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Unformatted text preview: Test Generation 183 Algorithm 7 PODEM C f 1: 2: 3: 4: 5: 6: 7: 8: initialize all gates to don'tcares; Dfrontier = ; result = PODEMRecursion C ; if result == success then print out values at the primary inputs; else print fault f is untestable; end if Algorithm 8 PODEMRecursion C 1: 2: 3: 4: 5: 6: 7: 8: 9: 10: 11: 12: 13: 14: 15: 16: 17: 18: 19: if faulteffect is observed at a PO then return (success); end if g v = getObjective C ; pi u = backtrace g v ; logicSimulate_and_imply pi u ; result = PODEMRecursion C ; if result == success then return(success); end if /* backtrack */ logicSimulate_and_imply pi u ; result = PODEMRecursion C ; if result == success then return(success); end if /* bad decision made at an earlier step, reset pi */ logicSimulate_and_imply pi x ; return(failure); According to the algorithm in PODEM, the search starts by picking an objective, and it backtraces from the objective to a primary input via the best path. Controllability measures can be used here to determine which path is regarded as the best. Gradually more primary inputs will be assigned logic values. At any time the target fault becomes unexcited or the Dfrontier becomes empty, a bad decision must have been made, and reversal of some previously decisions is needed. The backtracking mechanism proceeds by reversing the most recent decision. If reversing the most recent decision also causes a conflict, the recursive algorithm will continue to backtrack to earlier decisions, until no more reversals are possible, at which time the fault is determined to be undetectable. Three important functions in PODEMRecursion() are getObjective(), backtrace(), and logicSimulate_and_imply(). The getObjective() function returns the next objective the ATPG should try to justify. Before the target fault has been excited, ...
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This note was uploaded on 05/16/2011 for the course ENGINEERIN mp108 taught by Professor Elbarki during the Spring '08 term at Alexandria University.
 Spring '08
 elbarki
 Recursion, Gate

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