HOL-MDG : A Hybrid Tool for Formal Verification

Formal verification methods fall in one of three categories: theorem proving, decision diagrams based methods and symbolic simulation. In this work, we focus on combining the first two categories. In theorem proving methods, the design’s behavior as well as its structure are described in some formal logic. Then the design structure is proved to conform to the expected behavior using a set of axioms and inference rules. Theorem provers generally provide very powerful reasoning and abstraction mechanisms. This makes it possible to deal with complex designs. Nevertheless, theorem provers require a deep understanding of their underlying logic. They also involve a lot of interactions with the user. Decision diagrams based tools include equivalence and model checkers. These tools are easy to use since the verification is performed automatically. However, they fail to verify complex designs due to the state explosion problem. Therefore, combining both categories should enable verifying complex designs with much less interaction with the verification tool. Another way to cope with complex designs is to apply a hierarchical verification approach. In such an approach, the design consists of a block hierarchy. Individual blocks are verified separately, then their correctness results are combined to verify the next level blocks.