Untestable Multi-Cycle Path Delay Faults in Industrial Designs

The need for high-performance pipelined architectures has resulted in the adoption of latch based designs with multiple, interacting clocks. For such designs, time sharing across latches results in signals which propagate across multiple clock cycles along paths with multiple latches. These paths need to be tested for delay failures to ensure reliability of performance. However, many of these multi-cycle paths can be untestable and significant computational effort is wasted in targeting such paths during test generation and fault grading. To save this computational effort, a-priori identification of untestable multicycle paths is desired. We address this issue in our paper through a novel and unique framework: unlike traditional techniques, which focus only on single-cycle path delay faults (for flip-flop based designs with single clock), our framework efficiently identifies untestable multi-cycle path delay faults (Mpdfs) in latch-based designs with multiple clocks. We use a novel graphical representation and sequential implications to identify non-robustly untestable M-pdfs through a three-step methodology. Results for industrial designs demonstrate the effectiveness and scalability of our framework.