toward formalizing a validation methodology using simulation coverage
The biggest obstacle in the formal verification of large designs istheir very large state spaces, which cannot be handled even bytechniques such as implicit state space traversal. The only viablesolution in most cases is validation by functional simulation. Unfortunately, this has the drawbacksof high computationalrequirementsdue to the large number of test vectors needed, and the lack of adequate coverage measures to characterize the quality of a given testset. To overcome these limitations, there has been recent interest inhybrid techniques which combine the strengths of formal verification and simulation. Formal verification-based techniques are usedon a test model (usually much smaller than the design) to derive a setof functional test vectors, which are then used for design validationthrough simulation. The test set generated typically satisfies somecoverage measure on the test model. Recent research has proposedthe use of state or transition coverage. However, no effort has beenmade to relate these measures to the coverage of design errors. Furthermore, the derivation of the test model remains largely ad-hoc,with few formal guidelines.We demonstrate that under a given set of assumptions, transitiontours on test models can be used for complete validation of an implementation against a specification, for a large and important classof designs that includes many programmable/hardwired, general-purpose processors/DSPs. A by-product of this study is specificguidelines for deriving the test model, motivated by the requirement of providing complete coverage of all errors. We illustrate theapplication of our methodology on a pipelined implementation of the DLX processor.
formalism methodology use simulation coverage formal verification design space functional requirements test vectorization measurement quality model functional testing general research transit errors guideline demonstrate completeness implementation programmer processor pipeline product ad-hoc