Hi Max, thank you for all this effort. Your links to various documents are greatly appreciated.
I was able to get the board into DFU mode by applying the boot0 jumper and pressing reset. I had to install STM32cubeProgrammer to get the driver. The hardware is vid=0483&pid=df11, so I changed your json file to
"hwids": [
[
"0x0483",
"0xDF11"
]
]
(removing the other hwids entry, because it didn’t work otherwise). I was able to upload to the board successfully. I then removed the boot0 jumper and reset the board. Unfortunately the LED isn’t blinking, and no USB device is found (so there’s no Serial output).
I’m unsure how to proceed. I can get back to DFU mode and flash the code again, but it doesn’t seem like the board is executing the code. Commenting out the PA13 LED stuff (leaving only the SerialUSB printing) doesn’t make a difference, so I don’t think PA13 is causing a conflict.