source: rtems-docs/c_user/configuring_a_system.rst @ 170418a

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

Configuring a System
####################

.. COMMENT: === Introduction ===

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

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

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

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

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

.. sidebar: Trivia:

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

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

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

.. COMMENT: === Philosophy ===

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

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

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

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

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

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

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

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

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

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

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

- a configuration parameter is changed,

- task or interrupt stack sizes change,

- the floating point attribute of a task changes,

- task floating point attribute is altered,

- RTEMS is upgraded, or

- the target processor is changed.

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

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

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

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

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

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

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

- Memory for messages is not included.

- Device driver requirements are not included.

- Network stack requirements are not included.

- Requirements for add-on libraries are not included.

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

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

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

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

*DATA TYPE:*
  Please refer to all existing formats.

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

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

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

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

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

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

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

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

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

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

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

*NOTES:*
  Any further notes. (No specific format)

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

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

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

.. code-block:: c

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Unlimited Objects
-----------------

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

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

- POSIX Keys

- POSIX Key Value Pairs

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

- Tasks

- Timers

- Semaphores

- Message Queues

- Periods

- Barriers

- Partitions

- Regions

- Ports

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

- Threads

- Mutexes

- Condition Variables

- Timers

- Message Queues

- Message Queue Descriptors

- Semaphores

- Barriers

- Read/Write Locks

- Spinlocks

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

- Drivers

- File Descriptors

- User Extensions

- POSIX Queued Signals

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

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

.. code-block:: c

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

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

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

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

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

.. code-block:: c

    #define CONFIGURE_MAXIMUM_TASKS rtems_resource_unlimited(5)

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

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

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

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

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

.. COMMENT: === CONFIGURE_UNLIMITED_OBJECTS ===

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

*CONSTANT:*
    ``CONFIGURE_UNLIMITED_OBJECTS``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_UNLIMITED_ALLOCATION_SIZE ===

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

*CONSTANT:*
    ``CONFIGURE_UNLIMITED_ALLOCATION_SIZE``

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

*RANGE:*
    Positive.

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

**DESCRIPTION:**

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

**NOTES:**

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

.. code-block:: c

    #define CONFIGURE_UNLIMITED_OBJECTS
    #define CONFIGURE_UNLIMITED_ALLOCATION_SIZE 5

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

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

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

.. COMMENT: === CONFIGURE_MAXIMUM_TASKS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_TASKS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

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

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

.. COMMENT: XXX - Add xref to 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: === CONFIGURE_MAXIMUM_TIMERS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_TIMERS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_SEMAPHORES ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_SEMAPHORES``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_MRSP_SEMAPHORES ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_MRSP_SEMAPHORES``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_MAXIMUM_MESSAGE_QUEUES ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_MESSAGE_QUEUES``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_BARRIERS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_BARRIERS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_PERIODS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_PERIODS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_PARTITIONS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_PARTITIONS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_REGIONS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_REGIONS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_MAXIMUM_PORTS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_PORTS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_USER_EXTENSIONS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_USER_EXTENSIONS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

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

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

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

.. COMMENT: === CONFIGURE_RTEMS_INIT_TASKS_TABLE ===

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

*CONSTANT:*
    ``CONFIGURE_RTEMS_INIT_TASKS_TABLE``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_INIT_TASK_ENTRY_POINT ===

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

*CONSTANT:*
    ``CONFIGURE_INIT_TASK_ENTRY_POINT``

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

*RANGE:*
    Valid task entry function pointer.

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

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_INIT_TASK_NAME ===

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

*CONSTANT:*
    ``CONFIGURE_INIT_TASK_NAME``

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

*RANGE:*
    Any value.

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

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_INIT_TASK_STACK_SIZE ===

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

*CONSTANT:*
    ``CONFIGURE_INIT_TASK_STACK_SIZE``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is RTEMS_MINIMUM_STACK_SIZE.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_INIT_TASK_PRIORITY ===

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

*CONSTANT:*
    ``CONFIGURE_INIT_TASK_PRIORITY``

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

*RANGE:*
    One (1) to CONFIGURE_MAXIMUM_PRIORITY.

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

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_INIT_TASK_ATTRIBUTES ===

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

*CONSTANT:*
    ``CONFIGURE_INIT_TASK_ATTRIBUTES``

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

*RANGE:*
    Valid task attribute sets.

