Debugging

1. Debugging Michael Bruce-Lockhart

2. Debugging • The first 3 rules of debugging are • 1. Location 2. Location 3. Location • Find where the fault is • Isolate subsystems • Isolate factors • Apply simplified test signals • Write special test code Debugging

3. Example Fully integrated Feedback +5 Lots of wires Tracking A/D Converter Block Dagram Debugging

4. What can go wrong? • Incorrect wiring • Broken connection • Loading • Bad Power • Bad Ground • Faulty chip • Incorrect design • Interface disagreement Debugging

5. Prevention • Good wiring • Robust • Well-organized • Good power and ground • Subsystems easy to isolate & test • Chips easy to replace • Design • KISS • Remember what’s critical • Well specified interfaces • Loading Debugging

6. Finding the problem • First objective is to localize the problem • Do cheap tests before expensive ones • check power with a scope • check grounds with an ohmmeter • check right at the pins • Substitution of parts • isolate before removing part • don’t damage the part in the removal • be careful not to blow out multiple parts • Anything can go wrong – even wires break Debugging

7. Develop the right attitude • Problems will occur • Perfection is not possible • Treat a fault as an engineering problem • Tackle it systematically • Use your brain – no substitute for thinking • Use your knowledge • If it’s a tough one • Walk away from it & rethink it Debugging

8. Finally • Document your problems • Log book • By the time you’re done you will know it thoroughly • You may forget the details a month later • It can break again Debugging