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diff --git a/c_user/event_manager.rst b/c_user/event_manager.rst deleted file mode 100644 index 724d138..0000000 --- a/c_user/event_manager.rst +++ /dev/null @@ -1,307 +0,0 @@ -.. comment SPDX-License-Identifier: CC-BY-SA-4.0 - -.. COMMENT: COPYRIGHT (c) 1988-2008. -.. COMMENT: On-Line Applications Research Corporation (OAR). -.. COMMENT: All rights reserved. - -Event Manager -############# - -.. index:: events - -Introduction -============ - -The event manager provides a high performance method of intertask communication -and synchronization. The directives provided by the event manager are: - -- rtems_event_send_ - Send event set to a task -- rtems_event_receive_ - Receive event condition - -Background -========== - -Event Sets ----------- -.. index:: event flag, definition -.. index:: event set, definition -.. index:: rtems_event_set - -An event flag is used by a task (or ISR) to inform another task of the -occurrence of a significant situation. Thirty-two event flags are associated -with each task. A collection of one or more event flags is referred to as an -event set. The data type ``rtems_event_set`` is used to manage event sets. - -The application developer should remember the following key characteristics of -event operations when utilizing the event manager: - -- Events provide a simple synchronization facility. - -- Events are aimed at tasks. - -- Tasks can wait on more than one event simultaneously. - -- Events are independent of one another. - -- Events do not hold or transport data. - -- Events are not queued. In other words, if an event is sent more than once to - a task before being received, the second and subsequent send operations to - that same task have no effect. - -An event set is posted when it is directed (or sent) to a task. A pending -event is an event that has been posted but not received. An event condition is -used to specify the event set which the task desires to receive and the -algorithm which will be used to determine when the request is satisfied. An -event condition is satisfied based upon one of two algorithms which are -selected by the user. The ``RTEMS_EVENT_ANY`` algorithm states that an event -condition is satisfied when at least a single requested event is posted. The -``RTEMS_EVENT_ALL`` algorithm states that an event condition is satisfied when -every requested event is posted. - -Building an Event Set or Condition ----------------------------------- -.. index:: event condition, building -.. index:: event set, building - -An event set or condition is built by a bitwise OR of the desired events. The -set of valid events is ``RTEMS_EVENT_0`` through ``RTEMS_EVENT_31``. If an -event is not explicitly specified in the set or condition, then it is not -present. Events are specifically designed to be mutually exclusive, therefore -bitwise OR and addition operations are equivalent as long as each event appears -exactly once in the event set list. - -For example, when sending the event set consisting of ``RTEMS_EVENT_6``, -``RTEMS_EVENT_15``, and ``RTEMS_EVENT_31``, the event parameter to the -``rtems_event_send`` directive should be ``RTEMS_EVENT_6 | RTEMS_EVENT_15 | -RTEMS_EVENT_31``. - -Building an EVENT_RECEIVE Option Set ------------------------------------- - -In general, an option is built by a bitwise OR of the desired option -components. The set of valid options for the ``rtems_event_receive`` directive -are listed in the following table: - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_WAIT`` - - task will wait for event (default) - * - ``RTEMS_NO_WAIT`` - - task should not wait - * - ``RTEMS_EVENT_ALL`` - - return after all events (default) - * - ``RTEMS_EVENT_ANY`` - - return after any events - -Option values are specifically designed to be mutually exclusive, therefore -bitwise OR and addition operations are equivalent as long as each option -appears exactly once in the component list. An option listed as a default is -not required to appear in the option list, although it is a good programming -practice to specify default options. If all defaults are desired, the option -``RTEMS_DEFAULT_OPTIONS`` should be specified on this call. - -This example demonstrates the option parameter needed to poll for all events in -a particular event condition to arrive. The option parameter passed to the -``rtems_event_receive`` directive should be either ``RTEMS_EVENT_ALL | -RTEMS_NO_WAIT`` or ``RTEMS_NO_WAIT``. The option parameter can be set to -``RTEMS_NO_WAIT`` because ``RTEMS_EVENT_ALL`` is the default condition for -``rtems_event_receive``. - -Operations -========== - -Sending an Event Set --------------------- - -The ``rtems_event_send`` directive allows a task (or an ISR) to direct an event -set to a target task. Based upon the state of the target task, one of the -following situations applies: - -- Target Task is Blocked Waiting for Events - - - If the waiting task's input event condition is satisfied, then the task is - made ready for execution. - - - If the waiting task's input event condition is not satisfied, then the - event set is posted but left pending and the task remains blocked. - -- Target Task is Not Waiting for Events - - - The event set is posted and left pending. - -Receiving an Event Set ----------------------- - -The ``rtems_event_receive`` directive is used by tasks to accept a specific -input event condition. The task also specifies whether the request is -satisfied when all requested events are available or any single requested event -is available. If the requested event condition is satisfied by pending events, -then a