The Physical Design of On-Chip Interconnections: Part I: Quantification of Custom Interconnections

Custom interconnect design complements automated route algorithms which do not guarantee the
generation of robust, legal routes for all signals in a ULSI design. Intervention with custom intercon-
nections stabilizes a route solution and reduces time required to route follow-on designs with logic and
floorplan changes. Implementation of custom interconnects is a highly skilled art. In general, the tools
available to the designer do not evaluate the quality of the inserted custom interconnections, and success is predicated only on the production of a legal design within a pre-specified time. It is desirable to have criteria to select signals for custom interconnections and to evaluate whether or not intervention with custom interconnections for these signals is effective in improving physical properties of these signal routes without adversely affecting physical properties of the remaining signal routes. This paper, the first in a series, presents a self-consistent formalism of intervention with custom interconnections, the addition of custom interconnections to a physical design, and the quantification of overall interconnection quality. The analytical techniques presented in this series of papers can be also incorporated in semi-custom and ASIC designs and may serve as tools to evaluate and improve various route algorithms.