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

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_INIT_TASK_INITIAL_MODES ===

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

*CONSTANT:*
    ``CONFIGURE_INIT_TASK_INITIAL_MODES``

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

*RANGE:*
    Valid task mode sets.

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

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_INIT_TASK_ARGUMENTS ===

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

*CONSTANT:*
    ``CONFIGURE_INIT_TASK_ARGUMENTS``

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

*RANGE:*
    Complete range of the type.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_HAS_OWN_INIT_TASK_TABLE ===

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

*CONSTANT:*
    ``CONFIGURE_HAS_OWN_INIT_TASK_TABLE``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

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

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

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

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_THREADS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_POSIX_THREADS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

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

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

All POSIX threads have floating point enabled.

.. COMMENT: XXX - Add xref to CONFIGURE_MAXIMUM_TASKS.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_MUTEXES ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_POSIX_MUTEXES``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_KEYS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_POSIX_KEYS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: XXX - Key pairs

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_TIMERS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_POSIX_TIMERS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: XXX - memory for buffers note

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUE_DESCRIPTORS ===

Specify Maximum POSIX API Message Queue Descriptors
---------------------------------------------------
.. index:: CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUE_DESCRIPTORS

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUE_DESCRIPTORS``

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

*RANGE:*
    greater than or equal to ``CONFIGURE_MAXIMUM_POSIX_MESSAGES_QUEUES``

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUE_DESCRIPTORS`` is the maximum number of
POSIX API Message Queue Descriptors that can be concurrently active.

**NOTES:**

This object class can be configured in unlimited allocation mode.

``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUE_DESCRIPTORS`` should be greater than or
equal to ``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES``.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_SEMAPHORES ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_POSIX_SEMAPHORES``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_BARRIERS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_POSIX_BARRIERS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_SPINLOCKS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_POSIX_SPINLOCKS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_RWLOCKS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_POSIX_RWLOCKS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

This object class can be configured in unlimited allocation mode.

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

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

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

.. COMMENT: === CONFIGURE_POSIX_INIT_THREAD_TABLE ===

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

*CONSTANT:*
    .. index:: CONFIGURE_POSIX_INIT_THREAD_TABLE

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

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

**DESCRIPTION:**

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

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT ===

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

*CONSTANT:*
    ``CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT``

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

*RANGE:*
    Undefined or a valid POSIX thread function pointer.

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

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_POSIX_INIT_THREAD_STACK_SIZE ===

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

*CONSTANT:*
    ``CONFIGURE_POSIX_INIT_THREAD_STACK_SIZE``

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

*RANGE:*
    Zero or positive.

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

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE ===

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

*CONSTANT:*
    ``CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

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

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

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

.. COMMENT: === CONFIGURE_UNIFIED_WORK_AREAS ===


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

*CONSTANT:*
    ``CONFIGURE_UNIFIED_WORK_AREAS``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

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

**DESCRIPTION:**

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

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_MICROSECONDS_PER_TICK ===

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

*CONSTANT:*
    ``CONFIGURE_MICROSECONDS_PER_TICK``

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

*RANGE:*
    Positive.

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

**DESCRIPTION:**

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

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

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

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_TICKS_PER_TIMESLICE ===

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

*CONSTANT:*
    ``CONFIGURE_TICKS_PER_TIMESLICE``

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

*RANGE:*
    Positive.

*DEFAULT VALUE:*
    The default value is 50.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_MAXIMUM_PRIORITY ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_PRIORITY``

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

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

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

**DESCRIPTION:**

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

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

**NOTES:**

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

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

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

.. COMMENT: === CONFIGURE_MINIMUM_TASK_STACK_SIZE ===

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

*CONSTANT:*
    ``CONFIGURE_MINIMUM_TASK_STACK_SIZE``

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

*RANGE:*
    Positive.

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

**DESCRIPTION:**

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

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_INTERRUPT_STACK_SIZE ===

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

*CONSTANT:*
    ``CONFIGURE_INTERRUPT_STACK_SIZE``

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

*RANGE:*
    Positive.

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

**DESCRIPTION:**

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_EXTRA_TASK_STACKS ===


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

*CONSTANT:*
    ``CONFIGURE_EXTRA_TASK_STACKS``

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

*RANGE:*
    Undefined or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY ===

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

*CONSTANT:*
    ``CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

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

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_STACK_CHECKER_ENABLED ===

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

*CONSTANT:*
    ``CONFIGURE_STACK_CHECKER_ENABLED``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

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

**DESCRIPTION:**

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_INITIAL_EXTENSIONS ===

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

*CONSTANT:*
    ``CONFIGURE_INITIAL_EXTENSIONS``

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

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

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

None.

