debugging

9 indispensable rules for finding even the most elusive hardware and software problem

UNDERSTAND THE SYSTEM

• read the manual

• read everything in depths

• know the fundamentals

• know the road map

• understand your tools

• look up the details

MAKE IT FAIL

• do it again

• start at the beginning

• stimulate the failure

• but don't stimulate the failure

• find the uncontrolled condition that makes it intermittent

• record everything and find the signature of intermittent bugs

• don't trust statistics too much

• know that "that" can happen

• never throw away a debugging tool

QUIT THINKING AND LOOK

• see the failure

• see the details

• build instrumentation in

• add instrumentation on

• don't be afraid to dive in

• watch out for heisenburg

• guess only to focus the search

DIVIDE AND CONQUER

• narrow the search with successive approximation

• get the range

• determine which side of the bug you are on

• use easy-to-spot test patterns

• start with the bad

• fix the bugs you know about

• fix the noise first

CHANGE ONE THING AT A TIME

• isolate the key factor

• grab the brass bar with both hands

• change one test at a time

• compare it with a good one

• determine what you changed since the last time it worked

KEEP AN AUDIT TRAIL

• write down what you did, in what order, and what happened as a result

• understand any detail could be the important one

• correlate events

• understand audit trails for design are also good for testing

• write it down

CHECK THE PLUG

• question your assumptions

• start at the beginning

• test the tool

GET A FRESH VIEW

• ask for fresh insights

• tap expertise

• listen to the voice of experience

• know that help is all around you

• don't be proud

• report symptoms, not theories

• realize that you don't have to be sure

IF YOU DIDN'T FIX IT, IT AIN'T FIXED

• check that it's really fixed

• check that it's really your fix that fixed it

• know that it never just goes away by itself

• fix the cause

• fix the process