Extending microcode compaction for real architectures

Abstract

Microcode compaction is an essential component of any high-level language compiler that generates microcode for a horizontal architecture machine. Recent research into both local and global compaction has assumed the use of a simple abstract machine. Although this assumption simplifies the effort considerably, it neglects addressing and timing problems brought on by the uncommon operation of some machines.This paper discusses both local and global compaction in terms of the Burroughs D-machine. The D-machine has peculiar timing and an uncommon jump instruction that do not readily fit into proposed compaction algorithms. Methods for handling these problems are presented. In addition, two popular algorithms for performing compaction, list scheduling and trace scheduling, are explained entirely in terms of the D-machine. This should aid the reader in understanding the problem and evaluating any alternatives.