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xTaskAbortDelay not updating pxPreviousWakeTime

Posted by nelsonpina on December 13, 2016

Hi,

I was using the xTaskAbortDelay call to unblock a task that was previously set to sleep, but I realised that this call is not updating the value of the pxPreviousWakeTime, which causes problems because the next time the task calls the vTaskDelayUntil the following conditions is not using correct information and will assume the tick overflowed:

if( xConstTickCount < *pxPreviousWakeTime ) {..}

Is there anything I'm missing here, or this is the expected behaviour? __ nelson


xTaskAbortDelay not updating pxPreviousWakeTime

Posted by rtel on December 13, 2016

*pxPreviousWakeTime is set to the time at which the task would have unblocked if the delay had not been aborted. That allows vTaskDelayUntil() to be used to unblock the task with an otherwise (non aborted) fixed frequency. That could have been implemented the other way too, but if you need xPreviousWakeTime to be set to the time the task unblocked because the delay was aborted then you have the option of setting xPreviousWakeTime manually after the call to vTaskDelayUntil() returns.


xTaskAbortDelay not updating pxPreviousWakeTime

Posted by nelsonpina on December 13, 2016

Sure, that's the workaround I'm using, setting it manually.

But it's not explicit in the documentation that this is the expected behaviour. The statement I found regarding the pxPreviousWakeTime is:

"Pointer to a variable that holds the time at which the task was last unblocked. The variable must be initialized with the current time prior to its first use (see the example below). Following this, the variable is automatically updated within vTaskDelayUntil()."

With this statement, my understanding was that I would never need to update this variable manually. It would always be properlly managed by the FreeRTOS calls.

Maybe some clarification about this on the xTaskAbortDelay API documentation would be helpful don't you think?

cheers, nelson


xTaskAbortDelay not updating pxPreviousWakeTime

Posted by rtel on December 13, 2016

Yes - the documentation can be updated to note the behaviour.


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