CLASSIC: An O(n(2))-heuristic algorithm for microcode bit optimization based on incompleteness relations

Abstract

This paper presents a heuristic algorithm called CLASSIC for the minimization of the control memory width in microprogrammed processors or the instruction memory width of application-specific VLIW (Very Long Instruction Word) processors. CLASSIC results in nearly optimal solutions with the time complexity of O(n(2)), where n denotes the number of microoperations. In this paper, we also propose the so-called incompleteness relations which are exploited for the minimization of the control memory width. Experiments using various examples have shown that CLASSIC always achieves smaller microprogram widths compared to the earlier techniques based on the maximal compatibility class or the minimal AND/OR set. The results show that CLASSIC can reduce the control memory width by 34.2% on average compared with a heuristic compatibility class algorithm.