On-Line Pruning of ZBDD for Path Delay Fault Coverage Calculation

Fatih KOCAN  Mehmet H. GUNES  Atakan KURT  

IEICE TRANSACTIONS on Information and Systems   Vol.E88-D   No.7   pp.1381-1388
Publication Date: 2005/07/01
Online ISSN: 
DOI: 10.1093/ietisy/e88-d.7.1381
Print ISSN: 0916-8532
Type of Manuscript: Special Section PAPER (Special Section on Recent Advances in Circuits and Systems--Part 1)
Category: Programmable Logic, VLSI, CAD and Layout
path delay fault,  simulation,  on-line pruning,  ZBDD,  

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Zero-suppressed BDDs (ZBDDs) have been used in the nonenumerative path delay fault (PDF) grading of VLSI circuits. One basic and one cut-based grading algorithm are proposed to grade circuits with polynomial and exponential number of PDFs, respectively. In this article, we present a new ZBDD-based basic PDF grading algorithm to enable grading of some circuits with exponential number of PDFs without using the cut-based algorithm. The algorithm overcomes the memory overflow problems by dynamically pruning the ZBDD at run-time. This new algorithm may give exact or pessimistic coverage depending on the statuses of the pruned nodes. Furthermore, we re-assess the performance of the static variable ordering heuristics in ZBDDs for PDF coverage calculation. The proposed algorithm combined with the efficient static variable ordering heuristics can avoid ZBDD size explosion in many circuits. Experimental results for ISCAS85 benchmarks show that the proposed algorithm efficiently grades circuits.