A Parallel Branch and Bound Algorithm for Test Generation

For circuits of VLSI complexity, test generation time can be prohibitive. Most of the time is consumed by hard-to-detect (HTD) faults which might remain undetected even after a large number of backtracks. We identify the problems inherent in a uniprocessor implementation of a test generation algorithm and propose a parallel test generation algorithm which tries to achieve a high fault coverage for HTD faults in a reasonable amount of time. A dynamic search space allocation strategy is used which ensures that the search spaces allocated to different processors are disjoint. The parallel test generation algorithm has been implemented on an Intel iPSC/2 hypercube. Results are presented using the ISCAS combinational benchmark circuits which conclusively prove that parallel processing of HTD faults does indeed result in high fault coverage which is otherwise not achievable by a uniprocessor algorithm in limited CPU time. The parallel algorithm exhibits superlinear speedups in some cases due to search anomalies.