Hacking the Xbox

APPENDIX E
Debugging:
Hints and Tips
Don’t Panic!
Developing your debugging skills is as important, if not more important,
than developing your design skills. The most important single piece of
advice is to never panic: randomly tweaking and changing things will
introduce more uncertainty and bugs than it will fix.
Debugging is simple when given total visibility into a system and total
knowledge of the expected state of a properly working system. Simply
comparing the observed state against the expected state will elucidate what
went wrong. Unfortunately, the world rarely works this way. Chips are black
boxes, and the only visibility into the internal state of the chip is through its
pins. Many signals are also too difficult to directly measure or record. Also,
the specifications provided by manufacturers are often vague or difficult to
interpret. Thus, the real art of debugging is in tracing a set of symptoms to
a root cause despite a lack of visibility and total system knowledge.
Understand the System
Trying to debug a system without first understanding what you are trying to
debug is like trying to read a Japanese comic without any knowledge of
Japanese. You can figure out at a superficial level who is the bad guy and
who is the good guy, but you get really lost as to exactly what the floating cat
has to do with all of it. In order to fully understand the plot, you need a
Japanese dictionary and a lot of time and patience. Similarly, basic electronics
principles and intuition will get you to the point where you know roughly