DUNE-a multilayer gridless routing system

Advances of very large scale integration technologies present two challenges for routing problems: 1) the higher integration of transistors due to shrinking of featuring size and 2) the requirement for off-grid routing due to the variable-width variable-spacing design rules imposed by optimization techniques. In this paper, we present a multilayer gridless detailed routing system for deep submicrometer physical designs. Our detailed routing system users a hybrid approach consisting of two parts: 1) an efficient variable-width variable-spacing detailed routing engine and 2) a wire-planning algorithm providing high-level guidance as well as ripup and reroute capabilities. Our gridless routing engine is based on an efficient point-to-point gridless routing algorithm using an implicit representation of a nonuniform grid graph. We proved that such a graph guarantees a gridless connection of the minimum cost in multilayer variable-width and variable-spacing routing problem. A novel data structure using a two-level slit tree plus interval tree in combination of cache structure is developed to support efficient queries into the connection graph. Our experiments show that this data structure is very efficient in memory usage while very fast in answering maze expansion related queries. Our detailed routing system also features a coarse grid-based wire-planning algorithm that uses exact gridless design rules (variable-width and variable-spacing) to accurately estimate the routing resources and distribute nets into routing regions. The wire-planning method also enables efficient ripup and reroute in gridless routing. Unlike previous approaches for gridless routing that explore alternatives of blocked nets by gradually tightening the design rules, our planning-based approach can take the exact gridless rules and resolve the congestion and blockage at a higher level. Our experimental results show that using the wire-planning algorithm in our detailed routing system can improve the routability and also speed up the runtime by 3 to 17 times.