softdevice and low frequency clock source

[energy]

Hello,

I've noticed the following sentence in s132_nrf52_3.x.x release notes:

"Synthesized low frequency clock source is not tested or intended for use with the BLE stack."

Could you clarify, does this means that correct low frequency clock settings are:

• NRF_CLOCK_LF_SRC_RC
• NRF_CLOCK_LF_SRC_XTAL

And that NRF_CLOCK_LF_SRC_SYNTH should not be used ?

Thanks

[Collin]

Possibly helpful info from my memory and quick searches:

• calling sd_app_evt_wait shuts down the CPU and HFCLK.
• calling sd_app_evt_wait does NOT shut down LFCLK by default, unless you set NRF_CLOCK->TASKS_LFCLKSTOP = 1; see here LFCLK is used by timers to wake the firmware, which is why the SoftDevice doesn't power them off by default. IIRC, the SoftDevice may also need an LFCLK to function properly, and use it behind the scenes. They may be warning about using the synthesized LFCLK with the SoftDevice because a lot of what the softDevice does is driven by interrupts that may come from an LFCLK timer, and if you synthesize LFCLK, then you'll lose it when HFCLK goes down...