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How Long Does It Take To Unblock?

Posted by John W. on December 20, 2005

if( xQueueSendFromISR( xRxedCharsU0, &cChar, pdFALSE ) )
/*If the post causes a task to wake force a context switch as the woken task may have a higher priority than the task we have interrupted. */

In task:

for (EVER)

/* Block on the queue that contains received bytes until a byte is
available. */
if( xQueueReceive( xRxedCharsU0, &cByteRxed, comRX_BLOCK_TIME ) )

How long does it take for the task to be unblocked? Is it a function of the timer tick or of the CPU clock?


RE: How Long Does It Take To Unblock?

Posted by Richard on December 20, 2005
In this case the timer tick does not effect the time it takes to unblock as the action occurs in the ISR. Posting to the queue may cause a task to be unblocked and placed in the ready queue. If such a task has a priority higher than the interrupted task then xQueueSendFromISR() will return true and taskYIELD will be called. taskYIELD makes the unblocked task the current task (just a pointer assignment) - meaning that the unblocked task is returned to as the ISR exists. A faster CPU clock will obviously make the function execute faster, but the tick rate is not relevant in this case.


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