Signal Representation Assignment for an N - ValueSimulator

In a gate level n-value compiled simulator, the time necessary to propagate a given signal through a gate is of fundamental importance for the speed of the system. This propagation time is minimized when the boolean equations that drive the simulator are minimized. These Boolean equations are generated from the truth tables for AND and OR gates. Therefore there is no unique best assignment for an N-value simulator. If the user is given the opportunity to change the truth tables, as it is common for large N, each time that the truth tables are changed, the value assignment needs to be re-computed, and the basic modules in the libraries regenerated. Since the value assignment problem has combinatorial complexity, an exhaustive search to nd the best assignment is impractical. In this paper we propose a heuristic algorithm that generates a good assignment with complexity O(n 3 log n), where n is the number of values in the simulator. Exhaustive search of 5-value and 8-value simulators was implemented to compare with the results of the algorithm proposed in this paper. This comparison shows that the heuristic is very eecient.