rtc nrf51 SDK example matches COMPARE0 only once

[i_am_trying]

In order to learn how to use the RTC0 to handle an event every second, I am debugging the rtc SDK example.

Expectation: The rtc example sets the time to check the counter time at 3 seconds. I expect every 3 seconds. the int_type in rtc_handler() will equal NRF_DRV_RTC_INT_COMPARE0.

What I am seeing: the int_type in rtc_handler() equals NRF_DRV_RTC_INT_COMPARE0 after the first three seconds. Then int_type equals only NRF_DRV_RTC_INT_TICK.

Question: is my assumption correct the COMPARE0 should keep repeating such that there is a match every 3 seconds (in this example)

Question: If not, what is the example missing to do so?

thank you.

[Stefan Birnir Sverrisson]

Hi

The internal event handler of the rtc driver, i.e. the nrf_drv_rtc_int_handler, handles the RTC0 peripheral interupt and then calls the registered event handler of the application. If you look into the nrf_drv_rtc_int_handler, you see that interrupts for any COMPARE[x] events are disabled, while TICK and OVERFLOW interrupts are not disabled. If you avoid disabling the COMPARE[x] interrupts, then the COMPARE[0] interrupt will be recurrent after you clear the RTC0 counter. The following code shows the modified nrf_drv_rtc_int_handler where two lines are commented out to enable recurrent COMPARE[x] interrupt:

__STATIC_INLINE void nrf_drv_rtc_int_handler(NRF_RTC_Type * p_reg, uint32_t instance_id)
{
		uint32_t i;
		uint32_t int_mask = (uint32_t)NRF_RTC_INT_COMPARE0_MASK;
		nrf_rtc_event_t event = NRF_RTC_EVENT_COMPARE_0;

		for (i = 0; i < RTC_CHANNEL_NUM; i++)
		{
				if (nrf_rtc_int_is_enabled(p_reg,int_mask) && nrf_rtc_event_pending(p_reg,event))
				{
						//nrf_rtc_event_disable(p_reg,int_mask);
						//nrf_rtc_int_disable(p_reg,int_mask);
						nrf_rtc_event_clear(p_reg,event);
						m_handlers[instance_id]((nrf_drv_rtc_int_type_t)i);
				}
				int_mask <<= 1;
				event    = (nrf_rtc_event_t)((uint32_t)event + sizeof(uint32_t));
		}
		event = NRF_RTC_EVENT_TICK;
		if (nrf_rtc_int_is_enabled(p_reg,NRF_RTC_INT_TICK_MASK) &&
				nrf_rtc_event_pending(p_reg, event))
		{
				nrf_rtc_event_clear(p_reg, event);
				m_handlers[instance_id](NRF_DRV_RTC_INT_TICK);
		}

		event = NRF_RTC_EVENT_OVERFLOW;
		if (nrf_rtc_int_is_enabled(p_reg,NRF_RTC_INT_OVERFLOW_MASK) &&
				nrf_rtc_event_pending(p_reg, event))
		{
				nrf_rtc_event_clear(p_reg,event);
				m_handlers[instance_id](NRF_DRV_RTC_INT_OVERFLOW);
		}
}

so with the above change to the nrf_drv_rtc and your proposed code of clearing the counter (as below code), it should work

static void rtc_handler(nrf_drv_rtc_int_type_t int_type)
{
		if (int_type == NRF_DRV_RTC_INT_COMPARE0)
		{
				nrf_gpio_pin_toggle(COMPARE_EVENT_OUTPUT);
				nrf_drv_rtc_counter_clear(&rtc);
		}
		else if (int_type == NRF_DRV_RTC_INT_TICK)
		{
				nrf_gpio_pin_toggle(TICK_EVENT_OUTPUT);
		}
}

[zhwzh308]

in rtc_handler, after handling COMPARE0 interrupt and clear counter, you may also have to re-enable compare event by calling nrf_drv_rtc_cc_set(&rtc, 0, val, true);. Otherwise it may not be able to interrupt after the first time.