Synthesis for Logical Initializability of Synchronous Finite State Machines

A new method is introduced for the synthesis for logical initializability of synchronous state machines. The goal is to synthesize a gate-level implementation that is initializable when simulated by a 3-valued (0,1,X) simulator. The method builds on an existing approach of Cheng and Agrawal, which uses constrained state assignment to translate functional initializability into logical initializability. Here, a different state assignment method is proposed which, unlike the method of Cheng and Agrawal, is guaranteed safe and yet is not as conservative. Furthermore, it is demonstrated that certain new constraints on combinational logic synthesis are both necessary and sufficient to insure that the resulting gate-level circuit is 3-valued simulatable. Interestingly, these constraints are similar to those used for hazard-free synthesis of asynchronous combinational circuits. Using the above constraints, we present a complete synthesis for initializability method, targeted to both two-level and multi-level circuits