task.h
BaseType_t xTaskNotifyAndQueryFromISR(
TaskHandle_t xTaskToNotify,
uint32_t ulValue,
eNotifyAction eAction,
uint32_t *pulPreviousNotifyValue,
BaseType_t *pxHigherPriorityTaskWoken );
[If you are using RTOS task notifications to implement binary or counting
semaphore type behaviour then use the simpler
vTaskNotifyGiveFromISR() API
function instead of xTaskNotifyAndQueryFromISR().]
xTaskNotifyAndQuery() is similar to xTaskNotify(),
but contains an additional parameter in which the subject task's previous notification
value is returned. xTaskNotifyAndQueryFromISR() is a version of xTaskNotifyAndQuery()
that can be called from an interrupt service routine (ISR).
Each RTOS task has a 32-bit notification value which is initialised to
zero when the RTOS task is created. xTaskNotifyAndQueryFromISR() is used to send an event
directly to and potentially unblock an RTOS task, and optionally update the
receiving task's notification value in one of the following ways:
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Write a 32-bit number to the notification value
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Add one (increment) the notification value
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Set one or more bits in the notification value
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Leave the notification value unchanged
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Parameters:
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xTaskToNotify
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The handle of the RTOS task being notified. This is the subject task.
To obtain a task's handle create the task using
xTaskCreate() and make use of the
pxCreatedTask parameter, or create the task using
xTaskCreateStatic()
and store the returned value, or use the task's name in a
call to xTaskGetHandle().
The handle of the currently executing RTOS task is returned by
the xTaskGetCurrentTaskHandle()
API function.
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ulValue
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Used to update the notification value of the subject task.
See the description of the eAction parameter below.
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eAction
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An enumerated type that can take one of the values documented
in the table below in order to perform the associated action.
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pulPreviousNotifyValue
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Can be used to pass out the subject task's notification value before any
bits are modified by the action of xTaskNotifyAndQueryFromISR().
pulPreviousNotifyValue is an optional parameter, and can be set
to NULL if it is not required. If pulPreviousNotifyValue is not
used then consider using xTaskNotify()
in place of xTaskNotifyAndQueryFromISR().
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pxHigherPriorityTaskWoken
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*pxHigherPriorityTaskWoken must be initialised to pdFALSE (0).
xTaskNotifyAndQueryFromISR() will set *pxHigherPriorityTaskWoken
to pdTRUE if sending the notification caused a task to unblock,
and the unblocked task has a priority higher than the currently
running task.
If xTaskNotifyAndQueryFromISR() sets this value to pdTRUE
then a context switch should be requested before the interrupt
is exited. See the example below.
pxHigherPriorityTaskWoken is an optional parameter and can
be set to NULL.
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eAction Setting
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Action Performed
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eNoAction
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The subject task receives the event, but its
notification value is not updated.
In this case ulValue is not used.
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eSetBits
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The notification value of the subject task will
be bitwise ORed with ulValue. For example, if
ulValue is set to 0x01, then bit 0 will get set
within the subject task's notification value.
Likewise if ulValue is 0x04 then bit 2 will get
set in the subject task's notification value.
In this way the RTOS task notification mechanism can be used
as a light weight alternative to an
event group.
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eIncrement
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The notification value of the subject task will
be incremented by one, making the call to xTaskNotify()
equivalent to a call to xTaskNotifyGive().
In this case ulValue is not used.
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eSetValueWithOverwrite
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The notification value of the subject task is
unconditionally set to ulValue. In this way the
RTOS task notification mechanism is being used as a light
weight alternative to xQueueOverwrite().
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eSetValueWithoutOverwrite
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If the subject task does not already have a
notification pending then its notification value
will be set to ulValue.
If the subject task already has a notification
pending then its notification value is not
updated as to do so would overwrite the previous
value before it was used. In this case the call
to xTaskNotify() fails and pdFALSE is returned.
In this way the RTOS task notification mechanism
is being used as a light weight alternative to
xQueueSend() on a
queue of length 1.
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-
Returns:
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pdPASS is returned in all cases other than when eAction is set to
eSetValueWithoutOverwrite and the subject task's notification value
cannot be updated because the subject task already had a notification
pending.
Example usage:
void vAnISR( void )
{
BaseType_t xHigherPriorityTaskWoken = pdFALSE. /* Muse be Initialised to pdFALSE! */
uint32_t ulPreviousValue;
/* Set bit 8 in the notification value of the task referenced by xTask1Handle.
Store the task's previous notification value (before bit 8 is set) in
ulPreviousValue. */
xTaskNotifyAndQueryFromISR( xTask1Handle,
( 1UL << 8UL ),
eSetBits,
&ulPreviousValue,
&xHigherPriorityTaskWoken );
/* The task's previous notification value is saved in ulPreviousValue. */
/* If the task referenced by xTask1Handle was in the Blocked state, waiting
for the notification, then it will now have been moved from the Blocked
state to the Ready state. If its priority is higher than the priority of
the currently executing task (the task this interrupt interrupted) then
xHigherPriorityTaskWoken will have been set to pdTRUE, and passing the
variable into a call to portYIELD_FROM_ISR() will result in the interrupt
returning directly to the unblocked task. If xHigherPriorityTaskWoken is
still pdFALSE then passing it into portYIELD_FROM_ISR() will have no
effect. */
portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
}
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