source: rtems-docs/c_user/configuring_a_system.rst @ d389819

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.

Trivia: ``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 `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 `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:: 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 `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 `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:: 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:: 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:: 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 `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 `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 `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:: 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:: 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:: 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`` is 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`` is 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`` is 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`` is 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.

.. COMMENT: COPYRIGHT (c) 1988-2007.

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

.. COMMENT: All rights reserved.