topic Re: security and emulation writes to flash in 8-bit Microcontrollers

security and emulation writes to flash

jah — Tue, 07 Nov 2006 01:02:40 GMT

reference the mc9s08rd32dwe processor

while using a commerical programmer production has security locked the processor by setting the flash register NVOPT/SEC01EC00 = 1:0 later at power up NVOPT gets copied to FOPT and the processor is locked. for a situation that emulation will need to write to a random flash page the processor is now locked and the write will not happen.

i need to use the backdoor, i dont know which page emulation will write to and assume all pages will be protected.

can you guys verify my fix would entail:
-i need to add code to use the NVBACKKEY register(s) the security backdoor.
-i know i need to write to NVBACKKEY[0] through NVBACKKEY[7] in order from emulation but DO I NEED TO DO THIS FROM RAM NOT FLASH!!
-can i do the writes using Clanguage like the code:
NVBACKKEY[0] = Secret[0];
NVBACKKEY[1] = Secret[1];
NVBACKKEY[2] = Secret[2];
NVBACKKEY[3] = Secret[3];
NVBACKKEY[4] = Secret[4];
NVBACKKEY[5] = Secret[5];
NVBACKKEY[6] = Secret[6];
NVBACKKEY[7] = Secret[7];
-is there ram based assy code already existing that i could use??

Re: security and emulation writes to flash

jah — Sat, 11 Nov 2006 07:45:00 GMT

bump

Re: security and emulation writes to flash

peg — Sun, 12 Nov 2006 11:14:10 GMT

Hi jah,

Here is a small test programme in all assembly that I wrote to test the backdoor function.

It was written to run on a M68DEMO908GB60 board.

You load the programme then secure the FLASH.

Then cycle power and try to get back in via BDM, you can't.

Then press SW1 and now you can but your reset vector is blank.

This is because it is just a simple test programme.

Hope this helps

David

Message Edited by peg on 2006-11-1309:01 PM