Guide: When an STM32 F3 boot loader seems bricked

[GAntonjo]

I have one 10 DOF Mini F3 FC from Banggood that I will use on my V3, upgrading it from the old APM 2.6 clone I have used so far. I could have used an F3FC board from David. One reason for not chosing the F3FC is that it does not support soft serial (currently) and as such I have limited possibilities when it comes to extra gadgets. Another is that the F3FC already is installed in my MiniTri;-)

Well, before tearing apart my V3, I first flashed TriFlight 0.5 Beta, just to test that it would run on the Mini F3 board. All OK, no problems flashing the board. Since I want to have better GPS functionality, I decided to install the INav FW on the board, and so I did. No problems with that either. However, since INav still is not updated with latest improvements from TriFlight, I have decided to revert to TriFlight again. Here problems showed up. The Mini F3 did not show up in DFU mode when shorting the Boot pads. Looking in the Device manager of my Windows 7 (and Windows 10) PC, I could see the USB port being recognized, but not as DFU. It was installed as a CP2104 USB Serial device. Trying to flash to this port from CleanFlight configurator (CFC) failed as CFC did not manage to connect to that port. I reinstalled the VCP with Serial Enumeration driver but still no luck (double checked that I tried correct COM port).

So, more googling around on how to program STM32 over CP2104 USB port, I found STMicro’s STM32 Flash loader demonstrator and downloaded that free tool. Now, this tool managed to talk to the Mini F3 board and through this tool I managed to flash TriFlight 0.5 to the board (with Global Erase enabled).

Bottom line is, if the board lights up when connected to the USB, there are hopes even if CleanFlight Configurator does not manage to flash the board;-)

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