1. Fault Diagnosis

2. The Diagnosis Problem
General: Given the symptoms, determine the likely cause(s)
Applies to many domains: Human illness, trouble-shooting of any kind
In testing: Given test results on a failing device, {<failing test, failing outputs>}, find the likely defects/faults as the causes.
Often a preprocess to failure-mode analysis (FMA), an expensive process.
SAT-Based Diagnosis

3. Model-based vs. Model-free Diagnosis?
Model Based: Assumes the error-causing defect can be modeled by one or more of the standard fault models: SAF, Bridging, Opens, ...
Model-Free: Assumes the defect can excite any number of lines in any time frame, some of whom are observed in the same or later time frames according to the test results.
Both, however, must limit the multiplicity of causes for practical reasons.
SAT-Based Diagnosis

4. Cause-effect vs. Effect-cause Analysis?
For the given test, pre-compute the effects of all possible causes, according to an assumed fault model, and build a dictionary with effects as index and causes as contents
Diagnosis reduces to simple dictionary lookup
Effect-cause
Analyze the circuit elements connected to the outputs for observed test results and determine likely causes at the inputs of the circuit elements.
Repeat the process recursively until all possible causes are determined.
SAT-Based Diagnosis

5. Motivating Example Consider test results from c17:
Test Vector
(A,B,C,D,E)
Failing Output(s)
V1: <1,1,1,0,0> Z
V2: <0,1,1,0,1> Y
We will work through the example in class.
SAT-Based Diagnosis

6. Motivating Example (Contd.)
Now consider the results of a third test vector applied to c17:
Test Vector
(A,B,C,D,E)
Failing Output(s)
V1: <1,1,1,0,0> Z
V2: <0,1,1,0,1> Y
V3: <1,0,1,1,1>
SAT-Based Diagnosis

7. Fault Diagnosis Using Boolean Satisfiability*
* A. Smith, A. Veneris, M. F. Ali, and A. Viglas, “Fault Diagnosis and Logic Debugging Using Boolean Satisfiability,” IEEE TCAD, 24(10), Oct 2005,

8. Modeling Candidate Fault Location
SAT-Based Diagnosis

9. Counter for Multiple Faults
SAT-Based Diagnosis

10. Complete Construction
SAT-Based Diagnosis

11. Example Sequential Circuit and its ILA Representation
SAT-Based Diagnosis

12. Diagnosis in Two Cycles
SAT-Based Diagnosis

13. Sequential SAT Based Diagnosis-1
L: All lines
G: Suspect Lines
SAT-Based Diagnosis

14. Sequential SAT Based Diagnosis-2

15. Two-Pass Diagnosis Using Structure Information
SAT-Based Diagnosis

16. Model-Based Diagnosis - SAFs
SAT-Based Diagnosis

17. Experimental Results - 1
SAT-Based Diagnosis

18. Experimental Results - 2
SAT-Based Diagnosis