Debugging Overview

DEBUGGING RULES

UNDERSTAND THE SYSTEM
MAKE IT FAIL
QUIT THINKING AND LOOK
DIVIDE AND CONQUER
CHANGE ONE THING AT A TIME
KEEP AN AUDIT TRAIL
CHECK THE P LUG
GET A FRESH VIEW
IF YOU DIDN'T FIX IT, IT AIN'T FIXED

This is the first rule because it's the most important. Understand?

• Read the manual. It'll tell you to lubricate the trimmer head on your weed whacker so that the lines don't fuse together.
• Read everything in depth. The section about the interrupt getting to your microcomputer is buried on page 37.
• Know the fundamentals. Chain saws are supposed to be loud.
• Know the road map. Engine speed can be different from tire speed, and the difference is in the transmission.
• Understand your tools. Know which end of the thermometer is which, and how to use the fancy features on your Glitch−O−Matic logic analyzer.
• Look up the details. Even Einstein looked up the details. Kneejerk, on the other hand, trusted his memory.

Better yet, don't remember "Keep an Audit Trail." Write down "Keep an Audit Trail."

• Write down what you did, in what order, and what happened as a result. When did you last drink coffee? When did the headache start?
• Understand that any detail could be the important one. It had to be a plaid shirt to crash the video chip.
• Correlate events. "It made a noise for four seconds starting at 21:04:53" is better than "It made a noise."
• Understand that audit trails for design are also good for testing. Software configuration control tools can tell you which revision introduced the bug.
• Write it down! No matter how horrible the moment, make a memorandum of it.