https://github.com/BLavery/STM32F407VG-Micropython
some notes on setting a generic 100-pin STM32F407VG running on MicroPython.
I say "generic", but what I used was the "DIY" or "DIY-MORE" $10 board from China.
It simply breaks out every GPIO, and the only on-board "extras" are LED on PE0, and USER BUTTON on PD15.

Included there is a firmware DFU image that matches this board.