lec11a - Lecture 11alt Advances in Combinational ATPG...

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Copyright 2001, Agrawa VLSI Test: Lecture 11alt 1 Lecture 11alt Advances in Combinational ATPG Algorithms Branch and Bound Search FAN – Multiple Backtrace, head lines (1983) TOPS – Dominators (1987) SOCRATES – Learning (1988) EST – Search space learning (1991) ATPG Performance improvements Summary
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Copyright 2001, Agrawa VLSI Test: Lecture 11alt 2 ATPG: A Boolean Satisfiability Problem CUT CUT with fault f(a,b,c) = 1 Test Vector (a,b,c)
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Copyright 2001, Agrawa VLSI Test: Lecture 11alt 3 SAT is NP-Complete a c c b b 1 1 1 0 0 0 0 0 c c 0 1 f a b c f Binary Decision Diagram (BDD)
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Copyright 2001, Agrawa VLSI Test: Lecture 11alt 4 Search for a Solution Problem: Given a value of a Boolean function of binary variables, find values of the variables. Solution: Starting at the root, enumerative traversal of the binary decision diagram (BDD) until a solution is found. BDD is a search tree – search consists of Branch : Set an untried value for a variable Backtrack to previous branching point if there is no untried value Stop if solution found, or backtracked to root without untried values Or, bound search tree for future traversals if solution is impossible and backtrack to previous branching point (some variable orderings may lead to early bounding) Or, continue
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Copyright 2001, Agrawa VLSI Test: Lecture 11alt 5 Example: f = 1 a c c b b 1 1 1 0 0 0 0 0 c c 0 1 f a b c f Binary Decision Diagram (BDD) bound
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lec11a - Lecture 11alt Advances in Combinational ATPG...

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