Ibrahim Demir

Flash Security Issue on CFM

Discussion created by Ibrahim Demir on Sep 25, 2008
Latest reply on Sep 26, 2008 by Rich Testardi
I have some problems understanding flash security feature of the coldfire device MCF52233. There is no obvious definition of the flash security in the reference manual. Only information about it is

"Security information that allows the MCU to prevent intrusive access to the flash memory is stored in the
flash configuration field." on page 249

What kind of intrusive accesses? Is there a list about it? After I made some trials I found out that BDM interface is disabled totally when flash security is enabled. It seams to be illogical to me. What is the relation between BDM and flash security. Is this mentioned in the reference manual? Or any other document?

One other question is what is the use of backdoor access? For which purpose can it be used? Code running from the flash have all kind of access to flash in secure mode. Why does running code need such a bypass?
To enable BDM interface? No use, BDM resets the device and it is secured aggain.

If BDM were not disabled, it may run the required sequence to bypass the security if the key was known. Then it may have a meaning.

Is there somebody effectively using the flash security bypass feature?