Hi, Why should I call the callback vApplicationGetIdleTaskMemory() when I use static memory allocation ? Thank you Michael

You don’t call it, FreeRTOS calls it, you just have to provide it. The Idle task (and potentially the timer service/RTOS daemon task) is created internally by FreeRTOS when the scheduler is started. The tasks need a task control block and a stack, just like any other task. If you are using dynamic memory allocation then FreeRTOS can just allocate the required memory from the heap. If you have opted to use static memory allocation then FreeRTOS cannot obtain the memory itself so you must provide it. That is what the callback/hook function does: https://www.freertos.org/a00110.html#configSUPPORTSTATICALLOCATION