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

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

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

.. COMMENT: === CONFIGURE_TASK_STACK_ALLOCATOR_INIT ===

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

*CONSTANT:*
    ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT``

*DATA TYPE:*
    Function pointer.

*RANGE:*
    Undefined, NULL or valid function pointer.

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

**DESCRIPTION:**

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

**NOTES:**

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

- ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT``

- ``CONFIGURE_TASK_STACK_ALLOCATOR``

- ``CONFIGURE_TASK_STACK_DEALLOCATOR``

.. COMMENT: === CONFIGURE_TASK_STACK_ALLOCATOR ===

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

.. index:: task stack allocator

*CONSTANT:*
    ``CONFIGURE_TASK_STACK_ALLOCATOR``

*DATA TYPE:*
    Function pointer.

*RANGE:*
    Undefined or valid function pointer.

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

**DESCRIPTION:**

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

**NOTES:**

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

- ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT``

- ``CONFIGURE_TASK_STACK_ALLOCATOR``

- ``CONFIGURE_TASK_STACK_DEALLOCATOR``

.. COMMENT: === CONFIGURE_TASK_STACK_DEALLOCATOR ===

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

*CONSTANT:*
    ``CONFIGURE_TASK_STACK_DEALLOCATOR``

*DATA TYPE:*
    Function pointer.

*RANGE:*
    Undefined or valid function pointer.

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

**DESCRIPTION:**

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

**NOTES:**

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

- ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT``

- ``CONFIGURE_TASK_STACK_ALLOCATOR``

- ``CONFIGURE_TASK_STACK_DEALLOCATOR``

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

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

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

.. COMMENT: === CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE ===

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

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

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

*RANGE:*
    Positive.

*DEFAULT VALUE:*
    The default value is None.

**DESCRIPTION:**

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

The interface for this macro is as follows:

.. code-block:: c

    CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE(max_messages, size_per)

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_MESSAGE_BUFFER_MEMORY ===

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

*CONSTANT:*
    ``CONFIGURE_MESSAGE_BUFFER_MEMORY``

*DATA TYPE:*
    integer summation macro

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

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

**DESCRIPTION:**

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

**NOTES:**

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

.. code-block:: c

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

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

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

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

.. COMMENT: === CONFIGURE_MEMORY_OVERHEAD ===


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

*CONSTANT:*
    ``CONFIGURE_MEMORY_OVERHEAD``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_HAS_OWN_CONFIGURATION_TABLE ===

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

*CONSTANT:*
    ``CONFIGURE_HAS_OWN_CONFIGURATION_TABLE``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

None.

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

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

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

.. COMMENT: === CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS ===

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

*CONSTANT:*
    ``CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS``

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

*RANGE:*
    Zero or positive.

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

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_TERMIOS_DISABLED ===

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

*CONSTANT:*
    ``CONFIGURE_TERMIOS_DISABLED``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

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

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_NUMBER_OF_TERMIOS_PORTS ===

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

*CONSTANT:*
    ``CONFIGURE_NUMBER_OF_TERMIOS_PORTS``

*DATA TYPE:*
    Unsigned integer.

*RANGE:*
    Zero or positive.

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

**DESCRIPTION:**

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

**NOTES:**

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

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

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

This section defines File System related configuration parameters.

.. COMMENT: === CONFIGURE_HAS_OWN_MOUNT_TABLE ===

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

*CONSTANT:*
    ``CONFIGURE_HAS_OWN_MOUNT_TABLE``

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

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

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

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

**NOTES:**

None.

.. COMMENT: XXX - Please provide an example

.. COMMENT: === CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM ===

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

*CONSTANT:*
    ``CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

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

**DESCRIPTION:**

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_MAXIMUM_DEVICES ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_DEVICES``

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

*RANGE:*
    Positive.

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

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_APPLICATION_DISABLE_FILESYSTEM ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_DISABLE_FILESYSTEM``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

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

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM ===

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

*CONSTANT:*
    ``CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

- ``CONFIGURE_IMFS_DISABLE_CHMOD``,

- ``CONFIGURE_IMFS_DISABLE_CHOWN``,

- ``CONFIGURE_IMFS_DISABLE_UTIME``,

- ``CONFIGURE_IMFS_DISABLE_LINK``,

- ``CONFIGURE_IMFS_DISABLE_SYMLINK``,

- ``CONFIGURE_IMFS_DISABLE_READLINK``,

- ``CONFIGURE_IMFS_DISABLE_RENAME``, and

- ``CONFIGURE_IMFS_DISABLE_UNMOUNT``.

