nRF9160DK high accuracy UART baud rates

[Soupdragon]

I'm a newbie (few weeks) with nRF9160-DK and using nRF Connect SDK v1.7.1 / VS Code on a Windows 10 PC

Good afternoon,

I'm struggling with how to set up and start the external crystal oscillator on the nRF9160DK to get high accuracy UART baud rates. I've spent hours and looked at loads of samples/applications with UART in them, and have found nothing. I've looked at Clock control documentation as suggested but thats way too advanced for me. Is there an easier way for newbies to get into this stuff ? Some nRF9160 clock setting examples that I can use and learn from under VS Code perhaps ?

Or maybe the high accuracy crystal is already selected by default, and I don't need to do anything ? Which would explain why none of the examples seem to use it. But from what I've read I don't think that is the case. I think HFXO is only started by 'triggering HFCLKSTART task', but what is that and how to do it ?

Apologies if this is a bit of a basic question, but I'm quite new to Nordic and get the feeling that there's a very obvious document somewhere that I should be reading but have somehow missed.

[kingston]

Hi Soupdragon there's a lot there to learn, but once you get the general idea of Zephyr and the SDK it'll all make sense.  My general workflow for "how do I accomplish this?" is to start with a search on the SDK page for the version I am on like 

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/search.html?q=HFCLKSTART+&check_keywords=yes&area=default

This will usually lead me to whether the topic is handled in Nordic or on Zephyr natively. 

The SDK pages will lead you to decent docs on how to use, and if nothing else other keywords you can search for here on DevZone that may lead you to an answer.

I've not modified the Clocks on my 9160, but it appears you need to work with the Clock HAL(Hardware Abstraction Layer) based on the docs.

Here's a link to an example I found.

devzone.nordicsemi.com/.../nrf52840-hfxo-and-hfclkstarted-event

[Håkon Alseth]

Great answer, kingston!

You have covered howto start HFXO directly using register access, and here's an example on how to use the clock subsys in zephyr to start the HFXO:

https://github.com/nrfconnect/sdk-nrf/blob/main/samples/nrf9160/at_client/src/main.c#L20-L29

 

Kind regards,

Håkon