[Task Control]

task. h
BaseType_t xTaskCallApplicationTaskHook( TaskHandle_t xTask, void *pvParameter );

configUSE_APPLICATION_TASK_TAG must be defined as 1 for this function to be available. See the RTOS Configuration documentation for more information.

A ‘tag’ value can be assigned to each task. Normally this value is for the use of the application only and the RTOS kernel does not access it. However, it is possible to use the tag to assign a hook (or callback) function to a task – the hook function being executed by calling xTaskCallApplicationTaskHook(). Each task can define its own callback, or simply not define a callback at all.

Although it is possible to use the first function parameter to call the hook function of any task, the most common use of task hook function is with the trace hook macros, as per the example given below.

Task hook functions must have type TaskHookFunction_t, that is take a void * parameter, and return a value of type BaseType_t. The void * parameter can be used to pass any information into the hook function.

xTask The handle of the task whose hook function is being called. Passing NULL as xTask will call the hook function assocaited with the currently executing task.
pvParameter The value to pass to the hook function. This can be a pointer to a structure, or simply a numeric value.
Example usage:
/* In this example a callback function is being assigned as the task tag. First define the callback function - this must have type TaskHookFunction_t as per this example. */ static BaseType_t prvExampleTaskHook( void * pvParameter ) { /* Perform some action - this could be anything from logging a value, updating the task state, outputting a value, etc. */ return 0; } /* Now define the task that sets prvExampleTaskHook as its hook/tag value. This is in fact registering the task callback, as described on the xTaskCallApplicationTaskHook() documentation page. */ void vAnotherTask( void *pvParameters ) { /* Register our callback function. */ vTaskSetApplicationTaskTag( NULL, prvExampleTaskHook ); for( ;; ) { /* Rest of task code goes here. */ } } /* As an example use of the hook (callback) we can get the RTOS kernel to call the hook function of each task that is being switched out during a reschedule. */ #define traceTASK_SWITCHED_OUT() xTaskCallApplicationTaskHook( pxCurrentTCB, 0 )

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