Random Test Generation With Input Cube Avoidance

Test generation procedures attempt to assign values to the inputs of a circuit so as to detect target faults. We investigate a complementary view whereby the goal is to avoid the assignment of certain input values in order not to prevent faults from being detected. We describe a procedure for computing input cubes (or incompletely specified input vectors) that should be avoided during test generation for target faults. We demonstrate that avoiding such input cubes leads to the detection of target faults after the application of limited numbers of random input vectors. This indicates that explicit test generation is not necessary once certain input values are precluded. Other potential uses of the computed input cubes are in a deterministic test generation procedure to reduce the search space, and during built-in test generation to preclude input vectors that will not lead to the detection of target faults. We consider stuck-at faults in full-scan circuits. We also extend the discussion to four-way bridging faults.