Add board: Seeed XIAO BLE

[ssievert42]

This adds support for the Seeed XIAO BLE, a tiny development board with a nRF52840 and 2 MB of external flash.

The board definition file is based on this one by Espruino forums user parasquid.

Some goodies that are included as well:

• the build generates an UF2 image, that can be flashed to the board when it is in bootloader mode, without needing to install anything on the host (connect via USB, double press the reset button, then copy the file to the USB drive that appears)
• automagically built UF2 image with GitHub actions
• E.rebootToDFU() triggers a reboot to UF2 bootloader mode

[gfwilliams]

Thanks - this looks great!

Do you think it'd be possible to change jswrap_espruino_rebootToUF2 just to use jswrap_espruino_rebootToDFU though? There's already the stuff in there for it so all you'd have to do is rename jshRebootToUF2Bootloader to jshRebootToDFU in jshardware.c and change the "ifdef" : "STM32F4", line to "#if" : "defined(STM32F4) || defined(ESPR_HAS_BOOTLOADER_UF2)",

[ssievert42]

Thanks for the feedback!
I've now dropped E.rebootToUF2() in favor of E.rebootToDFU(), mentioned the UF2 bootloader mode in the docs of E.rebootToDFU() and changed the other stuff as you suggested - no need to have two functions with slightly different names that basically do the same thing :)

[ssievert42]

Does the board definition file need to use pinutils.generate_pins()?
I don't remember why I decided to change get_pins() to not use pinutils.generate_pins(), but I think the reason was to have pin names that are the same as the ones printed on the board.

[gfwilliams]

What happens if this is .uf2? It may be you don't need the ifdef XIAOBLE ... proj: $(PROJ_NAME).uf2 line if it is...

[gfwilliams]

This looks great, thanks! Please could you add a comment in https://github.com/espruino/Espruino/blob/master/README_BuildProcess.md#infomakefile-definitions though? I'm trying to keep all the defines documented somewhere

[gfwilliams]

It's a shame the board doesn't have a button so this is needed - but I feel like it's very unlikely anyone would make a custom build that includes this?

Maybe you could:

• Make the UF2 include the flash area used for saved code so it always overwrites it
• Make a special UF2 that just overwrites the saved code area to allow you to clear it if you want to?

[gfwilliams]

Thanks for those changes to UF2 reboot - that looks really good.

Does the board definition file need to use pinutils.generate_pins()? ... I think the reason was to have pin names that are the same as the ones printed on the board.

No, that's fine - generate_pins was just a utility function to generate a bunch of contiguous pins. If you want to renumber the pins so they match the board what you've done is the right way to handle it.