.. COMMENT: === CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK``

*DATA TYPE:*
    Boolean feature macro.

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

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

**DESCRIPTION:**

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

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

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

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

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

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

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

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_CHOWN ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_CHOWN``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_CHMOD ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_CHMOD``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_UTIME ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_UTIME``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_LINK ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_LINK``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_SYMLINK ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_SYMLINK``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_READLINK ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_READLINK``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_RENAME ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_RENAME``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_READDIR ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_READDIR``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_MOUNT ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_MOUNT``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_UNMOUNT ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_UNMOUNT``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_MKNOD ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_MKNOD``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_MKNOD_FILE ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_MKNOD_FILE``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

.. COMMENT: === CONFIGURE_IMFS_DISABLE_RMNOD ===

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

*CONSTANT:*
    ``CONFIGURE_IMFS_DISABLE_RMNOD``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

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

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

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

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_LIBBLOCK ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_NEEDS_LIBBLOCK``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

Provides a Block Device Cache configuration.

**NOTES:**

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

.. COMMENT: === CONFIGURE_BDBUF_CACHE_MEMORY_SIZE ===

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

*CONSTANT:*
    ``CONFIGURE_BDBUF_CACHE_MEMORY_SIZE``

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

*RANGE:*
    Positive.

*DEFAULT VALUE:*
    The default value is 32768 bytes.

**DESCRIPTION:**

Size of the cache memory in bytes.

**NOTES:**

None.

.. COMMENT: === CONFIGURE_BDBUF_BUFFER_MIN_SIZE ===

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

*CONSTANT:*
    ``CONFIGURE_BDBUF_BUFFER_MIN_SIZE``

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

*RANGE:*
    Positive.

*DEFAULT VALUE:*
    The default value is 512 bytes.

**DESCRIPTION:**

Defines the minimum size of a buffer in bytes.

**NOTES:**

None.

.. COMMENT: === CONFIGURE_BDBUF_BUFFER_MAX_SIZE ===

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

*CONSTANT:*
    ``CONFIGURE_BDBUF_BUFFER_MAX_SIZE``

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

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

*DEFAULT VALUE:*
    The default value is 4096 bytes.

**DESCRIPTION:**

Defines the maximum size of a buffer in bytes.

**NOTES:**

None.

.. COMMENT: === CONFIGURE_SWAPOUT_SWAP_PERIOD ===

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

*CONSTANT:*
    ``CONFIGURE_SWAPOUT_SWAP_PERIOD``

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

*RANGE:*
    Positive.

*DEFAULT VALUE:*
    The default value is 250 milliseconds.

**DESCRIPTION:**

Defines the swapout task swap period in milliseconds.

**NOTES:**

None.

.. COMMENT: === CONFIGURE_SWAPOUT_BLOCK_HOLD ===

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

*CONSTANT:*
    ``CONFIGURE_SWAPOUT_BLOCK_HOLD``

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

*RANGE:*
    Positive.

*DEFAULT VALUE:*
    The default value is 1000 milliseconds.

**DESCRIPTION:**

Defines the swapout task maximum block hold time in milliseconds.

**NOTES:**

None.

.. COMMENT: === CONFIGURE_SWAPOUT_TASK_PRIORITY ===

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

*CONSTANT:*
    ``CONFIGURE_SWAPOUT_TASK_PRIORITY``

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

*RANGE:*
    Valid task priority.

*DEFAULT VALUE:*
    The default value is 15.

**DESCRIPTION:**

Defines the swapout task priority.

**NOTES:**

None.

.. COMMENT: === CONFIGURE_BDBUF_MAX_READ_AHEAD_BLOCKS ===

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

*CONSTANT:*
    ``CONFIGURE_BDBUF_MAX_READ_AHEAD_BLOCKS``

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

*RANGE:*
    Positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

Defines the maximum blocks per read-ahead request.

**NOTES:**

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

.. COMMENT: === CONFIGURE_BDBUF_MAX_WRITE_BLOCKS ===

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

*CONSTANT:*
    ``CONFIGURE_BDBUF_MAX_WRITE_BLOCKS``

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

*RANGE:*
    Positive.

