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take & give semaphore

Posted by Martin Velek on December 11, 2008
Hello,

is there a simple way, how to achieve this functionality?

void interrupt_handler_timer_A(void)
{
xSemaphoreGiveFromISROnlyIfSemaphoreWasTakenBefore(xSemaphore);
}

void TaskA(...)
{
startTimerA();
stopTimerA();
xSemaphoreTake(xSemaphore);
exit(1); // we should never get here

}

I mean that the interrupt handler can give semaphore only if was taken before. In other cases it skips it.

Thank you for help

Martin

RE: take & give semaphore

Posted by Richard on December 12, 2008
You could do something like this:

if( xQueueIsQueueEmptyFromISR( (xQueueHandle) xSemaphore )
{
____xSemaphoreGiveFromISR( xSemaphore );
}

be careful of race conditions though.

I don't understand the comment "// we should never get here" in your sample task code. It looks like you would get there as soon as the semaphore was available.

Regards.

RE: take & give semaphore

Posted by Martin Velek on December 12, 2008
Hi Richard,

thank you for answer. The comment "// we should never get here" means, that by function stopTimerA() disables generating Timer interrupt.

Amazing function xQueueIsQueueEmptyFromISR. Exactly what I need. I didn't find it in documentation :( ... I would be glad if something like MicroC/OS-II was written about FRT.

BR
Martin


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