RTC not accurate

[William.wei]

hi support team,

i have ESB project for customer, and now i have one fundamental question about RTC cc compare event, i am struggled in this problem.

static __INLINE void radio_rtc_compare0_set(uint32_t value)

{

    RADIO_RTC->CC[0] = value -1;

}

I set the value as 16, so the frequent would be 16/32768 == 488us, and it is true, most case, the event happens in about 488us,

But sometime it would be 520us(just power down and power up the device), I could not figure out the reason for this.  

The consequence for this is that, the frequent for the VR gaming handles would not correct (1/2*520 ==960 HZ). 

After the device reset, the frequent changed, so it is not correct. It happens 20% of the chance after resetting.

The debug pin singal is simple "nrf_gpio_pin_toggle(DATA_SENDING_P1)"  from RADIO_RTC_IRQHandler(void)

any idea or suggestion on this? it would be very helpful.

Thanks in advance!

Regards,

William.

[William.wei]

Hi Jørgen,

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

Regards,

William.

[Jørgen Holmefjord]

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