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Stack size of a Task

Posted by vdhaval on April 6, 2016


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 * configMINIMALSTACKSIZE). The configMINIMALSTACKSIZE macro is set to 128. But when I am setting 'stacksize' to 256 i.e. (2 * configMINIMALSTACKSIZE), 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

Stack size of a Task

Posted by rtel on April 6, 2016

But when I am setting 'stacksize' to 256 i.e. (2 * configMINIMALSTACKSIZE), 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?

Stack size of a Task

Posted by vdhaval on April 6, 2016


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

Stack size of a Task

Posted by rtel on April 6, 2016

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


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.



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