1) Wonder what would happen if I did that?
2)If it didn't work, could I get my Phatbox working correctly again?
as far as I know, the firmware that you could flash is the same as the retail version. There is another section of firmware that you can't update... but I don't know how to verify that
The question is: what's the purpose of the firmware that can be updated?
- Surely headunit communication
- Highly likely booting the kernel on ignition
- What else?
The second point would imply that it validates the kernel image using its signature. Doing so would also require the public key to be stored within that firmware code - but even that doesn't take us any further :-/
Para