Synthesis of hazard-free multilevel logic under multiple-input changes from binary decision diagrams

Abstract

We describe a new method for directly synthesizing a hazard-free multilevel logic implementation from a given logic specification. The method is based on free/ordered Binary Decision Diagrams (BDD's), and is naturally applicable to multiple-output logic functions. Given an incompletely-specified (multiple-output) Boolean function, the method produces a multilevel logic network that is hazard-free for a specified set of multiple-input changes. We assume an arbitrary (unbounded) gate and wire delay model under a pure delay (PD) assumption, we permit multiple-input changes, and we consider both static and dynamic hazards under the fundamental-mode assumption. Our framework is thus general and powerful. While it is not always possible to generate hazard-free implementations using our technique, we show that in some cases hazard-free multilevel implementations can be generated when hazard-free two-level representations cannot be found. This problem is generally regarded as a difficult problem and it has important applications in the field of asynchronous design. The method has been automated and applied to a number of examples. >