*DEFAULT VALUE:*
    The default value is 16.

**DESCRIPTION:**

Defines the maximum blocks per write request.

**NOTES:**

None.

.. COMMENT: === CONFIGURE_BDBUF_TASK_STACK_SIZE ===

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

*CONSTANT:*
    ``CONFIGURE_BDBUF_TASK_STACK_SIZE``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is RTEMS_MINIMUM_STACK_SIZE.

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_BDBUF_READ_AHEAD_TASK_PRIORITY ===

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

*CONSTANT:*
    ``CONFIGURE_BDBUF_READ_AHEAD_TASK_PRIORITY``

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

*RANGE:*
    Valid task priority.

*DEFAULT VALUE:*
    The default value is 15.

**DESCRIPTION:**

Defines the read-ahead task priority.

**NOTES:**

None.

.. COMMENT: === CONFIGURE_SWAPOUT_WORKER_TASKS ===

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

*CONSTANT:*
    ``CONFIGURE_SWAPOUT_WORKER_TASKS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

Defines the swapout worker task count.

**NOTES:**

None.

.. COMMENT: === CONFIGURE_SWAPOUT_WORKER_TASK_PRIORITY ===

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

*CONSTANT:*
    ``CONFIGURE_SWAPOUT_WORKER_TASK_PRIORITY``

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

*RANGE:*
    Valid task priority.

*DEFAULT VALUE:*
    The default value is 15.

**DESCRIPTION:**

Defines the swapout worker task priority.

**NOTES:**

None.

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

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

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

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

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

*CONSTANT:*
    ``CONFIGURE_DISABLE_BSP_SETTINGS``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK ===

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

*CONSTANT:*
    ``CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This option is BSP specific.

**DESCRIPTION:**

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

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

**NOTES:**

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

.. COMMENT: === BSP_IDLE_TASK_BODY ===

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

*CONSTANT:*
    ``BSP_IDLE_TASK_BODY``

*DATA TYPE:*
    Function pointer.

*RANGE:*
    Undefined or valid function pointer.

*DEFAULT VALUE:*
    This option is BSP specific.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === BSP_IDLE_TASK_STACK_SIZE ===

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

*CONSTANT:*
    ``BSP_IDLE_TASK_STACK_SIZE``

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

*RANGE:*
    Undefined or positive.

*DEFAULT VALUE:*
    This option is BSP specific.

**DESCRIPTION:**

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

**NOTES:**

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

- RTEMS default minimum stack size.

- If defined, then ``CONFIGURE_MINIMUM_TASK_STACK_SIZE``.

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

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

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

.. COMMENT: === BSP_INITIAL_EXTENSION ===

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

*CONSTANT:*
    ``BSP_INITIAL_EXTENSION``

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

*RANGE:*
    Undefined or a list of user extension initializers.

*DEFAULT VALUE:*
    This option is BSP specific.

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === BSP_INTERRUPT_STACK_SIZE ===

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

*CONSTANT:*
    ``BSP_INTERRUPT_STACK_SIZE``

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

*RANGE:*
    Undefined or positive.

*DEFAULT VALUE:*
    This option is BSP specific.

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === BSP_MAXIMUM_DEVICES ===

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

*CONSTANT:*
    ``BSP_MAXIMUM_DEVICES``

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

*RANGE:*
    Undefined or positive.

*DEFAULT VALUE:*
    This option is BSP specific.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === BSP_ZERO_WORKSPACE_AUTOMATICALLY ===

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

*CONSTANT:*
    ``BSP_ZERO_WORKSPACE_AUTOMATICALLY``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This option is BSP specific.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_BSP_PREREQUISITE_DRIVERS ===

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

*CONSTANT:*
    ``CONFIGURE_BSP_PREREQUISITE_DRIVERS``

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

*RANGE:*
    Undefined or array of device drivers.

*DEFAULT VALUE:*
    This option is BSP specific.

**DESCRIPTION:**

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

**NOTES:**

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

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

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

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

.. COMMENT: === CONFIGURE_IDLE_TASK_BODY ===

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

*CONSTANT:*
    ``CONFIGURE_IDLE_TASK_BODY``

*DATA TYPE:*
    Function pointer.

*RANGE:*
    Undefined or valid function pointer.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_IDLE_TASK_STACK_SIZE ===

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

*CONSTANT:*
    ``CONFIGURE_IDLE_TASK_STACK_SIZE``

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

*RANGE:*
    Undefined or positive.

