Sequential logic path delay test generation by symbolic analysis

Many test generation algorithms for path delay faults assume a special methodology for application of the test sequence. The two-vector test sequences are valid under the assumption that the combinational logic reaches a steady state following the first vector before the second vector is applied. While such vectors may be acceptable for combinational circuits, their use for testing a non-scan sequential circuit is virtually impossible where it is difficult to run the clock at a constant rate. Most multi-valued algebras for combinational circuits are rendered invalid when vectors are applied at the rated speed. We present a new multi-valued algebra and a test generation algorithm to derive tests for a uniform rated speed test application methodology. The main ideas in the paper include an algebra that derives three-vector test sequences combinational logic and (2) a value propagation rule for latches, resulting in more realistic fault coverages in sequential circuits when all vectors are applied at the rated speed. The test generator uses Boolean functions to reason about state transitions in sequential machines. These Boolean functions are stored and manipulated as Binary Decision Diagrams (BDDs). Experimental data on moderate size ISCAS89 benchmarks are included.