Directives

15.4. Directives#

This section details the directives of the Event Manager. A subsection is dedicated to each of this manager’s directives and lists the calling sequence, parameters, description, return values, and notes of the directive.

15.4.1. rtems_event_send()#

Sends the event set to the task.

CALLING SEQUENCE:

rtems_status_code rtems_event_send( rtems_id id, rtems_event_set event_in );

PARAMETERS:

id

This parameter is the identifier of the target task to receive the event set.

event_in

This parameter is the event set to send.

DESCRIPTION:

This directive sends the event set, event_in, to the target task identified by id. Based upon the state of the target task, one of the following situations applies:

  • The target task is blocked waiting for events, then

    • if the waiting task’s input event condition is satisfied, then the task is made ready for execution, or

    • otherwise, the event set is posted but left pending and the task remains blocked.

  • The target task is not waiting for events, then the event set is posted and left pending.

RETURN VALUES:

RTEMS_SUCCESSFUL

The requested operation was successful.

RTEMS_INVALID_ID

There was no task associated with the identifier specified by id.

NOTES:

Events can be sent by tasks or an ISR.

Specifying RTEMS_SELF for id results in the event set being sent to the calling task.

The event set to send shall be 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, then it is not present.

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.

CONSTRAINTS:

The following constraints apply to this directive:

  • The directive may be called from within interrupt context.

  • The directive may be called from within device driver initialization context.

  • The directive may be called from within task context.

  • The directive may unblock a task. This may cause the calling task to be preempted.

15.4.2. rtems_event_receive()#

Receives or gets an event set from the calling task.

CALLING SEQUENCE:

rtems_status_code rtems_event_receive(
  rtems_event_set  event_in,
  rtems_option     option_set,
  rtems_interval   ticks,
  rtems_event_set *event_out
);

PARAMETERS:

event_in

This parameter is the event set of interest. Use RTEMS_PENDING_EVENTS to get the pending events.

option_set

This parameter is the option set.

ticks

This parameter is the timeout in clock ticks if the RTEMS_WAIT option is set. Use RTEMS_NO_TIMEOUT to wait potentially forever.

event_out

This parameter is the pointer to an event set. The received or pending events are stored in the referenced event set if the operation was successful.

DESCRIPTION:

This directive can be used to

  • get the pending events of the calling task, or

  • receive events.

To get the pending events use the constant RTEMS_PENDING_EVENTS for the event_in parameter. The pending events are returned to the calling task but the event set of the calling task is left unaltered. The option_set and ticks parameters are ignored in this case. The directive returns immediately and does not block.

To receive events you have to define an input event condition and some options.

The option set specified in option_set is built through a bitwise or of the option constants described below. Not all combinations of options are allowed. Some options are mutually exclusive. If mutually exclusive options are combined, the behaviour is undefined. Options not mentioned below are not evaluated by this directive and have no effect. Default options can be selected by using the RTEMS_DEFAULT_OPTIONS constant. The option set defines

  • if the calling task will wait or poll for the events, and

  • if the calling task wants to receive all or any of the input events.

The calling task can wait or poll for the events.

  • Waiting for events is the default and can be emphasized through the use of the RTEMS_WAIT option. The ticks parameter defines how long the calling task is willing to wait. Use RTEMS_NO_TIMEOUT to wait potentially forever, otherwise set a timeout interval in clock ticks.

  • Not waiting for events (polling) is selected by the RTEMS_NO_WAIT option. If this option is defined, then the ticks parameter is ignored.

The calling task can receive all or any of the input events specified in event_in.

  • Receiving all input events is the default and can be emphasized through the use of the RTEMS_EVENT_ALL option.

  • Receiving any of the input events is selected by the RTEMS_EVENT_ANY option.

RETURN VALUES:

RTEMS_SUCCESSFUL

The requested operation was successful.

RTEMS_INVALID_ADDRESS

The event_out parameter was NULL.

RTEMS_UNSATISFIED

The events of interest were not immediately available.

RTEMS_TIMEOUT

The events of interest were not available within the specified timeout interval.

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.

To receive all events use the event set constant RTEMS_ALL_EVENTS for the event_in parameter. Do not confuse this event set constant with the directive option RTEMS_EVENT_ALL.

A task can receive all of the pending events by calling the directive with a value of RTEMS_ALL_EVENTS for the event_in parameter and the bitwise or of the RTEMS_NO_WAIT and RTEMS_EVENT_ANY options for the option_set parameter. The pending events are returned and the event set of the task is cleared. If no events are pending then the RTEMS_UNSATISFIED status code will be returned.

CONSTRAINTS:

The following constraints apply to this directive:

  • The directive may be called from within device driver initialization context.

  • The directive may be called from within task context.

  • The timeout functionality of the directive requires a clock tick.