The FreeRTOS kernel is now an MIT licensed AWS open source project, and these pages are being updated accordingly.

Quality RTOS & Embedded Software

About Contact Support FAQ Download

Menu

Quick Start

Supported MCUs

PDF Books

Trace Tools

Ecosystem

Quick Start Guide

Support Forum

⇓ Download Source ⇓

FreeRTOS+ Ecosystem

FreeRTOS+TCP:
Thread safe TCP/IP stack

SafeRTOS:
TUV certified RTOS

OpenRTOS:
Commercial Licensed RTOS

Fail Safe File System:
Ensures data integrity

FreeRTOS BSPs:
3rd party driver packages

Trace & Visualisation:
Tracealyzer for FreeRTOS

CLI:
Command line interface

WolfSSL SSL / TLS:
Networking security protocols

RTOS Training:
Delivered online or on-site

IO:
read(), write(), ioctl() interface

FreeRTOS+ Lab Projects

FreeRTOS+POSIX:
POSIX threading API

FreeRTOS+FAT:
Thread aware file system

xTaskCallApplicationTaskHook
[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.

Parameters:

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 )