Interaction among cost functions in placement

Abstract

In this paper, we focus on the physical design problems and their interaction with higher- and lower-levels. We propose to study the interaction between various cost functions in placement. In particular, we will consider, net-cut, wire-length, congestion, and timing. We show that minimizing wire-length may (and in general, will) create locally congested regions. We demonstrate that most other congestion related objectives are ill behaved and they should only be used in a post processing step. Using a post processing stage is found to be more effective than optimizing the congestion in one step. For the relationship between wire-length and net-cut, we demonstrate that they are correlated differently in different hierarchical levels.