Provably good global buffering by multiterminal multicommodity flow approximation

To implement high-performance global interconnect without impacting the placement and performance of existing blocks, the use of buffer blocks is becoming increasingly popular in structured-custom and block-based ASIC methodologies. Recent works by Cong, Kong and Pan (1999) and Tang and Wong (2000) give algorithms to solve the buffer block planning problem. In this paper, we address the problem of how to perform buffering of global multiterminal nets given an existing buffer block plan. We give a provably good algorithm based on a recent approach of Garg and Konemann (1998) and Fleischer (1999) [see also Albrecht (2000) and Dragan et al. (2000)]. Our method routes connections using available buffer blocks, such that required upper and lower bounds on buffer intervals-as well as wirelength upper bounds per connection-are satisfied. In addition, our algorithm allows more than one buffer to be inserted into any given connection and observes buffer parity constraints. Most importantly, and unlike previous works on the problem, we take into account multiterminal nets. Our algorithm outperforms existing algorithms for the problem, which are based on 2-pin decompositions of the nets. The algorithm has been validated on top-level layouts extracted from a recent high-end microprocessor design.