RE: When does the SoftDevice enable the external 32MHz crystal oscillator?

Vidar Berg — Wed, 30 Oct 2024 08:49:17 GMT

Hello,

Yes, HFINT is the default clock source and is used most of the time. Unless the application specifically requests the crystal oscillator (HFXO), the Softdevice will start and stop the crystal oscillator for each protocol event since keeping the crystal oscillator running significantly increases idle current (from 2-3uA to ~200uA).

For example, this is what a typical advertisment event look like ( Online Power Profiler for Bluetooth LE )

[quote user=""]I've tried printing the state of the oscillator using sd_clock_hfclk_is_running(). I was expecting to see the oscillator disabled while Advertising is disabled, and then enabled when Advertising is enabled, however, the function outputs "0" before and after.[/quote]

The crystal oscillator will only be enabled during the advertisment events.

[quote user=""]Is it correct to say that if advertising is disabled and there's no active connection, the external oscillator is not running?[/quote]

The HFXO is also used for periodic calibration when the LFRC oscillator is selected as the 32KHz clock source. But it will only be kept on during the calibration event.

Best regards,

Vidar