Cannot restart RTC from PPI after STOP, CLEAR tasks

Question

Hi,

I worked on the nrf51 for some years and recently moved over to the nrf52. PPI is a new interface I am exploring. I am having trouble restarting a RTC which was started by the CPU and Stopped by PPI.

If the RTC is started from PPI(say some GPIOTE event assigned to PPI), I have no trouble with the STOP, CLEAR, START task sequence.

If the RTC is first started from the CPU (say in main before the while loop), I use PPI to STOP the RTC, immediately clear the RTC CC0 event, then restart it later with RTC_START using PPI. It does not start, but I do see the counter get cleared. Is there something I am possibly missing?

This is non-soft device by the way. I'm working off the RTC example... although in the future I will introduce the softdevice

Hi,

Instead of using the driver APIs, I tried with just the HAL and still turn up with the same results. I also switched to RTC0 and RTC2... same behavior. Here is the example I am testing

void gpioConfig(void)
{
   
  NRF_GPIOTE->CONFIG[0] = ( (GPIOTE_CONFIG_MODE_Task << GPIOTE_CONFIG_MODE_Pos) | 
                                       (22 << GPIOTE_CONFIG_PSEL_Pos) | 
                  (GPIOTE_CONFIG_POLARITY_Toggle << GPIOTE_CONFIG_POLARITY_Pos) |                                                      
                       (GPIOTE_CONFIG_OUTINIT_High << GPIOTE_CONFIG_POLARITY_Pos) );
    

  
}

static void clock_config(void)
{

    // Recommended by Nordic before using RTC
    // See nRF52832_Rev_2_Errata_v1.0 | 3.3 [20] RTC: Register values are invalid
    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
    NRF_CLOCK->TASKS_LFCLKSTART = 1;
    while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0) {}
    NRF_RTC2->TASKS_STOP = 0;
	
}


static void rtc_config(void)
{

NRF_RTC2->EVTENSET = RTC_EVTENSET_COMPARE0_Enabled <<RTC_EVTENSET_COMPARE0_Pos; 
   
    NRF_RTC2->PRESCALER = 2183;
    NRF_RTC2->CC[0] = 1;

}


static void ppi_config(void)
{
    ret_code_t err_code;
	
    NRF_PPI->CH[0].EEP = (uint32_t) &NRF_RTC2->EVENTS_COMPARE[0];
    NRF_PPI->CH[0].TEP = (uint32_t)&NRF_RTC2->TASKS_STOP;
    NRF_PPI->FORK[0].TEP = (uint32_t)&NRF_RTC2->TASKS_CLEAR;
    NRF_PPI->CHEN |= (PPI_CHEN_CH0_Enabled << PPI_CHEN_CH0_Pos);
    
    NRF_PPI->CH[1].EEP = (uint32_t) &NRF_RTC2->EVENTS_COMPARE[0];
    NRF_PPI->CH[1].TEP = (uint32_t)&NRF_RTC2->TASKS_START;
    NRF_PPI->FORK[1].TEP = (uint32_t)&NRF_GPIOTE->TASKS_OUT[0];  
    NRF_PPI->CHEN |= (PPI_CHEN_CH1_Enabled << PPI_CHEN_CH1_Pos);
    
 
}

int main(void)
{

    NRF_POWER->DCDCEN = 1;                          
    gpioConfig();

    
    rtc_config();
    ppi_config();
   clock_config();
	
   NRF_RTC2->TASKS_START=1;

    while(1)
    {
        __WFE();
    }
}