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xTaskRestart() revisited

Posted by westmorelandeng on February 17, 2016

Hello Richard,

You had made this comment - wondering if it was looked into or not:

Please add your request to the feature request tracker in sourceforge. It might be possible for the kernel to call xTaskCreate() on the task again, effectively setting it back to its initial conditions using the same TCB and stack. Regards.

I have a need for something like this - to be able to 'reset' or 'restart' a task. I suppose I could kill it and recreate it - but it would be convenient to restart it.

Thanks, John W.

xTaskRestart() revisited

Posted by rtel on February 17, 2016

This has not been done yet as it is actually quite complex - although the new ability to create tasks using statically allocated memory may make it simpler.

xTaskRestart() revisited

Posted by westmorelandeng on February 17, 2016

Hmmm. OK. I was thinking about just saving off the TCB and orig stack and restoring it - maybe it isn't that easy.

Could a region be defined in heap5.c for a particular task to make this easier?

xTaskRestart() revisited

Posted by westmorelandeng on February 18, 2016

Richard,   Do you have a procedure for how to try this with the statically allocated tasks? Maybe the easiest is to 2X the memory at task creation and restore the TCB and stack at exit if the task is to be reset or just rerun the task creation steps at exit using the original TCB and stack pointers.

Thanks,   John

xTaskRestart() revisited

Posted by rtel on February 18, 2016

I don't think this can be done in a portable way very easily. To truly restart a task (so you get the parameter passed in again, the thread local storage was cleared, etc.) you would need an API function that:

1) Deletes the existing task to ensure it is not referenced from any state lists or other objects. The easiest way of doing that would be to call vTaskDelete().

2) Create a new task so the TCB was re-initialised, the initial stack of the task was set back to its original state, the register values were set back to their initial state, etc. The easiest way of doing that would be to call xTaskCreate() again - however you would not know what the initial value of the task parameter was.

With dynamically allocated memory this is tricky because once the task has been deleted there is no stack, so xTaskCreate() could not be called. However, with statically allocated memory that is not the case, the stack memory can be borrowed between the delete and subsequent re-creation of the task.

In fact, probably the easiest way of doing this would be to allow the RTOS daemon task/timer service task to perform these actions, rather than have the task do it itself. That way you could also do it with dynamic memory allocation.

However, maybe if you really want a task to restart the simplest thing to do would be to have the task jump back up to the start of its implementing function at the appropriate time? You would have to re-initialise any stack variables manually, as the function prologue code would not execute.

xTaskRestart() revisited

Posted by westmorelandeng on February 18, 2016

Richard, So, maybe a taskReset 'hook' can be added?

Thanks, John W.

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