| Summary: | 博士 === 國立交通大學 === 資訊科學與工程研究所 === 101 === Routability has become one of most critical issues to successfully achieve design closure. To address this issue, global routing plays an important role in the placement and routing flow. During the placement stage, a fast global router can serve as a routing congestion estimator to guide that placers improve the routability of placement solutions; however, traditional global routers are too slow to offer quick but accurate congestion estimation. In the routing stage, the duty of a global router is to identify a global routing result to guide downstream detailed routers. The runtime of the detailed router can significantly reduce if the global routing result has well optimized congestion and wirelength.
In this dissertation, two global routing engines are proposed, Grace and NCTU-GR 2.0. Grace is a fast global router to serve as a fast routing congestion estimator, adopts the proposed unilateral monotonic routing and hybrid unilateral monotonic routing to replace time-consuming maze routing in its routing flow, and invokes a congestion-aware bounding box expansion scheme to avoid over-expanding the searching regions to achieve high speedup. Moreover, in order to use Grace in the industrial flow, Grace have been enhanced to tackle the layer directive and scenic constraints for considering the timing issue.
Another proposed global router NCTU-GR 2.0 can generate high-quality global routing results to guide the downstream detailed router. The proposed bounded-length maze routing avoids producing redundant detours to save routing resource; rectilinear Steiner minimum tree aware routing scheme can guide NCTU-GR 2.0 to build a routing tree for each multi-pin net with shorter wirelength; a dynamically adjusted history cost function highlights for NCTU-GR 2.0 which grid edges are critical routing resource that can be more carefully allocated to the nets that really desire. Based on the proposed innovations to carefully utilize routing resource, NCTU-GR 2.0 obtains shorter total wirelength and lower congestion than the other state-of-the-art academic global routers.
In addition, between the placement and routing stages, this dissertation presents an incremental place-and-route tool called Ropt to optimize the routability of a given placement solution. Rather than minimizing HPWL, Ropt directly improves routability by minimizing the routing cost of nets, as the routing cost is defined in terms of global congestion, local congestion and wirelength. In addition to using NCTU-GR 2.0 to evaluate the routability of the placement solutions, this work also uses Wroute to obtain detailed routing results of the optimized placement solutions for the evaluation of real routability.
Finally, the proposed post-3D-global-router called Post3DGR further refines the wirelength, congestion, and via count of a given 3D global routing result. Post3DGR consists of the 3D post routing stage and negotiation-based layer assignment stage. The 3D post routing stage adopts an inherited history cost function to guide the routing, which can greedily reduce total wirelength and vias. The negotiation-based layer assignment stage re-assigns the routing layer for each wire to reduce via count. The negotiation-based layer assignment can be extended to consider via overflow and antenna effect. Considering these issues before detailed routing can ease the effort and runtime of subsequent detailed routing.
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