Unstable Distance Measurement with Synthesized LFCLK (LFSYNT) on nRF5340

RE: Unstable Distance Measurement with Synthesized LFCLK (LFSYNT) on nRF5340

_lumac — Mon, 14 Jul 2025 13:05:33 GMT

Hi Vidar,

Thanks for the explanation and the helpful links!

Just to clarify, in my current project configuration, both cores already have the same LF clock source selected.

I will proceed with trying the K32SRC_RC configuration this week and will share the results. I'm still a bit puzzled as to why the synthesized clock is causing the Distance Measurement (DM) application to crash, but hopefully, the K32SRC_RC will provide a stable solution.

Thanks again for your support!

RE: Unstable Distance Measurement with Synthesized LFCLK (LFSYNT) on nRF5340

Vidar Berg — Mon, 14 Jul 2025 12:46:43 GMT

Hello,

When selecting the clock source on the nRF5340 it is important that you make the same selection on both cores and not only on the application core. The network core FW may fail to boot if not. Configurations added to the prj.conf file in your project folder will only be applied to the main application.

You can set the default LF clock source in your board file if you are going to define your own custom board like how this boards selects the RCOSC as the default clock source for the app and network core: https://github.com/nrfconnect/sdk-zephyr/blob/81a2b95a7e78217ec0ec0173a0dc9bcc4447ea5e/boards/panasonic/pan1783/pan1783a_evb_nrf5340_cpunet_defconfig#L13 and https://github.com/nrfconnect/sdk-zephyr/blob/81a2b95a7e78217ec0ec0173a0dc9bcc4447ea5e/boards/panasonic/pan1783/pan1783a_pa_evb_nrf5340_cpuapp_defconfig#L20

Best regards,

Vidar

RE: Unstable Distance Measurement with Synthesized LFCLK (LFSYNT) on nRF5340

_lumac — Mon, 14 Jul 2025 10:44:24 GMT

Hi Turbo J,

I appreciate the information about LFSYNTH not being compatible with BTLE. I'm actively looking for documentation on that to understand the limitations better.

I'll try using the calibrated LFRC this week and will post my results back here.

Thanks for your help!

RE: Unstable Distance Measurement with Synthesized LFCLK (LFSYNT) on nRF5340

Turbo J — Fri, 11 Jul 2025 18:46:12 GMT

LFSYNTH is not compatible with BTLE operation at all, no idea where that is documented though.At least it used to be this way with NRF52x chips.

Have you tried using the calibrated LFRC? That one can be used in BTLE mode.