Problem with timeout

gary10es wrote on Wednesday, December 09, 2009:

Hello everybody,  i have a problem when i use the timeout in a semaphore.

I use EVK1100(AVR 32), freertos 1mseg tick, and i have written this code

if( xSemaphoreTake(xSemaphoreReceived,1) == pdTRUE )

I have measured this time Timeout and it’s variable, never 1 mili second that i want.The obtained values  are 600microsecond, 400microsecond , 768microsecond

anybody can help me?


richard_damon wrote on Wednesday, December 09, 2009:

A 1 ms tic rate means delays are only accurate to 1ms, and in fact, the way FreeRTOS works, the time out will expire in no more than the specified time, so a 1ms delay is 0-1ms, a 2 ms delay is 1-2ms, and so on. (The task may not start immediately on that next tick if some higher priority task is running).

basically time steps in 1 ms intervals, so by its measure anything in “tick 10” is 1 tick before anything in “tick 11”, so a 1 tick delay means until the next tick, which might be almost a full tick in time if the interrupt just happended and might be almost no time if the tick interrupt is about ready to happen.

gary10es wrote on Wednesday, December 09, 2009:

thank you very much