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How to initialize MCG and USB without a crystal?

Question asked by László Monda on Sep 19, 2016
Latest reply on Sep 21, 2016 by Iva Dorazinova

Hi guys,

 

I'm the lead developer of the Ultimate Hacking Keyboard which is a split, Open Source keyboard.

 

So far, I successfully ported our firmware from AVRs to FRDM boards, and now I'd like to make it work on our custom PCBs.

 

Given that the IRC48MCLK is on board and capable of driving USB, I'd rather not use a crystal.

 

Apparently, the firmware of the right keyboard half which works on FRDM-K22F board doesn't work on the custom PCB of the right keyboard half, presumably because no crystal is featured on the board.

 

Execution halts when CLOCK_BootToPeeMode() gets called. Please consider the relevant line on GitHub.

 

I started to delve into the MCG and relevant topics, but it's rather overwhelming, and I have limited time to make it work, so I'm reaching out for help.

 

What should I tweak to configure the MCG and USB to work without a crystal in RUN mode and use the IRC48MCLK?

 

Any help is appreciated, and I'd be glad to pay to make this work, especially for a pull request.

 

Cheers!

- Laci

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