RE: Using external low swing clock source with softdevice

Steve — Tue, 12 May 2020 14:33:42 GMT

This worked, thank you. We did however, have some issues because it wasn't clear in sdk_config that we needed to set the following when setting source as Xtal

NRF_SDH_CLOCK_LF_RC_TEMP_CTIV 0

NRF_SDH_CLOCK_LF_RC_CTIV 0

Otherwise softdevice returns an error.

RE: Using external low swing clock source with softdevice

Håkon Alseth — Tue, 12 May 2020 11:26:49 GMT

Hi,

[quote user=""]sdk_config.h lists external low swing external source options for the clock driver, but NRF_SDH_CLOCK_LF_SRC has no such option. When trying to use the 131073 value listed for NRFX_CLOCK_CONFIG_LF_SRC, the compiler throws an error, apparently softdevice can only accept an 8 bit value, even though the LFCLKSRC register documents setting bit 17 for external sources instead of Xtals. [/quote]

Yes, this is an unfortunate option that is lacking when initializing the softdevice. The workaround is to set NRF_SDH_CLOCK_LF_SRC to xtal, and manually start the xtal prior to initializing the softdevice.

[quote user=""]What's the right way to use an external source with softdevice? We're on version 16 of the SDK with S140, nRF52840.[/quote]

You can follow the configuration as posted by my colleague here: https://devzone.nordicsemi.com/f/nordic-q-a/60702/enable-bypass-of-lfclk-crystal-oscillator-with-external-clock-source

You should configure the low swing according to this table: https://infocenter.nordicsemi.com/topic/ps_nrf52840/clock.html?cp=4_0_0_4_3_1#concept_xkj_np1_2r

Please let me know if you run into any issues.

Kind regards,

Håkon