Typically an STM32 device gets bricked when it is flashed with an algorithm that references nonexistent memory during boot up. That puts the device in a hard fault state that won’t allow a JTAG connection. An unhelpful error message is displayed — like No STM32 MCU found — is displayed.
A hard fault lock-up can happen if you flash to the wrong part or if your algorithm indexes past the end of an array or gets a bad pointer. To unbrick your device:
1. Download and run stm32cubeprogrammer.
2. Under Mode, select Under reset.
3. Unplug your device.
4. Press and hold the Reset button on the device while you:
a. Plug in your device.
b. In stem32cube programmer, click Connect.
c. Count to three, then release the Reset button.
5. In stm32cubeprogrammer, click Erasing and Programming, then select index 0 of flash and click Erase selected sectors.
