I am not able to build a bootloader successfuly with latest sources from
https://github.com/adafruit/uf2-samdx1
nor any older one…
I’d like to have the improvements of a newer build / release, beacuse sometimes the flash gets corrupted or the board does not start after powerup.
So please let me know, what you have changed to the bootloader code so that it works or
release a working codebase (i.e. fork the uf2-samdx1 and release it for the public)
I hope sparkfun will take this into account seriously.
Our version lives here for that processor MicroMod_Processor_Board-SAMD51/uf2-bootloader at master · sparkfun/MicroMod_Processor_Board-SAMD51 · GitHub - you can file an ‘issue’ on the github page(s)
Do you mean file an issue on the sparkfun repository?
I also found another very stange behaviour!
I have got 5 pieces MicroMod-SAMD51 boards. Three of them are populated with an ATSAM53J19A instead of ATSAMD51J20A MCU. But the Amtel-ICE detects them correctly as ATSAMD51J20A! How is this possible - are these parts wrong labled ?
The ATSAM53J19A has only 512KB Flash - but was able to successfully write/read th whole 1MB (like @ ATSAMD51J20A).
Yes
That is odd, but sometimes parts can indeed be mislabeled from their MFR…the important part is whether it is recognized as -20A and has the full 1MB, so in this case it should be good to go 
I have now opened a issue on github:
https://github.com/sparkfun/MicroMod_Processor_Board-SAMD51/issues/4