ble time sync among nrf52840 devices high frequecy timer vs rtc

RE: ble time sync among nrf52840 devices high frequecy timer vs rtc

eleven-x_devteam — Thu, 13 Jun 2024 02:33:10 GMT

Hi Audun,

Thanks for the quick reply.

I was testing with my custom boards and F/W and it turned out that there was another sd_clock_hfclk control code for battery and temperature reading and that part was calling "sd_clock_hfclk_release(): so I verified that high frequency timer didn't have that much time drift even after ts_tx_stop() without any other sd_clock_hfclk control code.

Thanks!

RE: ble time sync among nrf52840 devices high frequecy timer vs rtc

Audun — Wed, 12 Jun 2024 11:25:48 GMT

Hi eleven-x_devteam ,

it should come down to the accuracy of the 32 MHz crystal on your board. The nRF5x-DKs typically use a 30 ppm crystal, which when comparing two devices would give you a worst-case drift of 60 ppm (or 60 microseconds per second). Over a two hour period this should still be less than one second, so there seems to be something else going on that affects the drift if you see 14 seconds over this period.

One thing that would significantly affect accuracy is if the high frequency clock source switches from the crystal oscillator to the internal one. The internal one is relatively inaccurate by comparison. However, as long as you dont call ts_disable() or sd_clock_hfclk_release(), the crystal oscillator should still be providing clock for the TIMERs.

Are you using the example code without modification in your testing?

Best regards,

Audun

RE: ble time sync among nrf52840 devices high frequecy timer vs rtc

Sam D — Tue, 11 Jun 2024 12:48:09 GMT

Hi eleven-x_devteam We will look at this asap.