NRF9160 ticks accuracy

[Sjors Hettinga]

Dear Sir / Madam,

We are testing with NRF9160 and building on top of k_uptime_ticks, I find the precision of the ticks clock to be ~70 ppm, while testing on my desk. According to the specification. https://docs.nordicsemi.com/bundle/ps_nrf9160/page/pmu_oscillators.html, when the LFXO is enabled, it should be +/- 40 ppm.

In the .config file of the application I find CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=y, so the LFXO should be enabled instead of the RC oscillator.

It almost looks like the RC oscillator is driving the k_uptime_ticks instead of the LFXO. Is there a way to verify this?

For the context: The program runs on top of the B0 and MCUBOOT, all having CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=y set.

Kind regards,

Sjors

 

[Hung Bui]

Hi Sjors, 
The 32kHz RC internal oscillator has much lower accuracy than 70ppm (according to spec it's 30%). So I think the chip is using the XTAL already.
Could you give the part number of the crystal and the layout and schematic of the board ?
Could you tell how you measured the accuracy of the ticks?