nrf54L15 clock output accuracy using GRTC Clock output

RE: nrf54L15 clock output accuracy using GRTC Clock output

Emil Lenngren — Fri, 28 Feb 2025 09:49:10 GMT

In your code you are using the "fast clock" output. This will use either the HF oscillator (which is inaccurate) in case HFXO is turned off, or HFXO in case it is turned on.

You should use LFCLK as output instead. Assuming you run GRTC from LFXO, the accuracy should follow that one, which should be +-10ppm or whatever accuracy your external LF crystal has. Note that that will give you a 32 kHz clock output and devisor is not used here.

RE: nrf54L15 clock output accuracy using GRTC Clock output

Tjaz — Fri, 28 Feb 2025 09:43:49 GMT

Ok thanks,

How do I do that? What is the API to call? (We are on NCS 2.9.0)

Doesn't the fact that the Peripheral clock is requested by the GRTC peripheral mean that the oscillator is turned on? Or does the HFCLOCK come from somewhere else?

BR,
Tjaž

RE: nrf54L15 clock output accuracy using GRTC Clock output

Simonr — Fri, 28 Feb 2025 09:29:55 GMT

We expect this only to be valid when the HFXO (external high frequency oscillator) is explicitly started by the application. It does not seem like the HFXO is actually started in your project. Please make sure that it is started and runs before you start the GRTC output on your end.

Best regards,

Simon

RE: nrf54L15 clock output accuracy using GRTC Clock output

Tjaz — Tue, 25 Feb 2025 07:27:36 GMT

Ok, but have you managed to recreate it?

RE: nrf54L15 clock output accuracy using GRTC Clock output

Simonr — Mon, 24 Feb 2025 14:03:23 GMT

Thank you for your input. I've not been able to make any progress on my end here, but I have now involved some of the developers to take a look at this as well as there might be an issue/bug somewhere. I'll get back to you when I know more (Friday at the latest). Thank you for your patience!

Best regards,

Simon

RE: nrf54L15 clock output accuracy using GRTC Clock output

Tjaz — Thu, 20 Feb 2025 07:23:13 GMT

I have tested this on a nrf54L15DK.

It is a nRF54L15-PDK v0.8.1

I also tested this on custom PCBs we have made, where we also observe this king of error - but the error is different across different PCBS, some are bellow 32khZ (31.887 kHz for example), some are above (similar to the DK).

BR,
Tjaž

RE: nrf54L15 clock output accuracy using GRTC Clock output

Simonr — Wed, 19 Feb 2025 11:46:30 GMT

Just to make sure, are you working on an nRF54L15 DK when seeing this drift? If you are working on a custom board I would double check that the HF crystal is loaded correctly, and that this isn't caused by drift on the crystal itself. Can you also let me know what version of the DK you're working on, and I'll see if I can reproduce this on my end.

Best regards,

Simon