Logical time: specification vs. implementation
ACM SIGSOFT Software Engineering Notes
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All formal hardware verification tools in the market today interpret hardware description languages (HDLs) based on their synthesis semantics. This limits formal verification to synthesizable designs. The result, either a proof or a counterexample, produced by a formal tool can be inconsistent with simulation due to synthesis and simulation mismatches. And finally, conversion from a synthesized gate-level circuit to a formal model such as a Kripke structure or a Mealy machine is complex for designs containing gated clocks or latches. Existing solutions are often based on heuristics rather than language semantics. In this paper, we propose a new approach that constructs formal models based on simulation semantics. We symbolically simulate HDL designs using non-canonical word-level expressions to represent the values of design signals. We show that the formal model is consistent with simulation at specified sample points, which can be chosen to represent a clock cycle or a transaction. Our approach has been implemented in a tool called Simon. Experimental results show that Simon can efficiently construct formal models for large industrial designs.