Controllability and observability measures for functional-level testability evaluation

An approach of a functional-level testability evaluation, based on controllability and observability measures (c.o.m.), is proposed. Using Rutman´s system model, ordinary applied at the gate level, c.o.m are extended to the data-path level, to permit incorporation of testability constraints in the high-level synthesis stage. The approach of computing these c.o.m. is based on the reduced ordered binary decision diagram (ROBDD) circuit representation. It is shown how to identify untestable parts of a data path and how to evaluate its test cost. The insertion of a two-variable multiplexor, as a structural modification in the data path, is suggested to improve the c.o.m., and so, the test cost. To evaluate the impact of this transformation on the data-path testability, an objective function is proposed, appropriate for high-level synthesis.<>