FIRE is a novel Fault-Independent algorithm for combinational REdundancy identification. The algorithm is based on a simple concept that a fault which requires a conflict as a necessary condition for its detection is undetectable and hence redundant. FIRE does not use the backtracking-based exhaustive search performed by fault-oriented automatic test generation algorithms, and identifies redundant faults without any search. Our results on benchmark and real circuits indicate that we find a large number of redundancies, much faster than a test-generation-based approach for redundancy identification. However, FIRE is not guaranteed to identify all redundancies in a circuit. ______________ Index terms: Redundancy identification, automatic test generation, logic synthesis 1. Introduction An automatic test generation (ATG) algorithm spends a large portion of its time dealing with undetectable faults. A fault is undetectable if there exists no test to detect it. A fault is identified as ...

We analyze all signals of a combinational circuit simultaneously for redundancy. The state of a signal is represented by two binary variables. The first variable is the logic value of the signal. The second variable is the observability status of the signal with respect to all primary outputs. Boolean equations specify local relationships of these variables in a manner similar to the neural network or Boolean satisfiability method. All pairwise terms appearing in these Boolean equations are used to construct an implication graph, for which the transitive closure graph is obtained. Any signal assignments or relations found from the transitive closure are substituted into higher-order terms of the Boolean equations, some of which reduce to pairwise terms. Such cases are iteratively included in the transitive closure until no more reductions are possible. In the final transitive closure, all signals are examined for the following conditions of redundancy: (1) If a signal and its complement imply each other (contradiction) then both stuck-at faults on that signal are redundant; (2) If one value implies the other value (fixation) then one of the stuck-at faults on that signal is redundant; (3) If the true observability status of a signal implies its own false observability status, then both stuck-at faults of that signal are redundant; (4) If a certain value of a signal implies the false observability status, then the corresponding stuck-at fault is redundant. Despite the apparent similarities with the transitive closure based ATPG, the present method is quite different. Here transitive closure is computed just once, and not recomputed or updated separately for each fault as required in ATPG. We give ISCAS '85 benchmark results. For c6288, we could identify 31 out of 33 redu...

We present a fault-independent redundancy identification algorithm. The controllabilities and observabilities are defined as Boolean variables and represented on an implication graph. A major enhancement over previously published results is that we include all direct and partial implications, as well as node fixation. The transitive closure, whose computation now requires a new algorithm, provides many redundant faults in a single-pass analysis. Because of these improvements, we obtain better performance than all previous faultindependent methods at execution speeds that are much faster than any exhaustive ATPG. For example, in the s9234 circuit more than half of the redundant faults are found in just 14 seconds on a Sparc 5. All 34 redundant faults of c6288 are found in one pass. Besides, our single pass procedure can classify faults according to the causes of their redundancy. The weakness of our method, as we illustrate by examples, lies in the lack of a formulation for the observabilities of fanout stems.

Redundant logic in a digital circuit is often identified as untestable or redundant single stuck-at faults. Redundant faults in a combinational circuit are faults that no input patterns can detect [2]. Removal of such faults simplifies the circuit without chang\Lambda Student