Stack size of a Task

vdhaval wrote on Wednesday, April 06, 2016:

Hi,

I am using FreeRTOS with STM32L4xx MCU. I am creating a task following way:

  /* Create the thread(s) */
  /* definition and creation of defaultTask */
  osThreadDef(defaultTask, StartDefaultTask, osPriorityNormal, 0, stacksize);
  defaultTaskHandle = osThreadCreate(osThread(defaultTask), NULL);

Here ther ‘stacksize’ is set to 512 i.e. (4 * configMINIMAL_STACK_SIZE). The configMINIMAL_STACK_SIZE macro is set to 128. But when I am setting ‘stacksize’ to 256 i.e. (2 * configMINIMAL_STACK_SIZE), it is not working properly.

Now to measure the requirement of stack for that task I called “uxTaskGetStackHighWaterMark()” within that task at two places, first at the beginning of the task and second after calling few functions from the task. The first call returns 0 and the second call returns 0x1E4. And that means around 484 words of stack is still free!!

Then why am I not able to reduce the stack size to 256 or to 128?

Appreciate your quick help.

Thanks,
Dhaval

rtel wrote on Wednesday, April 06, 2016:

But when I am setting ‘stacksize’ to 256 i.e. (2 * configMINIMAL_STACK_SIZE), it is not working properly.

What is not working? The task can’t be created, the task never starts, you get a stack overflow, the code doesn’t compile, the chip gets too hot, what?

vdhaval wrote on Wednesday, April 06, 2016:

Hi,

Thanks for your quick reply.

So, immediately after creating the thread as mentioned in my previous message from main() function, I am starting scheduler by calling “osKernelStart()” and then there is a ‘while(1)’ loop in the main() function. It should never reach to that ‘while(1)’ loop if things are working fine as the control is now taken by the Scheduler. But actually it reaches there!! So it comes out of the thread.

Regards,
Dhaval

rtel wrote on Wednesday, April 06, 2016:

If you had stated that originally then you would have had your answer
straight away, and I would have saved some valuable time.

http://www.freertos.org/FAQ-how-to-use-the-FreeRTOS-support-forum.html

osKernelStart() is not a FreeRTOS function, but assuming it just calls
vTaskStartScheduler(), then you don’t have enough heap space remaining
to create the Idle (and depending if configUSE_TIMERS is set to 1) the
timer service tasks.

I think all the examples we provide give this information in a comment
after the call to vTaskStartScheduler(), which is where your code will
have ended up.

http://www.freertos.org/a00111.html

Regards.