Generating a pulse with RTC1 and PPI

Question

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 · Accepted Answer

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. } }