TonyB schrieb:
We're looking into using the JTAG security fuse in our product to prevent snooping (namely to safeguard an encryption key). However, I've been unable to find much information on this in the TI docs. I thought I had read many months ago that once the security fuse is blown, it could be reset by erasing the chip. I'm left with a few questions... Is there anyway for mspgcc to program this fuse? It looks like it is JTAG adapter specific.
burning the fuse required >7V that the adapter must provide. > Further, it looks like the TI USB FET won't work. i though it should? "msp430-jtag -l TIUSB --secure" might work.
Once blown, can the chip (and fuse) be erased via JTAG or firmware?
the BSL isn't influenced by the security fuse. the fuse can't be "repaired", thus the JTAG is permanently disabled. the BSL has different features depending on chip F1xx, F4xx: mass erase is always possible. access with password too. F2xx: BSL can be disabled, or set to mass erase on first wrong password. > It looks like it can only be done with the BSL.
Can the fuse be set by firmware? Doesn't look like it...
no the JTAG circuitry is not accessible from within a program running on the chip
I'm about to send off the production board, but it looks like I'll have to add the BSL connector. I should have looked into these issues before laying out the board.
you must use JTAG if you want to blow the fuse. disabling the BSL in F2xx chips can be configured by a value at a specific address. that can be part of the normal firmware.
chris
