Reclaiming over-the-IP-block routing resources with buffering-aware rectilinear Steiner minimum tree construction

Abstract

In this paper, we study an often overlooked but very important and practical problem of building Buffering-aware Over-the-Block rectilinear Steiner minimum tree (BOB-RSMT). In most previous works, the routing resources over the IP blocks were simply treated as routing blockages, resulting in significant waste of routing resources on higher metal layers not utilized by internal intra-block routing. On the other hand, routing over large IP blocks needs special attention as there is no way to insert buffers inside hard IP blocks, which can lead to unresolvable slew/timing violations. In this paper, we propose a novel BOB-RSMT algorithm which helps reclaim the "wasted" over-the-block routing resources while meeting user-specified slew constraints. Our algorithm incrementally and efficiently migrates initial tree structures with buffering-awareness to meet slew constraints while minimizing wire length. It can handle complex blocks including rectilinear shapes. Our experiments on various benchmarks demonstrate very promising results. By utilizing over-the-block routing resources intelligently, we can save the outside-block wire length as well as the total wire length significantly compared with the conventional obstacle-avoiding rectilinear Steiner minimum tree (OA-RSMT) algorithms. BOB-RSMT also reduces the repeater count/area needed to satisfy slew constraints, which is very important for modern design closure.