Partial scan delay fault testing of asynchronous circuits

Asynchronous circuits operate correctly only under timing assumptions. Hence testing those circuits for delay faults is crucial. The paper describes a three step method to detect possible delay faults in a sequential asynchronous circuit. The delays that are to be tested must be provided by the synthesis system. By using this information a set of paths in the circuit that must be tested is identified (step 1). For these paths the circuit is made acyclic by inserting at least one scan latch in every cycle (step 2). Then test patterns are generated for these paths (step 3). These test patterns consist of setup and initialization vectors and the final test vector. We provide effective procedures to solve both the initialization and the test pattern generation problem. The latter problem is solved by reduction to a classical problem of stuck-at test pattern generation for a related combinational circuit. Finally, a heuristic is proposed to determine which state variables must become part of a scan chain, or for which input variables the positive and negative phase must be driven independently in test mode. Experimental results shows that a high level of path delay fault testability can be achieved with partial scan.