32.768 Crystal routing to P0.10

Question

We need to route P0.00 - P0.01 crystal clock to P0.10 
 Is there a way to do that?

hmolesworth · Accepted Answer

I don't have a tested DPPI option to hand for the nRF5340; here is a tested PPI example for the nRF52832/nRF52840 with a guess at a working nRF5340 DPPI:

#define FCLK_PIN 10  // P0.10
void TestFCLK(void)
{
   // Output the 32.768kHz crystal using h/w toggle on FCLK_PIN - will show as 16.384kHz
   nrf_gpio_cfg_output(FCLK_PIN);
   // Select 32kHz clock source
   NRF_CLOCK->LFCLKSRC = CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos;
   // Start 32.768kHz clock
   NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
   NRF_CLOCK->TASKS_LFCLKSTART = 1;
   while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0) ;
   // Clear started event otherwise won't sleep
   NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
   // Start RTC, enable TICK event
   NRF_RTC0->EVTENSET = RTC_EVTENSET_TICK_Msk;
   NRF_RTC0->TASKS_START = 1;
   // Configure GPIOTE to control output pin
   NRF_GPIOTE->CONFIG[0] = GPIOTE_CONFIG_MODE_Task << GPIOTE_CONFIG_MODE_Pos | GPIOTE_CONFIG_POLARITY_Toggle << GPIOTE_CONFIG_POLARITY_Pos | FCLK_PIN << GPIOTE_CONFIG_PSEL_Pos;
#if 1 // nRF52832
   // Connect TICK event of the RTC to the output pin using PPI and GPIOTE, toggle so 32768/2=16384Hz expected
   NRF_PPI->CH[0].EEP = (uint32_t)&NRF_RTC0->EVENTS_TICK;
   NRF_PPI->CH[0].TEP = (uint32_t)&NRF_GPIOTE->TASKS_OUT[0];
   NRF_PPI->CHEN = PPI_CHEN_CH0_Msk;
#else // nRF5340 - not tested
   // Connect TICK event of the RTC to the output pin using DPPI and GPIOTE, toggle so 32768/2=16384Hz expected
   NRF_RTC0->PUBLISH_TICK       = (DPPI_PUB_CHIDX_Ch0) | (DPPI_PUB_EN_Msk);
   NRF_GPIOTE->SUBSCRIBE_OUT[0] = (DPPI_SUB_CHIDX_Ch0) | (DPPI_SUB_EN_Msk);
   NRF_DPPIC->CHENSET           = (DPPI_CHENSET_CH0_Set << DPPI_CHENSET_CH0_Pos);
#endif
}

Edit: This using-the-dppi-on-the-nrf5340-gpio-toggling might be a useful guide

32.768 Crystal routing to P0.10

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