Optimization of sequential verification by history-based dynamic minimization of BDDs

Binary Decision Diagrams (BDDs) are the state-of-the-art data structure in VLSI CAD, especially in sequential verification tasks, like state-space exploration and image computation. Since their size largely depends on the chosen variable ordering, dynamic variable reordering methods, like sifting, often have to be applied while the BDD is constructed. Usually sifting is called each time a given node limit is reached and it is therefore called frequently during the construction of large BDDs. Often most of the runtime is spent for sifting while the BDD is built. Recently an approach to reduce runtime during BDD construction for combinational circuits by using history-based decision procedures has been proposed. In this paper we show that for sequential circuits different criteria should be used to select the type of sifting that involve knowledge from the sequential domain. The algorithm has been included in VIS. Experimental results show that the overall runtime can be reduced significantly and is also clearly superior to the combinational approach.