Illegal operation TRAP cause

Eric,

The most likely cause is the PC accessing an illegal opcode.  Possibly there is a stack overflow or the PC is running into illegal memory for come reason.

The CPU user's guide says: "As part of its operation, the illegal-instruction trap saves the return address on the stack. Thus, you can detect the offending address by examining this saved value."  Look at the SP register after the TRAP occurs to check it's in range, and if so what return value it points to.

Check also that your code doesn't put a branch just before an illegal memory range - see the "Pre-fetching beyond valid memory" advisory in the errata sheet.

Regards,

Richard