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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