Lanterna Rally

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Published: 2012

Total Pages: 0

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RETHINKING GLOBAL ROUTING FOR MODERN VLSI DESIGN: CONGESTION REDUCTION AND MULTI-OBJECTIVE OPTIMIZATION Hamid Shojaei Under the supervision of Professor Azadeh Davoodi At the University of Wisconsin-Madison The high volume and complexity of cells and interconnect structures are causing serious challenges to routability in modern VLSI design. Several new factors contribute to routing congestion including significantly-different wire size and spacing among the metal layers, sizes of inter-layer vias, various forms of routing blockages, local congestion due to pin density and wiring inside a global-cell, and virtual pins located at the higher metal layers. In addition, interconnects now play a significant role in impacting the performance metrics of a design including power, speed and area. Global routing, as the first stage in which the interconnects are planned, is now of significant importance in determining the performance metrics and the routability of the design. However, the standard model of global routing considers minimization of wirelength with a simplified model of routing resources which ignores these objectives and complicating factors. To address the above challenges, this dissertation has three contributions in rethinking global routing for modern VLSI design. First, we present a framework for congestion analysis for quick prediction of the locations of highly-utilized routing regions. The fast framework is suitable for integration in the design flow, for example as an integration within a routability-driven placement procedure. Second, we offer two contributions in order to estimate and manage the congestion caused by local nets which are ignored in a standard model of global routing. It allows optimizing congestion directly within global routing by treating global and detailed routing in a more holistic manner. In addition, many of the above-mentioned factors contributing to congestion are accounted for in our congestion analysis and optimization framework. Finally, we present a procedure for multi-objective global routing which is able to optimize multiple performance metrics beyond wirelength. The framework is a collaborative one which receives as input multiple global routing solutions created by single-objective procedures.