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KERNEL

xTaskNotifyAndQuery / xTaskNotifyAndQueryIndexed
[RTOS Task Notification API]


task.h

 BaseType_t xTaskNotifyAndQuery( TaskHandle_t xTaskToNotify,
                                 uint32_t ulValue,
                                 eNotifyAction eAction,
                                 uint32_t *pulPreviousNotifyValue );
 
BaseType_t xTaskNotifyAndQueryIndexed( TaskHandle_t xTaskToNotify, UBaseType_t uxIndexToNotify, uint32_t ulValue, eNotifyAction eAction, uint32_t *pulPreviousNotifyValue );

See RTOS Task Notifications for more details.

xTaskNotifyAndQueryIndexed() performs the same operation as xTaskNotifyIndexed() with the addition that it also returns the target task’s prior notification value (the notification value at the time the function is called rather than when the function returns) in the additional pulPreviousNotifyValue parameter.

xTaskNotifyAndQuery() performs the same operation as xTaskNotify() with the addition that it also returns the target task’s prior notification value (the notification value as it was at the time the function is called, rather than when the function returns) in the additional pulPreviousNotifyValue parameter.

This function must not be called from an interrupt service routine (ISR). Use xTaskNotifyAndQueryFromISR() instead.

Parameters:
xTaskToNotify   The handle of the RTOS task being notified. This is the target 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.

uxIndexToNotify   The index within the target task’s array of notification values to which the notification is to be sent.

uxIndexToNotify must be less than configTASK_NOTIFICATION_ARRAY_ENTRIES.

ulValue   Used to update the notification value of the target task. See the description of the eAction parameter below.
eAction   An enumerated type that can take one of the values documented in the table below in order to perform the associated action.
pulPreviousNotifyValue   Can be used to pass out the target task’s notification value before any bits are modified by the action of xTaskNotifyAndQuery().

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 xTaskNotifyAndQuery().

eAction Setting Action Performed
eNoAction The target task receives the event, but its notification value is not updated. In this case ulValue is not used.

eSetBits The notification value of the target task will be bitwise ORed with ulValue. For example, if ulValue is set to 0x01, then bit 0 will get set within the target task’s notification value. Likewise if ulValue is 0x04 then bit 2 will get set in the target task’s notification value. In this way the RTOS task notification mechanism can be used as a light weight alternative to an event group.

eIncrement The notification value of the target task will be incremented by one, making the call to xTaskNotify() equivalent to a call to xTaskNotifyGive(). In this case ulValue is not used.
eSetValueWithOverwrite The notification value of the target task is unconditionally set to ulValue. In this way the RTOS task notification mechanism is being used as a light weight alternative to xQueueOverwrite().
eSetValueWithoutOverwrite If the target task does not already have a notification pending then its notification value will be set to ulValue.

If the target 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.

Returns:
pdPASS is returned in all cases other than when eAction is set to eSetValueWithoutOverwrite and the target task’s notification value cannot be updated because the target task already had a notification pending.


Example usage:


uint32_t ulPreviousValue;

/* Set bit 8 in the 0th notification value of the task referenced
by xTask1Handle. Store the task’s previous 0th notification
value (before bit 8 is set) in ulPreviousValue. */

xTaskNotifyAndQueryIndexed( xTask1Handle,
0,
( 1UL << 8UL ),
eSetBits,
&ulPreviousValue );

/* Send a notification to the task referenced by xTask2Handle,
potentially removing the task from the Blocked state, but without
updating the task’s notification value. Store the tasks notification
value in ulPreviousValue. */

xTaskNotifyAndQuery( xTask2Handle, 0, eNoAction, &ulPreviousValue );

/* Set the notification value of the task referenced by xTask3Handle
to 0x50, even if the task had not read its previous notification value.
The task’s previous notification value is of no interest so the last
parameter is set to NULL. */

xTaskNotifyAndQuery( xTask3Handle, 0x50, eSetValueWithOverwrite, NULL );

/* Set the notification value of the task referenced by xTask4Handle
to 0xfff,
but only if to do so would not overwrite the task’s existing notification
value before the task had obtained it (by a call to xTaskNotifyWait()
or ulTaskNotifyTake()). The task’s previous notification value is saved
in ulPreviousValue. */

if( xTaskNotifyAndQuery( xTask4Handle,
0xfff,
eSetValueWithoutOverwrite,
&ulPreviousValue ) == pdPASS )
{
/* The task’s notification value was updated. */
}
else
{
/* The task’s notification value was not updated. */
}





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