Synthesis heuristics for large asynchronous sequential circuits
"Many well-known synthesis procedures for asynchronous sequential circuits produce minimal or near-minimal results, but are practical only for very small problems. These algorithms become unwieldy when applied to "large" circuits with, for example, three or more input variables and twenty or more internal states. New heuristic procedures are described which permit the synthesis of very large machines. Although the resulting designs are generally not minimal, the heuristics are able to produce near-minimal solutions orders of magnitude more rapidly than the minimal algorithms. A method for specifying sequential circuit behavior is presented. Input-output sequences define submachines or modules. When properly interconnected, these modules form the required sequential circuit. It is shown that the waveform and interconnection specifications may easily be translated into flow table form. A large flow table simplification heuristic is developed. The algorithm may be applied to tables having hundreds of rows, and handles both normal and non-normal mode circuit specifications. Nonstandard state assignment procedures for normal, fundamental mode asynchronous sequential circuits are examined. An algorithm for rapidly generating large flow table internal state assignments is proposed. The algorithms described have been programmed in PL/1 and incorporated into an automated design system for asynchronous circuits; the system also includes minimum and near-minimum variable state assignment generators, a code evaluation routine, a design equation generator, and two Boolean equation simplification procedures. Large sequential circuits designed using the system illustrate the utility of the heuristic procedures"--Abstract, pages ii-iii.
Missouri University of Science and Technology
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