262_pdfsam_VLSI TEST PRINCIPLES & ARCHITECTURES

262_pdfsam_VLSI TEST PRINCIPLES & ARCHITECTURES -...

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Unformatted text preview: Test Generation 231 a case in which the deterministic ATPG successfully finds a sequence for at least one fault. The fitness functions for the three separate stages of ALT-TEST depend on a vari- ety of parameters. Because each stage targets a different goal, the set of parameters that control the search will differ as well. The parameters that can affect the fitness of an individual include the following: P 1 —Number of faults detected P 2 —Number of flip-flops to which fault effects have arrived P 3 —Number of new states visited P 4 —Number of flip-flops set to their difficult-to-control values It can be seen that parameters P 3 and P 4 contribute to the expansion of the searched state space. While P 3 explicitly aims for visitation of more states, P 4 guides the search by favoring sequences that are able to set the difficult-to-control flip-flops to values that have not yet been encountered. Consequently, a new state is likely to be visited. All four parameters are given different weights across the three stagesbe visited....
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