FreeRTOS task notification review

One 、 Basic concepts

• effect ： Reduce RAM Consume , Do not create semaphores separately , queue , The task notification can be used automatically after the task is created by the communication mechanism such as counting quantity .
• Default FreeRTOSConfig.h
  configUSE_TASK_NOTIFICATIONS Set to 1, Its FreeRTOS The default is for 1 Of , So task notification is enabled by default .
• FreeRTOS from V8.2.0 The version starts to provide task notification , Each task has a 32 Notification value of bit , in the majority of cases , Task notifications can replace binary semaphores 、 Count the semaphore 、 Event group , It can also be replaced The length is 1 Queues （ You can save a
  32 Bit integer or pointer value ）.
• according to FreeRTOS Official statement , Use task notification rather than through semaphores, etc ICP The task of unblocking the communication mode should be fast 45%, And more economical RAM Memory space

shortcoming ：

• Only one task can receive notification messages , Because you must specify a task to receive notifications .
• Only tasks waiting for notification can be blocked , The task of sending notifications , In any case, it will not enter the blocking state due to transmission failure .

Two 、 experiment

The principle is the same as that of the previous event group 、 Semaphore 、 The message queue communication mechanism is similar , Calling function is different .