Steep coverage-ascent directed test generation for shared-memory verification of multicore chips

This paper proposes a framework for functional verification of shared memory that relies on reusable coverage-driven directed test generation. It reveals a new mechanism to improve the quality of non-deterministic tests. The generator exploits general properties of coherence protocols and cache memories for better control on transition coverage, which serves as a proxy for increasing the actual coverage metric adopted in a given verification environment. Being independent of coverage metric, coherence protocol, and cache parameters, the proposed generator is reusable across quite different designs and verification environments. We report the coverage for 8, 16, and 32-core designs and the effort required for exposing nine different types of errors. The proposed technique was always able to reach similar coverage as a state-of-the-art generator, and it always did it faster above a certain threshold. For instance, when executing tests with IK operations for verifying 32-core designs, the former reached 65% coverage around 5 times faster than the latter. Besides, we identified challenging errors that could hardly be found by the latter within one hour, but were exposed by our technique in 5 to 30 minutes.