Or, if you need more flexibility, some kind of out-of bound mechanism that doesn't rely on the OS that is booting and you are trying to verify. This could be lo

Or, if you need more flexibility, some kind of out-of bound mechanism that doesn't rely on the OS that is booting and you are trying to verify. This could be loaded via some kind of internal memory card or via an interface that requires access to the board. This opens you up to physical attacks but you get a bit of a middle ground between security and flexibility.