On wirelength estimations for row-based placement

Wirelength estimation in very large scale integration layout is fundamental to any predetailed routing estimate of timing or routability. In this paper, we develop efficient wirelength estimation techniques appropriate for wirelength estimation during top-down floorplanning and placement of cell-based designs. Our methods give accurate, linear-time approaches, typically with sublinear time complexity for dynamic updating of estimates (e.g,, for annealing placement). Our techniques offer advantages not only for early on-line wirelength estimation during top down placement, but also for a posteriori estimation of routed wirelength given a final placement. In developing these new estimators, we have made several contributions, including 1) insight into the contrast between region-based and bounding box-based rectilinear Steiner minimal tree (RStMT) estimation techniques; 2) empirical assessment of the correlations between pin placements of a multipin net that is contained in a block; and 3) new wirelength estimates that are functions of a block's complexity (number of cell instances) and aspect ratio.