A functional fault model for sequential machines

Abstract
This paper proposes a fault model in the state transition level for finite state machines. In this single-state-transition (SST) fault model, a fault causes the destination state of a state transition to be faulty. The effectiveness of this model is shown by both analysis and experimental results. The analysis shows that a test set that detects all SST faults will also detect most multiple-state-transition (MST) faults in practical finite state machines. Because any defective sequential machine may be viewed as having a multiple-state-transition fault of some arbitrary multiplicity, the high coverage of multiple-state-transition faults implies that the quality of the test set generated for SST faults is close to that of the sequences derived from the checking experiment. It is also shown that the upper bound of the length of the SST fault test is 2 . M - N2 for an N-state M-transition machine, while that of the checking sequence is exponential. Based on the fault model, the authors developed an automatic test generation algorithm and built a test generation system named FTG. Experimental results show that the test set generated for SST faults achieves high single stuck-at fault coverage as well as high transistor fault coverage for a multilevel implementation of the machine. The achieved transistor fault coverage is considerably higher than that of the test set generated for single stuck-at faults.

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