SCHEDULER_PRIORITY_SMP
    #include <rtems/scheduler.h>

    /* Configuration Step 2 - Schedulers */
    RTEMS_SCHEDULER_PRIORITY_SMP(io, CONFIGURE_MAXIMUM_PRIORITY + 1);
    RTEMS_SCHEDULER_PRIORITY_SMP(work, CONFIGURE_MAXIMUM_PRIORITY + 1);

    /* Configuration Step 3 - Scheduler Table */
    #define CONFIGURE_SCHEDULER_TABLE_ENTRIES \\
      RTEMS_SCHEDULER_TABLE_PRIORITY_SMP( \
        io, \
         rtems_build_name('I', 'O', ' ', ' ') \
      ), \
      RTEMS_SCHEDULER_TABLE_PRIORITY_SMP( \
        work, \
        rtems_build_name('W', 'O', 'R', 'K') \
      )

    /* Configuration Step 4 - Processor to Scheduler Assignment */
    #define CONFIGURE_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)

Configuration Errors
--------------------

In case one of the scheduler indices in ``CONFIGURE_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``.

- ``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_SCHEDULER_ASSIGNMENTS`` definition.

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

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.

.. index:: CONFIGURE_MAXIMUM_DRIVERS

.. _CONFIGURE_MAXIMUM_DRIVERS:

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.

.. index:: CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER

.. _CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER:

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 the :file:`/dev/console`
    device file.  This device is used to initialize the standard input, output,
    and error file descriptors.

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

    The

    * ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER``,

    * ``CONFIGURE_APPLICATION_NEEDS_SIMPLE_CONSOLE_DRIVER``, and

    * ``CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER``

    configuration options are mutually exclusive.

.. index:: CONFIGURE_APPLICATION_NEEDS_SIMPLE_CONSOLE_DRIVER

.. _CONFIGURE_APPLICATION_NEEDS_SIMPLE_CONSOLE_DRIVER:

CONFIGURE_APPLICATION_NEEDS_SIMPLE_CONSOLE_DRIVER
-------------------------------------------------

CONSTANT:
    ``CONFIGURE_APPLICATION_NEEDS_SIMPLE_CONSOLE_DRIVER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

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

NOTES:
    This device driver is responsible for providing the :file:`/dev/console`
    device file.  This device is used to initialize the standard input, output,
    and error file descriptors.

    This device driver reads via ``getchark()``.

    This device driver writes via ``rtems_putc()``.

    The Termios framework is not used.  There is no support to change device
    settings, e.g. baud, stop bits, parity, etc.

    The

    * ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER``,

    * ``CONFIGURE_APPLICATION_NEEDS_SIMPLE_CONSOLE_DRIVER``, and

    * ``CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER``

    configuration options are mutually exclusive.

.. index:: CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER

.. _CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER:

CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER
------------------------------------------------------

CONSTANT:
    ``CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER``

DATA TYPE:
    Boolean feature macro.

RANGE:
    Defined or undefined.

DEFAULT VALUE:
    This is not defined by default.

DESCRIPTION:
    ``CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER`` is defined if
    the application wishes to include the Simple Task Console Device Driver.

NOTES:
    This device driver is responsible for providing the :file:`/dev/console`
    device file.  This device is used to initialize the standard input, output,
    and error file descriptors.

    This device driver reads via ``getchark()``.

    This device driver writes into a write buffer.  The count of characters
    written into the write buffer is returned.  It might be less than the
    requested count, in case the write buffer is full.  The write is
    non-blocking and may be called from interrupt context.  A dedicated task
    reads from the write buffer and outputs the characters via
    ``rtems_putc()``.  This task runs with the least important priority.  The
    write buffer size is 2047 characters and it is not configurable.

    Use ``fsync(STDOUT_FILENO)`` or ``fdatasync(STDOUT_FILENO)`` to drain the
    write buffer.

    The Termios framework is not used.  There is no support to change device
    settings, e.g.  baud, stop bits, parity, etc.

    The

    * ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER``,

    * ``CONFIGURE_APPLICATION_NEEDS_SIMPLE_CONSOLE_DRIVER``, and

    * ``CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER``

    configuration options are mutually exclusive.

.. index:: CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER

.. _CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER:

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.

.. index:: CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER

.. _CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER:

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.

.. index:: CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER

.. _CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER:

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.

.. index:: CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER

.. _CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER:

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.

.. index:: CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER

.. _CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER:

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.

.. index:: CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER

.. _CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER:

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.

.. index:: CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER

.. _CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER:

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.

.. index:: CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS

.. _CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS:

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

.. index:: CONFIGURE_APPLICATION_EXTRA_DRIVERS

.. _CONFIGURE_APPLICATION_EXTRA_DRIVERS:

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.

.. index:: CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER
.. index:: /dev/null

.. _CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER:

CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER
---------------------------------------

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.

.. index:: CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER
.. index:: /dev/zero

.. _CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER:

CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER
---------------------------------------

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.

.. index:: CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE

.. _CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE:

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.

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

This section defines the multiprocessing related system configuration
parameters supported by ``<rtems/confdefs.h>``.  They are only used if RTEMS
was built with the ``--enable-multiprocessing`` build configuration option.
The multiprocessing (MPCI) support must not be confused with the SMP support.

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

.. index:: CONFIGURE_MP_APPLICATION

.. _CONFIGURE_MP_APPLICATION:

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 built with the
    ``--enable-multiprocessing`` build configuration option.

