STM32 - Erasing the flash using OpenOCD

2020/08/19

Let’s say you have flashed your STM32 MCU but accidentally overwrote a GPIO configuration used for ST-Link communication (discovery boards are prone to this). You might get the error message when trying to flash:

Error: init mode failed (unable to connect to the target)

There is a handy tool with the straightforward name STM32 ST-LINK utility which can be used to perform a full chip erase. Unfortunately this tool only works in Windows :(.

So what we unix users are “stuck with” is OpenOCD (which is awesome!). To wipe the flash we have to first put the device into reset mode. We can do this by pulling the NRST pin (see your chip’s reference manual) low. The blog post I linked to above has some more information on this.

Users of discovery boards can just press and hold the reset button. Then you can issue the following command:

openocd -f interface/stlink-v2.cfg -f target/stm32f3x.cfg -c "init" -c "halt" -c "wait_halt" -c "stm32f1x mass_erase 0" -c "sleep 200" -c "reset run" -c "shutdown"

You need to replace target/stm32f3x.cfg with the appropriate config file for your MCU. You can also try to use the configuration file for the discovery board that you’re using:

openocd -f board/stm32f3discovery.cfg -c "init" -c "halt" -c "wait_halt" -c "stm32f1x mass_erase 0" -c "sleep 200" -c "reset run" -c "shutdown"

This should have “unbricked” your device.

During the process you might get the error:

Error: timed out while waiting for target halted

I found that this is a bit of a timing issue. I found the following process to be working for me on the STM32F3DISCOVERY:

  1. Hold the reset button, then plug in the USB connector to power on the device
  2. Wait for about 1-2 seconds
  3. Release the reset button, then immediately issue the command above

Good luck!