Task Notification

1. Chapter 9
Task Notifications

2. 9.1 Chapter Introduction and Scope
• Communicating Through Intermediary Objects

3. 9.1 Chapter Introduction and Scope
• Task Notifications—Direct to Task Communication

4. Scope
• A task’s notification state and notification
value.
• How and when a task notification can be used
in place of a communication object, such as a
semaphore.
• The advantages of using a task notification in
place of a communication object.

5. 9.2 Task Notifications
Benefits and Limitations
• Performance Benefits of Task Notifications
– Faster
• RAM Footprint Benefits of Task Notifications
– Low RAM usage
• Limitations of Task Notifications
– Sending an event or data to an ISR
– Enabling more than one receiving task
– Buffering multiple data items
– Broadcasting to more than one task
– Waiting in the blocked state for a send to complete

6. 9.3 Using Task Notifications
• Event API:
– BaseType_t xTaskNotifyGive( TaskHandle_t xTaskToNotify );
– void vTaskNotifyGiveFromISR(
TaskHandle_t xTaskToNotify,
BaseType_t *pxHigherPriorityTaskWoken);
– uint32_t ulTaskNotifyTake( BaseType_t xClearCountOnExit,
TickType_t xTicksToWait );

7. 9.3 Using Task Notifications

8. 9.3 Using Task Notifications
• Data API:
– BaseType_t xTaskNotify(
– TaskHandle_t xTaskToNotify,
– uint32_t ulValue,
– eNotifyAction eAction );
–
– BaseType_t xTaskNotifyFromISR(
– TaskHandle_t xTaskToNotify,
– uint32_t ulValue,
– eNotifyAction eAction,
– BaseType_t *pxHigherPriorityTaskWoken );

9. About “eNotifyAction”
• eNoAction
– Similar to binary semaphore.
• eSetBits
– Use as group event.
• eIncrement
– Used as a binary or counting semaphore, and is
equivalent to xTaskNotifyGive()
• eSetValueWithoutOverwrite
• eSetValueWithOverwrite

10. 9.3 Using Task Notifications
• BaseType_t xTaskNotifyWait
• ( uint32_t ulBitsToClearOnEntry,
• uint32_t ulBitsToClearOnExit,
• uint32_t *pulNotificationValue,
• TickType_t xTicksToWait );

11. Task Notifications Used in Peripheral
Device Drivers: UART Example
Idle
UART Interrupt
Send Task
Interrupt 1 Interrupt N

12. Task Notifications Used Directly Within an Application