Provably good global buffering by generalized 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 application specified integrated circuit methodologies. We address the problem of how to perform the buffering of global multiterminal nets given an existing buffer block plan. We give provably good and heuristic algorithms for this problem. The method routes connections using available buffer blocks, such that required upper and lower bounds on buffer intervals are satisfied. In addition, the algorithms allow more than one buffer to be inserted into any given connection and observe upper bounds and parity constraints on the number of buffers per connection. Most importantly, and unlike previous works on the problem, we take into account: 1) multiterminal nets; 2) multiple routing layers; 3) simultaneous buffered routing and compaction; and 4) buffer libraries. Our method outperforms existing algorithms for the problem, based on two-pin decompositions of the nets, and has been validated on top-level layouts extracted from a recent high-end microprocessor design.