Hi

We are currently using an STM32F756IG on a custom board, which we program and configure using SEGGER JLink (SWD mode). We have been using this setup without issues for the last year or two but are now seeing occasional BRICKS caused by the automatic UNSECURE/MASS-ERASE process.

Occasionally the JLInk software will decide to do an unsecure operation (possibly due to timing/signalling issues incorrectly triggering the unsecure attempt) and after this we cannot connect to our STM32. On debug we found that the FLASH OPTION bytes were set to configure BOR_LEVEL as ON (not OFF which the datasheet suggests is default) and as a result our STM32 powered at 1V8 is being held in reset.

Currently we are struggling to reset these OPTION BYTES through software without forcing a higher voltage onto our board (dangerous for surrounding peripherals). Is there anything SEGGER suggests we can try to rectify? I would also be interested to see what the "default" values are for JLink STM32 Unlock in terms of BOR_LEVEL?

Thanks

Chris

Forcing a higher voltage onto our board to bring the STM out of reset shows that something has unlocked the flash register and left it configured with: 0x00FFAA49 (instead of default of 0xC0FFAAFC)