This is something I'm curious about...
Since the AVR architecture does not have privilege levels and CPU exceptions, what happens if you try to perform some kind of illegal operation (access a nonexistent physical memory address, execute an illegal instruction, etc)? Does the chip reset, crash, or just continue on its way?
Does the AVR even have illegal instructions? I looked at an opcode list and it seemed from a quick glance that nearly all bit combinations are used, and some opcodes are even duplicated...