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Information Related to Event Manager. More...

Collaboration diagram for Events:


 Event Set
 System Events
 System events are similar to normal events.
 Transient Event
 The transient event can be used by a client task to issue a request to another task or interrupt service (server).
 Classic Event Implementation


 Constant used to receive the set of currently pending events in rtems_event_receive().


rtems_status_code rtems_event_send (rtems_id id, rtems_event_set event_in)
 Sends an Event Set to the Target Task. More...
rtems_status_code rtems_event_receive (rtems_event_set event_in, rtems_option option_set, rtems_interval ticks, rtems_event_set *event_out)
 Receives pending events. More...

Detailed Description

Information Related to Event Manager.

The event manager provides a high performance method of intertask communication and synchronization.

This include file contains the information pertaining to the Event Manager. This manager provides a high performance method of communication and synchronization.

Directives provided are:

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:

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.

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.

Function Documentation

rtems_status_code rtems_event_receive ( rtems_event_set  event_in,
rtems_option  option_set,
rtems_interval  ticks,
rtems_event_set event_out 

Receives pending events.

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. The RTEMS_EVENT_ANY and RTEMS_EVENT_ALL are used in the option_set parameter to specify whether at least 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.

A task can determine the pending event set by using a value of RTEMS_PENDING_EVENTS for the input event set event_in. The pending events are returned to the calling task but the event set is left unaltered.

A task can receive all of the currently pending events by using the a value of RTEMS_ALL_EVENTS for the input event set event_in and RTEMS_NO_WAIT | RTEMS_EVENT_ANY for the option set 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.

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.

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.

A clock tick is required to support the wait with time out functionality of this directive.

[in]event_inSet of requested events (input events).
[in]option_setUse a bitwise or of the following options
[in]ticksTime out in ticks. Use RTEMS_NO_TIMEOUT to wait without a time out (potentially forever).
[out]event_outSet of received events (output events).
Return values
RTEMS_SUCCESSFULSuccessful operation.
RTEMS_UNSATISFIEDInput events not satisfied (only with the RTEMS_NO_WAIT option).
RTEMS_INVALID_ADDRESSThe event_out pointer is NULL.
RTEMS_TIMEOUTTimed out waiting for events.
rtems_status_code rtems_event_send ( rtems_id  id,
rtems_event_set  event_in 

Sends an Event Set to the Target Task.

This directive sends an event set event_in to the task specified by id.

Based upon the state of the target task, one of the following situations applies. The 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.
  • not satisfied, then the event set is posted but left pending and the task remains blocked.
  • not waiting for events.
  • The event set is posted and left pending.

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.

[in]idIdentifier of the target task. Specifying RTEMS_SELF results in the event set being sent to the calling task.
[in]event_inEvent set sent to the target task.
Return values
RTEMS_SUCCESSFULSuccessful operation.
RTEMS_INVALID_IDInvalid task identifier.