Task delay faster that expected

[ibrahim upright]

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]

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

[Susheel Nuguru]

perfect answer., +1

[ibrahim upright]

Thank you both for the answer ,

May i have a sample code for the hardware timer and direct task notification??. 

Thanks A lot

ibrahim 

[CheMax]

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<<TIMER_MODE_MODE_Pos;
  NRF_TIMER1->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<<TIMER_INTENSET_COMPARE0_Pos;  
  // Enable timer interupt
  NVIC_ClearPendingIRQ(TIMER1_IRQn);
  NVIC_EnableIRQ(TIMER1_IRQn);
  
  return NRF_SUCCESS;
}
/*--------------------------------------------------------------------------------------*/  
xTaskHandle hSomeTask;
bool CreateSomeTask (uint8_t StackSize, uint8_t Priority)
{
	return xTaskCreate(tSomeTask, "SomeTask", StackSize, NULL, Priority, &hSomeTask);
}
/*--------------------------------------------------------------------------------------*/
void tSomeTask  (void *pvConext)
{
	// Init all what you need
	TimerCreate();	// Create 1min timer
	
	// Task Body
	for(;;)
	{
		// Wait notification
		xTaskNotifyWait(0x00, 0xffff, NULL, portMAX_DELAY);	
		
		/* do something*/
	}
}
/*--------------------------------------------------------------------------------------*/
/* Timer interupt handler */
void TIMER1_IRQHandler(void)
{
  if(NRF_TIMER1->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

[ibrahim upright]

Hi,

Thanks a lot for you answer 

i Have another question why do i need this part in the code : 

volatile uint32_t dummy = NRF_TIMER1->EVENTS_COMPARE[0];
(void)dummy;

Thanks you CheMax