From 72a62ad88f82fe1ffee50024db4dd0f3fa5806f7 Mon Sep 17 00:00:00 2001 From: Chris Johns Date: Thu, 3 Nov 2016 16:58:08 +1100 Subject: Rename all manuals with an _ to have a -. It helps released naming of files. --- c-user/event_manager.rst | 307 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 307 insertions(+) create mode 100644 c-user/event_manager.rst (limited to 'c-user/event_manager.rst') diff --git a/c-user/event_manager.rst b/c-user/event_manager.rst new file mode 100644 index 0000000..724d138 --- /dev/null +++ b/c-user/event_manager.rst @@ -0,0 +1,307 @@ +.. 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. -- cgit v1.2.3