Fast and Coherent Simulation with Zero Delay Elements

This paper addresses the problem of event-directed logic simulation with part of the elements having zero delay. Incoherences arising from spikes having null duration (i.e., multiple transitions of a signal at a given simulation time, due to the simulation algorithm) are solved by a Two-Pass procedure, combining levelizing and event-driven simulation and yielding Ordered Activity Propagation. To overcome the speed degradation with respect to One-Pass simulation, a variation of the usual Two-Pass technique, termed Predictor/Corrector, is introduced at the gate level. Ordered Activity Propagation is also beneficial to concurrent multilevel simulation.