.. index:: CONFIGURE_MP_NODE_NUMBER

.. _CONFIGURE_MP_NODE_NUMBER:

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.

.. index:: CONFIGURE_MP_MAXIMUM_NODES

.. _CONFIGURE_MP_MAXIMUM_NODES:

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.

.. index:: CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS

.. _CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS:

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.

.. index:: CONFIGURE_MP_MAXIMUM_PROXIES

.. _CONFIGURE_MP_MAXIMUM_PROXIES:

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

.. index:: CONFIGURE_MP_MPCI_TABLE_POINTER

.. _CONFIGURE_MP_MPCI_TABLE_POINTER:

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.

.. index:: CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE

.. _CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE:

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.

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.

.. index:: CONFIGURE_GNAT_RTEMS

.. _CONFIGURE_GNAT_RTEMS:

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.

.. index:: CONFIGURE_MAXIMUM_ADA_TASKS

.. _CONFIGURE_MAXIMUM_ADA_TASKS:

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.

.. index:: CONFIGURE_MAXIMUM_FAKE_ADA_TASKS

.. _CONFIGURE_MAXIMUM_FAKE_ADA_TASKS:

CONFIGURE_MAXIMUM_FAKE_ADA_TASKS
--------------------------------

CONSTANT:
    ``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.

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.

Go Tasks
========

.. index:: CONFIGURE_ENABLE_GO

.. _CONFIGURE_ENABLE_GO:

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

.. index:: CONFIGURE_MAXIMUM_GOROUTINES

.. _CONFIGURE_MAXIMUM_GOROUTINES:

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

.. index:: CONFIGURE_MAXIMUM_GO_CHANNELS

.. _CONFIGURE_MAXIMUM_GO_CHANNELS:

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

Obsolete Configuration Options
==============================

.. index:: CONFIGURE_BDBUF_BUFFER_COUNT

CONFIGURE_BDBUF_BUFFER_COUNT
----------------------------

This configuration option was introduced in RTEMS 4.7.0 and is obsolete since
RTEMS 4.10.0.

.. index:: CONFIGURE_BDBUF_BUFFER_SIZE

CONFIGURE_BDBUF_BUFFER_SIZE
---------------------------

This configuration option was introduced in RTEMS 4.7.0 and is obsolete since
RTEMS 4.10.0.

.. index:: CONFIGURE_DISABLE_CLASSIC_API_NOTEPADS

CONFIGURE_DISABLE_CLASSIC_API_NOTEPADS
--------------------------------------

This configuration option was introduced in RTEMS 4.9.0 and is obsolete since
RTEMS 5.1.

.. index:: CONFIGURE_HAS_OWN_CONFIGURATION_TABLE

CONFIGURE_HAS_OWN_CONFIGURATION_TABLE
-------------------------------------

This configuration option is obsolete since RTEMS 5.1.

.. index:: CONFIGURE_HAS_OWN_BDBUF_TABLE

CONFIGURE_HAS_OWN_BDBUF_TABLE
-----------------------------

This configuration option was introduced in RTEMS 4.7.0 and is obsolete since
RTEMS 4.10.0.

.. index:: CONFIGURE_HAS_OWN_MOUNT_TABLE

CONFIGURE_HAS_OWN_MOUNT_TABLE
-----------------------------

This configuration option is obsolete since RTEMS 5.1.

.. index:: CONFIGURE_NUMBER_OF_TERMIOS_PORTS

CONFIGURE_NUMBER_OF_TERMIOS_PORTS
---------------------------------

This configuration option is obsolete since RTEMS 5.1.

.. index:: CONFIGURE_MAXIMUM_POSIX_BARRIERS

CONFIGURE_MAXIMUM_POSIX_BARRIERS
--------------------------------

This configuration option is obsolete since RTEMS 5.1.

.. index:: CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES

CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES
-------------------------------------------

This configuration option is obsolete since RTEMS 5.1.

.. index:: CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUE_DESCRIPTORS

CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUE_DESCRIPTORS
-------------------------------

This configuration option was introduced in RTEMS 4.10.0 and is obsolete since
RTEMS 5.1.

.. index:: CONFIGURE_MAXIMUM_POSIX_MUTEXES

CONFIGURE_MAXIMUM_POSIX_MUTEXES
-------------------------------

This configuration option is obsolete since RTEMS 5.1.

.. index:: CONFIGURE_MAXIMUM_POSIX_RWLOCKS

CONFIGURE_MAXIMUM_POSIX_RWLOCKS
-------------------------------

This configuration option is obsolete since RTEMS 5.1.

.. index:: CONFIGURE_MAXIMUM_POSIX_SPINLOCKS

CONFIGURE_MAXIMUM_POSIX_SPINLOCKS
---------------------------------

This configuration option is obsolete since RTEMS 5.1.

.. index:: CONFIGURE_TERMIOS_DISABLED

CONFIGURE_TERMIOS_DISABLED
--------------------------

This configuration option is obsolete since RTEMS 5.1.

.. index:: CONFIGURE_SMP_APPLICATION

CONFIGURE_SMP_APPLICATION
-------------------------

This configuration option was introduced in RTEMS 4.11.0 and is obsolete since
RTEMS 5.1.

.. index:: CONFIGURE_SMP_MAXIMUM_PROCESSORS

CONFIGURE_SMP_MAXIMUM_PROCESSORS
--------------------------------

This configuration option was introduced in RTEMS 4.11.0 and is obsolete since
RTEMS 5.1.  See also :ref:`CONFIGURE_MAXIMUM_PROCESSORS`.