Samd51 mm flash

[stonehippo]

This is a fix for #5590. The Sparkfun SAMD51 MicroMod has an external flash module that requires two pins to be pulled HIGH before the module is fully enabled.

This update adds a hook that allows for board.c to include a method external_flash_setup(), which get called before the flash filesystem is init'ed (which happens before board_init()). It also implements this method for the Sparkfun SAMD51 MicroMod so that the flash chip works and CIRCUITPY can be set up and mounted correctly.

This only works with the latest version 1.3 of this MicroMod board (the previous version 1.2 has a design flaw that prevents hardware SPI from working with the external flash chip).

[stonehippo]

I removed the compiler flag and switched to using an MP_WEAK implementation, based on a suggestion from @dhalbert. I think this is ready for a review once the checks have passed.

[stonehippo]

Hmm, check failed, but looking at it, the issue was related to getting a dependency for the fomu (there was a certificate error). Doesn't seem to have anything to do with the PR itself, just bad timing.

What's the best way to get the checks run again?

[dhalbert]

This is great! Thanks for fixing and add the new setup mechanism.

[stonehippo]

Thanks, @dhalbert. I just rebased on latest main and pushed to rerun the checks. Hopefully everything passes and this can get merged in.

[dhalbert]

One thing I realized: could you move the MP_WEAK function to supervisor/shared/external_flash/external_flash.c? And add a declaration in supervisor/shared/external_flash/external_flash.h? That makes it more like the other MP_WEAK uses.

[stonehippo]

Ah, good call! I'll do just that.

[stonehippo]

Huh, that broke the RP2040 builds. I guess I need to figure that out.

[dhalbert]

Thanks for working on this!