Lesson learned :(

[OutoftheBOTS_]

It seems if you want to flash firmware to a STM32F4 via a DFU file using Dfuse no matter how many times you try to put the MCU in boot loader mode by connecting boot0 to GND and even if you open a brand new dev board it never works. only after several hours trying everything you can think of will you discover that to put the STMF4 into boot loader mode you have to in fact connect boot0 to 3.3v

[tve]

Yeah... I don't know how many times I've cursed the ESP boot & flashing stuff, specially in the esp8266 days. Until I had to deal with the STM32 booting/flashing mess...

[pythoncoder]

Not the only pitfall. You can (temporarily) cattle a Pyboard by flashing the wrong firmware. I almost always build my own so I use a script which detects the type of board, builds the correct firmware, puts the board into DFU mode and flashes it. Completely idiot (me) proof and saves fiddling around with jumpers. I have variants of the script for projects with special requirements.

See [ull=https://github.com/peterhinch/micropyth ... /fastbuild[/url].