HAZARD-FREE IMPLEMENTATION OF SPEED-INDEPENDENT CIRCUITS

This paper develops a theoretical framework for the hazard-free gate-l evel implementation of speed-independent circuits specified by event-b ased models, such as signal transition graphs (for processes with AND causality and input choice) or their extension, called change diagrams (which allow err-causality). It presents sufficient conditions, calle d the generalized monotonous cover requirements, for a hazard-free cir cuit to be built within a standard implementation structure. This stru cture consists of two-level simple-gate combinational logic and a row of latches, either a C-element or an RS-latch, A set of semantic-prese rving transformations is defined that can be applied to an original be havioral description of the circuit so as to produce its specification in the form that satisfies the monotonous cover requirement. The tran sformations are applied at the event-based representation level (to av oid state explosion) and proved to be effective, The main result of th e paper is therefore twofold: 1) the proof that any speed-independent behavior can be implemented at the gate level without hazards and 2) a n efficient method for constructing such an implementation, Experiment al results show that the proposed method compares very favorably, in a rea and performance, to the previously known techniques.