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.
/* 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. */
/* 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
#define traceTASK_SWITCHED_OUT() xTaskCallApplicationTaskHook( pxCurrentTCB, 0 )
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