RE: Access to the 32 kHz clock on nRF54L15

Tom Weber — Mon, 15 Sep 2025 10:59:07 GMT

Thank you, I will look into this.

RE: Access to the 32 kHz clock on nRF54L15

Emil Lenngren — Fri, 12 Sep 2025 17:39:23 GMT

You can use the GRTC for this as it is always synchronised to the low frequency clock, regardless if it is "active" or not. Even though it uses the 16 MHz clock when it is active, it calibrates itself towards the low frequency clock at every low frequency clock tick (or often enough at least). That said, every 1 µs GRTC "tick" can typically last 14-18 ticks of the 16 MHz clock. The extreme conditions happen when you run the HF clock from HFINT in extreme temperatures and the MPSL isn't running (when MPSL is running it synchronises the HFINT against HFXO every 4th second).

Note that the GRTC uses the LF clock whenever it is not active, regardless if the 16 MHz clock is running or not. The conditions for being in the active state are listed in the GRTC documentation. Typically it gets briefly set to active if you touch its registers, or when a scheduled COMPARE event is about to be triggered soon.

My suggestion is that you use DPPI to connect a COMPARE event of GRTC to trigger a CAPTURE task of a TIMER some time in the future. Then connect another such trigger exactly 1 second later in the future (according to GRTC's time base). Then take the difference between the TIMER's two CC values. It is probably only meaningful to do this while the HFXO is running.

RE: Access to the 32 kHz clock on nRF54L15

Tom Weber — Tue, 09 Sep 2025 13:41:31 GMT

Thank you!

RE: Access to the 32 kHz clock on nRF54L15

Einar Thorsrud — Tue, 09 Sep 2025 13:14:58 GMT

Hi Tom,

This is a special use case, but I do understand your point and the desier to avoid having to putput the clock on a GPIO when this could in principle be done internally in the SoC (as is the case on the nRF52 and nRF53). I am looking into this and will get back to you.