take & give semaphore

Kernel
1

wella wrote on Thursday, 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

2

rtel wrote on Friday, 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.

3

wella wrote on Friday, 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 :frowning: … I would be glad if something like MicroC/OS-II was written about FRT.

BR
Martin