In BF50XF datasheet, it is said as:
• 128-bit user programmable OTP cells
• 64-bit unique device number
Need to check with if this device number is unique per CHIP, which means that each chip will has an exclusive device number.
I thought maybe this unique device number could generate the OTP number by some algorithm designed by user, and the code could check the OTP run-timely. Or you may have some better method to increase the security of code in on-chip FLASH in BF50XF.