successful return code and the satisfying event set are returned -immediately. If the condition is not satisfied, then one of the following -situations applies: - -- By default, the calling task will wait forever for the event condition to be - satisfied. - -- Specifying the ``RTEMS_NO_WAIT`` option forces an immediate return with an - error status code. - -- Specifying a timeout limits the period the task will wait before returning - with an error status code. - -Determining the Pending Event Set ---------------------------------- - -A task can determine the pending event set by calling the -``rtems_event_receive`` directive with a value of ``RTEMS_PENDING_EVENTS`` for -the input event condition. The pending events are returned to the calling task -but the event set is left unaltered. - -Receiving all Pending Events ----------------------------- - -A task can receive all of the currently pending events by calling the -``rtems_event_receive`` directive with a value of ``RTEMS_ALL_EVENTS`` for the -input event condition and ``RTEMS_NO_WAIT | RTEMS_EVENT_ANY`` for the option -set. The pending events are returned to the calling task and the event set is -cleared. If no events are pending then the ``RTEMS_UNSATISFIED`` status code -will be returned. - -Directives -========== - -This section details the event manager's directives. A subsection is dedicated -to each of this manager's directives and describes the calling sequence, -related constants, usage, and status codes. - -.. _rtems_event_send: - -EVENT_SEND - Send event set to a task -------------------------------------- -.. index:: send event set to a task - -**CALLING SEQUENCE:** - -.. index:: rtems_event_send - -.. code-block:: c - - rtems_status_code rtems_event_send ( - rtems_id id, - rtems_event_set event_in - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - event set sent successfully - * - ``RTEMS_INVALID_ID`` - - invalid task id - -**DESCRIPTION:** - -This directive sends an event set, event_in, to the task specified by id. If a -blocked task's input event condition is satisfied by this directive, then it -will be made ready. If its input event condition is not satisfied, then the -events satisfied are updated and the events not satisfied are left pending. If -the task specified by id is not blocked waiting for events, then the events -sent are left pending. - -**NOTES:** - -Specifying ``RTEMS_SELF`` for id results in the event set being sent to the -calling task. - -Identical events sent to a task are not queued. In other words, the second, -and subsequent, posting of an event to a task before it can perform an -``rtems_event_receive`` has no effect. - -The calling task will be preempted if it has preemption enabled and a higher -priority task is unblocked as the result of this directive. - -Sending an event set to a global task which does not reside on the local node -will generate a request telling the remote node to send the event set to the -appropriate task. - -.. _rtems_event_receive: - -EVENT_RECEIVE - Receive event condition ---------------------------------------- -.. index:: receive event condition - -**CALLING SEQUENCE:** - -.. index:: rtems_event_receive - -.. code-block:: c - - rtems_status_code rtems_event_receive ( - rtems_event_set event_in, - rtems_option option_set, - rtems_interval ticks, - rtems_event_set *event_out - ); - -**DIRECTIVE STATUS CODES:** - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_SUCCESSFUL`` - - event received successfully - * - ``RTEMS_UNSATISFIED`` - - input event not satisfied (``RTEMS_NO_WAIT``) - * - ``RTEMS_INVALID_ADDRESS`` - - ``event_out`` is NULL - * - ``RTEMS_TIMEOUT`` - - timed out waiting for event - -**DESCRIPTION:** - -This directive attempts to receive the event condition specified in event_in. -If event_in is set to ``RTEMS_PENDING_EVENTS``, then the current pending events -are returned in event_out and left pending. The ``RTEMS_WAIT`` and -``RTEMS_NO_WAIT`` options in the option_set parameter are used to specify -whether or not the task is willing to wait for the event condition to be -satisfied. ``RTEMS_EVENT_ANY`` and ``RTEMS_EVENT_ALL`` are used in the -option_set parameter are used to specify whether a single event or the complete -event set is necessary to satisfy the event condition. The event_out parameter -is returned to the calling task with the value that corresponds to the events -in event_in that were satisfied. - -If pending events satisfy the event condition, then event_out is set to the -satisfied events and the pending events in the event condition are cleared. If -the event condition is not satisfied and ``RTEMS_NO_WAIT`` is specified, then -event_out is set to the currently satisfied events. If the calling task -chooses to wait, then it will block waiting for the event condition. - -If the calling task must wait for the event condition to be satisfied, then the -timeout parameter is used to specify the maximum interval to wait. If it is -set to ``RTEMS_NO_TIMEOUT``, then the calling task will wait forever. - -**NOTES:** - -This directive only affects the events specified in event_in. Any pending -events that do not correspond to any of the events specified in event_in will -be left pending. - -The following event receive option constants are defined by RTEMS: - -.. list-table:: - :class: rtems-table - - * - ``RTEMS_WAIT`` - - task will wait for event (default) - * - ``RTEMS_NO_WAIT`` - - task should not wait - * - ``RTEMS_EVENT_ALL`` - - return after all events (default) - * - ``RTEMS_EVENT_ANY`` - - return after any events - -A clock tick is required to support the functionality of this directive. |