A synthesis-agnostic behavioral fault model for high gate-level fault coverage

Early design space exploration is a practice for avoiding issues that manifest themselves at late design phases. Nevertheless, the test development has traditionally been postponed to the final stages of the design process. At the same time, more and more IP designs are sold at the RTL, where details of exact gate-level implementation are unknown. While a range of RTL ATPG methods has been developed over the past decades, the fault models are too inaccurate in order to guarantee full coverage for the gate-level faults. This paper fills the gap by proposing a synthesis-agnostic ATPG based on extending behavioral fault models in order to allow targeting stuck-at faults in the gate-level implementations of RTL designs regardless of the synthesis decisions made. Moreover, the approach does not require adding scan paths and therefore the obtained test sequences serve as at-speed, functional mode tests. Experiments on a set of benchmarks and an industrial design show that the proposed fault models are superior to the previous approaches in terms of stuck-at fault coverage. Comparison with a state-of-the-art gate-level sequential ATPG show higher or equal coverage for the proposed technique achieved at shorter runtimes.