*DEFAULT VALUE:*
    The default value is RTEMS_MINIMUM_STACK_SIZE.

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION ===

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

*CONSTANT:*
    ``CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

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

**DESCRIPTION:**

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

**NOTES:**

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

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

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

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

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

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

.. COMMENT: === CONFIGURE_SCHEDULER_PRIORITY ===

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

*CONSTANT:*
    ``CONFIGURE_SCHEDULER_PRIORITY``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

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

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_SCHEDULER_SIMPLE ===

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

*CONSTANT:*
    ``CONFIGURE_SCHEDULER_SIMPLE``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_SCHEDULER_EDF ===

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

*CONSTANT:*
    ``CONFIGURE_SCHEDULER_EDF``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_SCHEDULER_CBS ===

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

*CONSTANT:*
    ``CONFIGURE_SCHEDULER_CBS``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

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

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_SCHEDULER_PRIORITY_SMP ===

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

*CONSTANT:*
    ``CONFIGURE_SCHEDULER_PRIORITY_SMP``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_SCHEDULER_SIMPLE_SMP ===

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

*CONSTANT:*
    ``CONFIGURE_SCHEDULER_SIMPLE_SMP``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

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

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

**NOTES:**

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

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

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

*CONSTANT:*
    ``CONFIGURE_SCHEDULER_NAME``

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

*RANGE:*
    Any value.

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

**DESCRIPTION:**

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

**NOTES:**

None.

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

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

*CONSTANT:*
    ``CONFIGURE_SCHEDULER_USER``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

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

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

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

**NOTES:**

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

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


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

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

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

# How is the set of processors partitioned into clusters?

# Which scheduler is used for which cluster?

**CONFIGURATION:**

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

- ``CONFIGURE_SCHEDULER_PRIORITY_SMP``,

- ``CONFIGURE_SCHEDULER_SIMPLE_SMP``, and

- ``CONFIGURE_SCHEDULER_PRIORITY_AFFINITY_SMP``.

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

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

- ``RTEMS_SCHEDULER_CONTEXT_SIMPLE_SMP(name)``, and

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

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

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

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

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

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

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

- ``RTEMS_SCHEDULER_ASSIGN_DEFAULT``,

- ``RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY``, and

- ``RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL``.

**ERRORS:**

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

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

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

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

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

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

**EXAMPLE:**

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

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

.. code-block:: c

    #define CONFIGURE_SMP_MAXIMUM_PROCESSORS 8
    #define CONFIGURE_MAXIMUM_PRIORITY 255
    /* Make the scheduler algorithm available */
    #define CONFIGURE_SCHEDULER_PRIORITY_SMP
    #include <rtems/scheduler.h>
    /* Create contexts for the two scheduler instances */
    RTEMS_SCHEDULER_CONTEXT_PRIORITY_SMP(io, CONFIGURE_MAXIMUM_PRIORITY + 1);
    RTEMS_SCHEDULER_CONTEXT_PRIORITY_SMP(work, CONFIGURE_MAXIMUM_PRIORITY + 1);
    /* Define the scheduler table */
    #define CONFIGURE_SCHEDULER_CONTROLS \\
                RTEMS_SCHEDULER_CONTROL_PRIORITY_SMP( \
                    io, \
                    rtems_build_name('I', 'O', ' ', ' ') \
                ), \
                RTEMS_SCHEDULER_CONTROL_PRIORITY_SMP( \
                    work, \
                    rtems_build_name('W', 'O', 'R', 'K') \
                )
    /* Define the processor to scheduler assignments */
    #define CONFIGURE_SMP_SCHEDULER_ASSIGNMENTS \
                RTEMS_SCHEDULER_ASSIGN(0, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY), \
                RTEMS_SCHEDULER_ASSIGN_NO_SCHEDULER, \
                RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY), \
                RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY), \
                RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL), \
                RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL), \
                RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL), \
                RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL)

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

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

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

.. COMMENT: XXX - add -enable-smp

.. COMMENT: === CONFIGURE_SMP_APPLICATION ===


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

*CONSTANT:*
    ``CONFIGURE_SMP_APPLICATION``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_SMP_MAXIMUM_PROCESSORS ===

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

*CONSTANT:*
    ``CONFIGURE_SMP_MAXIMUM_PROCESSORS``

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

*RANGE:*
    Defined or undefined.

