The main thrust of the above paper1appears to be a detailed restatement of the "left-edge algorithm" [1], [2] for channel routing. This algorithm is almost a decade old and is now quite familiar to most workers in the field of LSI design automation. That the authors did not reference this earlier work, and devoted much of their paper to a reexposition certainly detracts from its usefulness.

This paper describes an automatic string placement program used to reorder cells in polycell rows such that channel routing in the adjacent channels (a) is not blocked by cyclic constraints, and (b) needs fewer routing tracks. The program utilizes cell reflections and pairwise neighbor exchanges, simultaneously monitoring both the channels immediately above and below the row being reordered. Reductions of 25% in the number of required routing tracks are commonly obtained.

LTX is a minicomputer-based design system for large-scale integrated circuit chip layout which offers a flexible set of interactive and automatic procedures for translating a circuit connectivity description into a finished mask design. The system encompasses algorithms for two-dimensional placement, string placement, exploitation of equivalent terminals, decomposition of routing into channels, and channel routing. Circuit connectivity is preserved during interactive procedures. LTX runs on an H-P 2100 series computer with 32K of memory and disc.