Task delay faster that expected

Question

Hi, 
 I am using nRF52832, SDK 15. My code is based on the freeRTOS code examples. 
 
 I am trying to Run my Task Every 10 ms. I tried to test this by using a counter to print every minute. And every minute ,the notification appears after 58.6 seconds. 
 To Run my Task i am using this function vTaskDelayUntil(&LastWakeTime, pdMS_TO_TICKS(10)); the variable LastWakeTime is been initialized with LastWakeTime = xTaskGetTickCount(); 
 It seemed that the Delay for 10.24 (10) ticks (10 ms) could it cause system clock to be faster ? 
 If i will change the configTICK_RATE_HZ to a round number (2000 for example) would it have any performance downside? (not being a power of 2) and would it solve this?

Thanks A lot 
 ibrahim

CheMax · Accepted Answer

This is a very simplified example written in a couple of minutes. But it shows the necessary basic functions. /*--------------------------------------------------------------------------------------*/ bool TimerCreate (void) { NRF_TIMER1->MODE = TIMER_MODE_MODE_Timer<BITMODE = TIMER_BITMODE_BITMODE_32Bit; NRF_TIMER1->PRESCALER = 0x09; // 16 MHz / 2^9 = 31.25 kHz NRF_TIMER1->CC[0] = 60*31250; // 60 sec = 1 min NRF_TIMER1->INTENSET = TIMER_INTENSET_COMPARE0_Enabled<EVENTS_COMPARE[0]) { // Clear IRQ event flag NRF_TIMER1->EVENTS_COMPARE[0] = 0x0UL; volatile uint32_t dummy = NRF_TIMER1->EVENTS_COMPARE[0]; (void)dummy; // Give Notification xTaskNotifyFromISR(hSomeTask); } } /*--------------------------------------------------------------------------------------*/ Best regards, Max

CheMax · Answer

Hi, 
 I guess the problem will remain. The fact is that the RTS is used to clock the core of the RTOS. There is no possibility to choose a divider so that it gives 1ms. 
 Currently divide 32 is used (if you look at the documentation, the divisor is given as a power of 2). 37768 Hz / 32 = 1024 Hz 
 Therefore, a context switch every 1000/1024 = 0.976 ms. From here and there is an error while waiting. 
 If you need precisely deterministic delays, you can use the hardware timer and direct task notification . 
 
 Regards, 
 Max

Task delay faster that expected

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