Timer1 NRF_TIMER1-CC[1] not having an effect

Question

I am using the nRF51-DK and have Timer1 setup as follows:

void start_timer(void)
{		
  NRF_TIMER1->MODE = TIMER_MODE_MODE_Timer;  
  NRF_TIMER1->TASKS_CLEAR = 1;       
  NRF_TIMER1->PRESCALER = 4; 
  NRF_TIMER1->BITMODE = TIMER_BITMODE_BITMODE_16Bit;
  NRF_TIMER1->CC[1] = 1000;
		
  // Enable interrupt on Timer 2, both for CC[0] and CC[1] compare match events
  NRF_TIMER1->INTENSET = (TIMER_INTENSET_COMPARE1_Enabled << TIMER_INTENSET_COMPARE1_Pos);

  NVIC_EnableIRQ(TIMER1_IRQn);
		
  NRF_TIMER1->TASKS_START = 1;               // Start TIMER1
}
		

void TIMER1_IRQHandler(void)
{
	if (NRF_TIMER1->EVENTS_COMPARE[1] && 
          NRF_TIMER1->INTENSET & TIMER_INTENSET_COMPARE1_Msk) {

  
    //Clear compare register event	
    NRF_TIMER1->EVENTS_COMPARE[1] = 0;

    if(nrf_gpio_pin_read(21)) {
      nrf_gpio_pin_clear(21);
    }
    else {
      nrf_gpio_pin_set(21);
    }
           
  }
}

I have an oscilloscope connected to pin 21, and am finding that no matter what I set to NRF_TIMER1->CC[1], the pulse width remains the same.

I am also finding that for NRF_TIMER1->PRESCALER set to 0, I am getting a pulse of period ~8 ms. That seems incorrect. Again, NRF_TIMER1->CC[1] has no effect.

Overall I think I am not setting up the timer correctly. I'd appreciate any help with this.

I am using this code with SoftDevice S110.

(Please note that I don't want to use the nrf_drv_timer methods as I find them to be confusing, and would rather use the registers so I can understand the feature consistent with the data sheet.)

Thanks

Susheel Nuguru · Accepted Answer

you have the enable the SHORT that clears the the TIMER value after CC[0] event is triggered. Else no matter what you set in CC register, the timer will go circular over 16bit CC register

Timer1 NRF_TIMER1->CC[1] not having an effect

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