Adding Daisy Seed stm32H750 board - initial support

[snkYmkrct]

What works so far:
CircuitPython code is running fully from the QSPI flash
A special bootloader is needed to start execution.
Board shows up as USB drive, and there is a small file system on the internal flash - can edit code.py
Can blink the on board LED and use the BOOT button in user space

Workflow:
The CircuitPython binary is flashed with the STM32CubeProgrammer on the external flash at address 0x90000000, using the custom made external loader for the IS25LP064A QSPI flash, found here
On the internal flash, at address 0x08000000, there is a custom bootloader (download here) that does the chip and QSPI initializations, and sets the external flash in memory mapped mode for code execution.

The source code for the bootloader and the external loader are in the main and external-loader-for-cube-programmer branches of this repo https://github.com/snkYmkrct/Snakey-Boot-for-Daisy

WIP:
Add the rest of the board pins in the definition file.
Add SDRAM support
Figure out if the external flash can be used by swapping between memory mapped mode and writeable mode, so the file system can be expanded.

[dhalbert]

Thanks!

Is there a hope that your custom bootloader might be taken back by Electrosmith, or you might collaborate with them about this? Do they have something similar?

[snkYmkrct]

Thank you for the review!
I will make the required changes -- it seems I'm left with some old style files from when I started work on this.

I am not collaborating with Electrosmith, I just tackled this project as a personal challenge, after seeing a lot of people ask for CircuitPython / micropython support for the Daisy Seed board.

Electrosmith do have their own bootloader, but it is still closed source, and they seem very reluctant to share the code or any details about it. I am not sure if it could be used instead of my bootloader, since I did not test it.

My bootloader is simple, it just does minimal chip startup, initializes the QSPI flash, and jumps to running the code from there.
I created it from scratch, both for better understanding of how everything works, and to have a configuration file for the IS25LP064 flash chip ready to integrate into CircuitPython, if necessary.

Ideally, I would like to add support for the UF2 bootloader in future updates.