Procedure for unwedging an STM32F0-Discovery board

[anarchitech]

Bad Flash Happens

Sometimes Things Go Wrong and you find you have a dev board in a state where you can't do anything with flash, which is now mysteriously filled with Really Weird Shit. Today's procedure covers the very recent unwedging of an STM32F051-Discovery board. Don't ask us how it happened, this board showed up in this state.

You have to sidechannel via the serial bootloader

Normal jtagging via muforth/stlink is not going to work. You have to use the serial bootloader. In the example below, we're using a PL2303, but this will work with an FTDI-2232H etc. You just need something that will do serial that has TX, RX, GND and 3.3V.

1. Put female-female jumper wires on the following pins of the PL2303: RXD, TXD, GND, 3.3V

2. Jumper BOOT0 and VDD on the F051 board with a wire or one of those nifty jumper pins pirated off one of your other boards.

3. Attach the PL2303 to the F051 board as follows:

PL2303           F051
TXD      --->    PA10/RX
RXD      --->    PA9/TX
3.3V     --->    3.3V
GND      --->    GND

... and plug it into a usb port.

4. When you build muforth on Linux, it automagically decides muforth/mu/serial-target should symlink to /dev/ttyS0. This needs
   to change because it's a nervy assumption. In this case, the PL2303 will enumerate as /dev/ttyUSB0. Let's get things set up.

$ cd muforth/mu
$ rm serial-target
$ ln -s /dev/ttyUSB0 serial-target

One more "gotcha" --- not all systems have the same idea about which device belongs to which group. Archlinux, for example, decided that this /dev/ttyUSB0 belonged to group uucp, so if you're not a member, you need to add yourself to that group, logout and log back in.

$ sudo usermod -aG uucp $USER

5. Ok, we're logged back in, we're plugged in, and the board is wired per above. Let's do some triage.

./muforth -d bootloader -f target/ARM/board/stm32f0-discovery.mu4

---- loading messages scroll by ----

(( STM32 serial bootloader support )) <--- This is important
(( ST-LINK debug No supported USB devices found ))  <--- Ignore this, it's spurious noise

boot

Bootloader Version 3.1           <---
Using extended erase command.       | <---------- You want to see this after typing boot
 Ok (chatting) (hex) (flash)     <---

@flash t.erase
NOW HIT THE BLACK RESET BUTTON ON THE BOARD

boot

Bootloader Version 3.1
Using extended erase command.
 Ok (chatting) (hex) (flash)

@flash du

.... and you should see all ffffff's

Groovy. Unplug and reconnect with the board with a normal command string:

./muforth -f target/ARM/board/stm32f0-discovery.mu4

jtag

ST-LINK/V2 JTAG V15
DFU mode => Mass mode => Debug Mode
      SP             RP              IP
ffffffe0  00000000  00000000*
WARNING: Target's flash image differs from host's. Run flash-image? Ok (chatting) (hex) (flash)

flash-image

erase page   800_0000
program      800_0000 200
program      800_0200 200
erase page   800_0400
program      800_0400 1b8 (Ok) (chatting) (hex) (flash)

verify   Ok  (chatting) (hex) (flash)
PRESS THE BLACK RESET KEY ON THE BOARD

jtag

ST-LINK/V2 JTAG V15
Debug Mode
           SP             RP              IP
20001efc  00000000  00000000*   Ok (chatting) (hex) (flash)

@flash du  should show, starting from address 08000000, an address in ram (20002000) followed by a bunch of 
addresses in 08000000 land

... and that's it, you should be good to go. ;)