Verify Backdoor Key access, and Protection Override, what are these diffrences ??

[admin]

To secure and protection purpose, firmware use the appropriate flash commands.

I hope to understand the flash commands about secure / protection of S12Z processor.

"Verify backdoor access key", and "Protect override"

what are these differences ??

does anyone know the appropriate advice of answers my questions ??

Regards.    

[kef2]

S12Z processor doesn't have any flash memory. There are MCUs with S12Z CPU and flash. Since you didn't provide URL to docs or at least the name of MCU, it is hard to answer precisely. Security in these MCUs means access restrictions to read code and other IP from MCU memories. You may engage chip security to disable access to onchip memory via BDM pin. Protection usually refers to write protection. When write protection is engaged, you can't erase and write flash memory in write protected area. Verify Backdoor Key means disengaging chip security for debug or similar purposes. Protection override, hm, I really miss context from documentation, probably means changing write protection settings to write prote more flash memore than was protected before. But I may be wrong here.

[RadekS]

Thank you Edward, it is exactly how you described.

Security feature protect MCU content against unauthorized access. Unsecure is possible by three ways:

    1. Backdoor key access(temporary)

    2. Reprogramming the security bits

    3. Complete memory erase (special modes)

Ad1) For secure and backdoor key you set 16bytes on address 0xFF_FE00. Backdoor Comparison Key is at address 0xFF_FE00-0xFF_FE07. The backdoor key access method allows debugging of a secured microcontroller without having to erase the Flash. This is particularly useful for failure analysis.

For unsecure by backdoor key you use special flash command 0C (section Verify Backdoor Access Key Command in reference manual). No word of the backdoor key is allowed to have the value 0x0000 or 0xFFFF. Unsecure is valid only till reset. If an invalid attempt is made to verify the Backdoor Keys the command will be locked out until a power down occurs.

Ad2) In normal single chip mode (NS), security can also be disabled by erasing and reprogramming the security bits within Flash options/security byte to the unsecured value. Because the erase operation will erase the entire sector from 0xFF_FE00–0xFF_FFFF, the backdoor key and the interrupt vectors will also be erased; this method is not recommended for normal single chip mode.

Ad3) Complete mass erase by BDM device(in special mode). In Code Warior 10.X debugger it is handled automatically by PEmicro driver.

Protection feature protects (part of) Flash/EEPROM against accidental program or erase (for example by error in code). Typically it is used for protection of bootloader area or for protection of factory settings in EEPROM.

Protection override is new Flash module feature used in S12ZVM. The Protection Override command allows the user to temporarily override the protection limits, either decreasing, increasing or disabling protection limits, on P-Flash and/or EEPROM, if the comparison key provided as a parameter loaded on FCCOB matches the value of the key previously programmed on the Flash Configuration Field = address 0xFF_FE08-0xFF_FE09. So, Protection override is almost the same as backdoor key, but for protection = it allows temporary change/disable Flash/EEPROM protection.