timer drift

RE: timer drift

Tong Yu — Thu, 02 Feb 2017 13:22:01 GMT

OK，thank you very much for the information!

RE: timer drift

Sigurd — Thu, 02 Feb 2017 13:18:03 GMT

The NRF_TIMER2 is based on the HFCLK (16 MHz/ PCLK16M) and have a 62.5 ns resolution. The HFCLK is based on the 64 MHz crystal oscillator (HFXO), which is controlled by the 32 MHz external crystal. See the drawing here.

The 8ppm is the additional HFLCK Frequency tolerance needed when using synthesized clock (not recommended). The HFXO Frequency tolerance is 60ppm, this means that you need a 32 MHz external crystal with at least 60ppm for the radio peripheral to work. On the nRF52-DK the 32 MHz external crystal is 10ppm.

RE: timer drift

Tong Yu — Thu, 02 Feb 2017 12:33:59 GMT

OK, I got it, thanks! But may I ask that if the NRF_TIMER2 is based on the 64 MHz crystal oscillator or not? In the guide, ''sd_clock_hfclk_request()'' is called, but I am not sure it's internal or external. Also, I found out in the infoceter, ''32.768 kHz synthesized from HFCLK (LFSYNT)'' has the lowest ppm which is 8, so that means by using this one I will get the smallest time drift,right?

RE: timer drift

Sigurd — Thu, 02 Feb 2017 12:07:12 GMT

Hi,

Here is an online-calculator you can use to calculate the drift. The formula is: Time Drift in Seconds/Day = ( [ Accuracy in PPM ] / 1 Million ) * ( # Seconds Per Day )

RE: timer drift

Tong Yu — Thu, 02 Feb 2017 11:52:32 GMT

nRF52 DK. I just saw the crystal's ppm on info center(I repaired the link), I am not sure it is guaranteed or not.

RE: timer drift

Roger Clark — Thu, 02 Feb 2017 06:13:59 GMT

What boards are you using. Are your crystals guaranteed to be that accuracy ?