Hello Evgeni Kosakovski:
The Flash memory driver C90TFS comes with an example for the use of the backdoor key. The demo is called demo_secure_<device>.
But actually the use is very simple, just involves the next procedure:
-> Store the desired 8-byte key in flash at addresses 0x0400 - 0x0407. The syntax to store the key in flash depends on your IDE or toolchain but usually there is a default flash configuration definition ready to be modified.
-> Enable backdoor key with the KEYEN bits in the NVM_FSEC byte at address 0x040C. The same FSEC byte is used to secure the device with the SEC bits. Also toolchain dependent.
-> Declare a routine in code to get the 8-byte key. This depends on your requirements, for example the key can be expected after pressing a button and waiting for the key via UART from a PC console.
-> Write 0x45 (Backdoor command) to register FCCOB0 and the received 8-byte key to registers FCCOB[4] to FCCOB[B] and launch the command by clearing the bit FSTAT[CCIF].
The attached code is how the last 2 steps are implemented in the C90TFS driver.
I hope this helps.
Best Regards!
Jorge Gonzalez
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