A study on unroutable placement recognition

Abstract

To avoid producing unroutable placement solutions, many state-of-the-art routability-driven placers iteratively invoke global routers to evaluate their placement solutions and then perform routability optimization. However, using a global router to evaluate hard-to-route placement solutions may spend considerable runtime and it cannot guarantee that a placement is truly unroutable to any router. This paper presents an unroutable placement recognizer based on a window-based layout scanning algorithm, which can confirm some placements that are exactly unroutable among a set of hard-to-route placements. In addition, if a placement is recognized to be unroutable, the recognizer can point out unroutable regions and report a lower bound of total overflow for the placement. The experimental results reveal that the proposed recognizer can find out 16 placements that are definitely unroutable among 23 widely used hard-to-route global routing benchmarks.