Direct Search Procedure for Functional Compaction With Improved Fault Coverage

An important component of ensuring system reliability is the application of functional tests. Functional test sequences are available after simulation-based design verification, they can be extracted from application programs, or generated for target faults. Functional test sequences can be long, and test compaction at the gate-level is important for reducing the test application time without losing fault coverage. Experimental results with several test compaction procedures indicate that test compaction sometimes leads accidentally to an increased fault coverage. Such an increase was observed recently with a gate-level test compaction procedure that has the unique property of restoring functional operation conditions after parts of a sequence are eliminated. The contribution of this article is to use this property of the test compaction procedure to increase the fault coverage directly, in a targeted manner, while compacting the sequence. Experimental results for benchmark circuits in an academic environment demonstrate a significant fault coverage increase combined with significant test compaction.