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Posted by rrrum on March 2, 2016


In many examples I see "portENDSWITCHINGISR( xHigherPriorityTaskWoken );" placed as a last line of interrupt routine. This is not always straightforward. In some more complex interrupt handler user may want to put

xSemaphoreGiveFromISR( xSemaphoreMODBUSprocess, &xHigherPriorityTaskWoken );

in some function, maybe after that call some other functions before exiting handler.

So the question is can I put "portENDSWITCHINGISR( xHigherPriorityTaskWoken );" after xSemaphore... but not as a last line of handler. Will it work as intended?



Posted by rtel on March 2, 2016


Will it work as intended?

Depends on which port you are using.


Posted by rrrum on March 3, 2016

I don't understand your answer, can you elaborate more.

I am using CORTEX M4 port of XMC on GCC.

here is my function

~~~~ void syssemsignalisr(syssemt *sem) { portBASETYPE xHigherPriorityTaskWoken = pdFALSE;

xSemaphoreGiveFromISR(*sem, &xHigherPriorityTaskWoken );
portEND_SWITCHING_ISR( xHigherPriorityTaskWoken );


~~~~ which is used as folowing handler

~~~~ void ETH00IRQHandler(void) { uint32_t status;

status = XMCETHMACGetEventStatus(&ethmac);

if (status & XMCETHMACEVENTRECEIVE) { syssemsignalisr(&ethrx_semaphore); }

XMCETHMACClearEventStatus(&ethmac, status); }



Posted by rtel on March 3, 2016

I don't understand your answer, can you elaborate more.

I said "Depends on which port you are using." because, the answer to your question depends on which port you are using, and as you didn't say, I couldn't answer the question.

If you are using a Cortex-M4 port then you can call portENDSWITCHINGISR or portYIELDFROMISR at any time - it does not have to be at the end of the ISR.


Posted by richard_damon on March 4, 2016

If I remember right, on the M4 the portYIELDFROMISR triggers a lowest priority interrupt to cause the task switch, which will be blocked by the current ISR running, so exactly when that interrupt is triggered doesn't matter.

On the other hand, in the PIC24 port, the portYIELDFROMISR actually does the task switch, and continues execution at that task, and the code that follows isn't executed until the original task gets switched back to, so it really does need to be the very last code in the ISR.

If you wanted to write you ISR so it can work on system like the latter, then any function that the ISR calls which might set the HigherPriorityTaskWasWoken flag, needs to be passed the flag so it can pass that to the API, and the ISR tests it as its last step.

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