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Precious time delay for all tasks

Posted by Samuel on October 29, 2011
I have some function require precious time delay, it maybe at any task with different priority. I am not sure how to do it properly in RTOS.

For example I need a 100mS pulse, the code as below:

PintA_Output_High;
vTaskDelay( 10_Ticks); // 100 mS delay.
PintA_Outpou_Low;

If those code in low priority task, the pulse will be longer than 100mS, because after "vTaskDelay( 10_Ticks)" the CPU may execute other higher priority tasks.

RE: Precious time delay for all tasks

Posted by Richard Damon on October 29, 2011
If it is very important that it be not delayed, then it needs to be a top priority task.

Note that there is already some variation built into the program, as a 10 tick delay (unless just after another delay) can be as short as just above 9 ticks, as the remainder of the current tick is the first tick of delay, no matter how much or little of it left.

If you really need an accurate pulse, and the software methods aren't doing well enough, you may need to switch to a dedicated timer, which you can start at just the right point in time, and tells you when to stop and just the right point in time.


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