Methodologies for Diagnosis of Unreachable States via Property Directed Reachability

In the modern design cycle, substantial manual effort is required to correct failed liveness properties due to the limited availability of automated tools. To address this limitation, this paper introduces two techniques to diagnose register transfer level errors that manifest in the form of erroneously unreachable states, which represent a common form of liveness property failure. The first uses steps of reachable state-space over-approximation and traditional debugging to compute a subset of the solutions that make a target state reachable. The second solves a series of unbounded model checking problems using an enhanced model of the circuit's transition relation to compute the complete solution set to the problem. The proposed techniques are complementary to each other and present the user with a configurable tradeoff between runtime and resolution of the returned solution set. Empirical results on OpenCores and HWMCC'15 circuits confirm the effectiveness of the approaches and demonstrate the tradeoffs between them.