Actively toggling HFXO when using Soft Device

[Brian Shankland]

Hello,

I need to use the more accurate HFXO for a very short interval to time incoming interrupts (approx 1/50 second every 15 mins)

The processor sleeps idle for the vast majority of the time that the Soft Device is not active on BLE. 

As the HXO is not currently selected I am assuming from related searches and replies on this site that the Soft Device turns this on when it needs it and then off again once its finished with the radio.

Ideally I would like to do the same for my short requirement of the HFXO, but I may clash with the soft device and turn it off just as BLE activity was going to be performed.

Is there a call to the Soft device to inform it that the app needs HFXO and tone to tell it when it does not in which the soft device can perform arbitration and ensure HFXO is set when either it or the app needs it and prevent either from turning it off when the other is using it?

Thanks

Brian Shankland

[Vidar Berg]

Hello,

Yes, the Softdevice include APIs to both request and release request for the HFXO. The Softdevice won't turn off the crystal as long it's being requested by the application.

Relevant Softdevice functions:

 - sd_clock_hfclk_request

 - sd_clock_hfclk_release

 - sd_clock_hfclk_is_running

Best regards,

Vidar

[Brian Shankland]

Thanks for confirmation Vidar.

Documentation for release says that the HFXO is stopped immediately, but I'm assuming that if the Soft Device is also using it that this will be delayed until it is also finished.

I will check that HFXO is running when I request it, but will not check for it stopped on release - let Soft device decide when it is safe to do so.

Thanks,

[Vidar Berg]

"immediately" is maybe not entirerly accurate. Like you said, stopping of the HFXO has to be delayed if the application releases the clock request while the clock is in use by the Softdevice (Softdevice does handle this scenario).