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

**DESCRIPTION:**

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

**NOTES:**

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

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

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

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

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

.. COMMENT: === CONFIGURE_MAXIMUM_DRIVERS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_DRIVERS``

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

*RANGE:*
    Zero or positive.

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

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

This device driver is responsible for providing a regular interrupt which
invokes the ``rtems_clock_tick`` directive.

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

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS``

*DATA TYPE:*
    device driver entry structures

*RANGE:*
    Undefined or set of device driver entry structures

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: XXX Add example

.. COMMENT: === CONFIGURE_APPLICATION_EXTRA_DRIVERS ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_EXTRA_DRIVERS``

*DATA TYPE:*
    device driver entry structures

*RANGE:*
    Undefined or set of device driver entry structures

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

This device driver is supported by all BSPs.

.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER ===

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

*CONSTANT:*
    ``CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

This device driver is supported by all BSPs.

.. COMMENT: === CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE ===

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

*CONSTANT:*
    ``CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

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

**DESCRIPTION:**

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

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

**NOTES:**

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

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

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

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

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

.. COMMENT: === CONFIGURE_MP_APPLICATION ===

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

*CONSTANT:*
    ``CONFIGURE_MP_APPLICATION``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_MP_NODE_NUMBER ===

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

*CONSTANT:*
    ``CONFIGURE_MP_NODE_NUMBER``

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

*RANGE:*
    Positive.

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

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_MP_MAXIMUM_NODES ===

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

*CONSTANT:*
    ``CONFIGURE_MP_MAXIMUM_NODES``

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

*RANGE:*
    Positive.

*DEFAULT VALUE:*
    The default value is 2.

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS ===

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

*CONSTANT:*
    ``CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS``

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

*RANGE:*
    Positive.

*DEFAULT VALUE:*
    The default value is 32.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_MP_MAXIMUM_PROXIES ===

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

*CONSTANT:*
    ``CONFIGURE_MP_MAXIMUM_PROXIES``

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

*RANGE:*
    Undefined or positive.

*DEFAULT VALUE:*
    The default value is 32.

**DESCRIPTION:**

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

**NOTES:**

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

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

.. COMMENT: === CONFIGURE_MP_MPCI_TABLE_POINTER ===

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

*CONSTANT:*
    ``CONFIGURE_MP_MPCI_TABLE_POINTER``

*DATA TYPE:*
    pointer to ``rtems_mpci_table``

*RANGE:*
    undefined or valid pointer

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE ===

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

*CONSTANT:*
    ``CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

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

Ada Tasks
=========

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

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

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

.. COMMENT: === CONFIGURE_GNAT_RTEMS ===

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

*CONSTANT:*
    ``CONFIGURE_GNAT_RTEMS``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

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

.. COMMENT: === CONFIGURE_MAXIMUM_ADA_TASKS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_ADA_TASKS``

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

*RANGE:*
    Undefined or positive.

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

**DESCRIPTION:**

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

**NOTES:**

None.

.. COMMENT: === CONFIGURE_MAXIMUM_FAKE_ADA_TASKS ===

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

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

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 0.

**DESCRIPTION:**

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

**NOTES:**

None.

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

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

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

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

.. index:: PCI_LIB_AUTO

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

.. index:: PCI_LIB_READ

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

.. index:: PCI_LIB_STATIC

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

.. index:: PCI_LIB_PERIPHERAL

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

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

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

Go Tasks
========

.. COMMENT: === CONFIGURE_ENABLE_GO ===

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

*CONSTANT:*
    ``CONFIGURE_ENABLE_GO``

*DATA TYPE:*
    Boolean feature macro.

*RANGE:*
    Defined or undefined.

*DEFAULT VALUE:*
    This is not defined by default.

**DESCRIPTION:**

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

**NOTES:**

The Go language support is experimental

.. COMMENT: === CONFIGURE_MAXIMUM_GOROUTINES ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_GOROUTINES``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 400

**DESCRIPTION:**

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

**NOTES:**

The Go language support is experimental

.. COMMENT: === CONFIGURE_MAXIMUM_GO_CHANNELS ===

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

*CONSTANT:*
    ``CONFIGURE_MAXIMUM_GO_CHANNELS``

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

*RANGE:*
    Zero or positive.

*DEFAULT VALUE:*
    The default value is 500

**DESCRIPTION:**

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

**NOTES:**

The Go language support is experimental

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

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

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

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