RTC not accurate

RE: RTC not accurate

Jørgen Holmefjord — Thu, 29 Jul 2021 14:33:42 GMT

Hi William,

Yes, it looks like that is correct. I created a sample application that will use PPI+GPIOTE to toggle GPIOs on the TICK and COMPARE0 events from the RTC. The COMPARE0 event will also clear the RTC through a PPI fork.

As you can see from the logic trance, there is a delay between the COMPARE0 event where the RTC is cleared before the first TICK event occurs. This is what is described in the image you posted.

Best regards,
Jørgen

RE: RTC not accurate

William.wei — Tue, 27 Jul 2021 09:01:01 GMT

Hi Jørgen,

is it related to such document in the spec? i am not sure because of this

Regards,

William.

RE: RTC not accurate

William.wei — Tue, 27 Jul 2021 08:16:51 GMT

Which clock source are you using for the LFCLK? LFRC or LFXO?
xtal 32K;
If using LFRC, do you calibrate the LFCLK after powerup and at regular intervals?
Is there any other peripherals running at higher priority that could delay the handling of the RTC event? To get exact timing without being affected by other higher priority peripherals, you can connect the COMPARE event from the RTC to a toggle a GPIO using GPIOTE through PPI.
directly interrupt handler
void RADIO_RTC_IRQHandler(void)
{
if (RADIO_RTC->EVENTS_COMPARE[0] == 1)
{
RADIO_RTC->EVENTS_COMPARE[0] =0; //clear rtc compare event
}
nrf_gpio_pin_toggle(DATA_SENDING_P1);
if(on_radio_rtc_interrupt)
on_radio_rtc_interrupt();
}
Is the delay in RTC event handling consistent for every event, or does it differ after powerup?
no delay in the handler as upper code,sometimes it is correct, sometimes it is not correct, looks like there is one tick delay(randomly) after device resetting.
Are you seeing this on multiple devices, or just one device?
multi DK boards, i believe it is common phenomenon;

Regards,

William.

RE: RTC not accurate

Jørgen Holmefjord — Mon, 26 Jul 2021 10:19:42 GMT

Hi William,

I have some questions that needs clarification:

Which clock source are you using for the LFCLK? LFRC or LFXO?
If using LFRC, do you calibrate the LFCLK after powerup and at regular intervals?
Is there any other peripherals running at higher priority that could delay the handling of the RTC event? To get exact timing without being affected by other higher priority peripherals, you can connect the COMPARE event from the RTC to a toggle a GPIO using GPIOTE through PPI.
Is the delay in RTC event handling consistent for every event, or does it differ after powerup?
Are you seeing this on multiple devices, or just one device?

Best regards,
Jørgen