RE: UART clock accuracy

Sigurd — Thu, 16 Jan 2025 20:27:59 GMT

Hi!

[quote user=""]Inaccuracy in timing of UART at baud 115200, seems like the 2X nRF chips in my setup have difficulty talking to one another as the temperature rises. The suspicion being that the internal clock (HF) varies enough in timing and that causes enough delta that makes the bits uninterpretable for the receiver. I am reading that baud 115200 requires timing within +-2%. I can see through scope captures that the duty cycle of each bit does vary more than that at high temp. So hence the suspicion.[/quote]

Correct. You need to enable HFXO, as mentioned in the UARTE chatper for nRF52840 and nRF5340,

[quote user=""]I see some examples that directly call into clock management API (at_client sample of nRF9160), but that then requires manually calling to enable the external clock, then do I have to shut it down manually also? Doesn't sound very elegant and Zephyr'y. But if this is the only way, any further guidance would be appreciated.[/quote]

As of today the application would need to request the HFXO itself. See how it's done with e.g. this function:

https://github.com/nrfconnect/sdk-nrf/blob/v2.5.0/applications/serial_lte_modem/src/main.c#L97