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STM32F407 RDP issue and flash corruption

Question asked by tr on Nov 21, 2014
Latest reply on Nov 21, 2014 by tr

I'm experiencing strange issues with a product based on STM32F407. When doing short power outages to the PCB (uses 24VAC), it sometimes erases or corrupts flash page(s) that are used for eeprom emulation. Pages are 1 and 2 from address 0x08004000. When I try to read flash with ST-link I notice that readout protection has been set to level 1 for some reason, so it's impossible to see what has happened to flash. In my application code I never call FLASH_OB_RDPConfig, so it can't go to level 1 from the application. Also the first line after systemInit() in Main locks the flash memory so I can't figure out what causes the erase.
The power outage has been tested with longer power outages (couple of seconds) automatically multiple thousand times without the problem. Could anyone have a clue what causes this behaviour with short power outages?