Generating a pulse with RTC1 and PPI

[Florin]

Hi there,

I am trying to generate a pulse on a pin using RTC1 and PPI. Using a TIMER this works fine but my goal is to incur minimum current consumption by using only the LFCLK. Here's my code:

  NRF_RTC1->TASKS_STOP = 1;
  NRF_RTC1->TASKS_CLEAR = 1;               // clear the task first to be usable for later

  NRF_RTC1->PRESCALER = 32; //1kHz
  NRF_RTC1->CC[0] = 1000;  //1s interval
  NRF_RTC1->EVTENSET = RTC_EVTENSET_COMPARE0_Msk;

  uint8_t ch_num = 0;
  nrf_gpiote_task_config(ch_num, PIN_NO, NRF_GPIOTE_POLARITY_TOGGLE, NRF_GPIOTE_INITIAL_VALUE_HIGH);
  NRF_PPI->CH[ch_num].EEP = (uint32_t)&NRF_RTC1->EVENTS_COMPARE[0];
  NRF_PPI->CH[ch_num].TEP = (uint32_t) &NRF_GPIOTE->TASKS_OUT[ch_num];
  NRF_PPI->CHEN = 1 << ch_num;

  NRF_RTC1->TASKS_START = 1;
  ...
  __WFI();

This code will make the PIN_NO stay high (because of the NRF_GPIOTE_INITIAL_VALUE_HIGH) for 1s then low indefinitely. I guess this is because the EVENTS_COMPARE[0] is never reset to 0.

Is there a way to make this work? Thanks! florin

[Susheel Nuguru]

you are using GPIOTE module, this uses HFCLK

[Susheel Nuguru]

void RTC1_IRQHandler(void)
{ 
  static volatile bool pin_state_high = true:

  if ( (NRF_RTC1->EVENTS_COMPARE[0] == 1) &&
      ((NRF_RTC1->INTENCLR & (1 << RTC_INTENCLR_COMPARE0_Pos)) != 0 ) )
	{
		NRF_RTC1->TASKS_CLEAR = 1;
		NRF_RTC1->EVENTS_COMPARE[0] = 0;

            if(pin_state_high)
            {
               NRF_GPIO->OUTCLR = (1 << PIN_NO);
            }
            else
            {
               NRF_GPIO->OUTSET = (1 << PIN_NO);
            }
            pin_state_high = !pin_state_high;
	}
}

/**
 * @brief Function for application main entry.
 */
int main(void)
{
	
	NRF_CLOCK->LFCLKSRC            = (CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos);
    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
    NRF_CLOCK->TASKS_LFCLKSTART    = 1;

    while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0)
    {
        // Do nothing.
    }
		
  NRF_RTC1->TASKS_STOP = 1;
  NRF_RTC1->TASKS_CLEAR = 1;               // clear the task first to be usable for later

  NRF_RTC1->PRESCALER = 32; //1kHz
  NRF_RTC1->CC[0] = 1000;  //1s interval
  NRF_RTC1->EVTENSET = RTC_EVTENSET_COMPARE0_Msk;
  NRF_RTC1->INTENSET = RTC_INTENSET_COMPARE0_Msk;
  NVIC_ClearPendingIRQ(RTC1_IRQn);
  NVIC_EnableIRQ(RTC1_IRQn);
  NRF_RTC1->TASKS_START = 1;

  nrf_gpio_set_dir_as_output_something (API not top of my head)

    while (true)
    {
        __SEV();
	    __WFE();

	    __WFE();            
        // Do Nothing - GPIO can be toggled without software intervention.
    }
}

[Florin]

Thanks Aryan for the quick answer, now it works.

So I guess that there's no way to avoid using RTC1_IRQHandler. A similar solution using TIMER1 doesn't require IRQ handling.

Cheers!

[Susheel Nuguru]

i think you can use timer as you are using gpiote anyways that uses HFCLK.

[Florin]

I see. Is there actually any way to generate such pulse using less power than the method above?