STM32F407 encryption phenomenon one case

There #define OB_RDP_LEVEL_1 ((uint8_t) 0x55) in the header file

Code also calls HAL_FLASHEx_OBProgram (& OptionsBytesStruct)

Then it becomes 0x55, the code is read protected.

 

STM32CubeProgrammer with the fuse back to AA, with ST Link V2, can be downloaded, but also debugging! Just when prompted PC running constant at 0xFFFFFFFE.

The fault-tolerant too strong, let keil can go so far. I looked a long time did not see anything wrong with projx file, yesterday always thought it was something wrong with debug menu.