You utilize some tool or method to run the CRC algorithm on the program ROM image after the code is assembled / compiled and linked. This "correct" code is then placed in to the ROM image as part of the program. Now at run tine at each power up you have the processor run the same method to compute the CRC of the program mwmory space. It must be exactly the same process of course. This calculation leads to some computed CRC which should compare to the one stored in the ROM image. Just have the processor perform an equality check to determine pass fail.

Michael Karas