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Fault Diagnosis. The Diagnosis Problem. General: Given the symptoms, determine the likely cause(s) Applies to many domains: Human illness, trouble-shooting of any kind
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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
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
Cause-effect vs. Effect-cause Analysis? • Cause-effect: • 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
Motivating Example • Consider test results from c17: We will work through the example in class. SAT-Based Diagnosis
Motivating Example (Contd.) • Now consider the results of a third test vector applied to c17: SAT-Based Diagnosis
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, 1606-1621.
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Sequential SAT Based Diagnosis-1 SAT-Based Diagnosis
Sequential SAT Based Diagnosis-2 SAT-Based Diagnosis
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Model-Based Diagnosis - SAFs SAT-Based Diagnosis
Experimental Results - 1 SAT-Based Diagnosis
Experimental Results - 2 SAT-Based Diagnosis