184 VLSI Test Principles and Architectures the objective is simply to set the line on which the target fault resides to the value opposite to the stuck value. Once the fault is excited, the getObjective() function selects the best fault-effect from the D-frontier to propagate. The pseudo-code for getObjective() is shown in Algorithm 9. Algorithm 9 getObjective ±C² 1: if fault is not excited then 2: return ±g³ v² ; 3: end if 4: d = a gate in D-frontier; 5: g = an input of d whose value is x ; 6: v = non-controlling value of d ; 7: return ±g³v² ; The backtrace() function returns a primary input assignment from which there is a path of unjustified gates to the current objective. Thus, backtrace() will never traverse through a path consisting of one or more justified gates. From the objec-tive’s point of view, the getObjective() function returns an objective, say g = v , which means the current value of g is “don’t care.” If g were set to v , g = v would have never been selected as an objective, as it conflicts with gate
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