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Optimizing for routability during FPGA placement is becoming increasingly important, as failure to spread and resolve congestion hotspots throughout the chip, especially in the case of large designs, may result in placements that either cannot be routed or that require the router to work excessively hard to obtain success. In this article, we introduce a new, analytic routability-aware placement algorithm for Xilinx UltraScale FPGA architectures. The proposed algorithm, called GPlace3.0, seeks to optimize both wirelength and routability. Our work contains several unique features including a novel window-based procedure for satisfying legality constraints in lieu of packing, an accurate congestion estimation method based on modifications to the pathfinder global router, and a novel detailed placement algorithm that optimizes both wirelength and external pin count. Experimental results show that compared to the top three winners at the recent ISPD’16 FPGA placement contest, GPlace3.0 is able to achieve (on average) a 7.53%, 15.15%, and 33.50% reduction in routed wirelength, respectively, while requiring less overall runtime. As well, an additional 360 benchmarks were provided directly from Xilinx Inc. These benchmarks were used to compare GPlace3.0 to the most recently improved versions of the first- and second-place contest winners. Subsequent experimental results show that GPlace3.0 is able to outperform the improved placers in a variety of areas including number of best solutions found, fewest number of benchmarks that cannot be routed, runtime required to perform placement, and runtime required to perform routing.

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Effectively estimating and managing congestion during placement can save substantial placement and routing runtime. In this article, we present a machine-learning model for accurately and efficiently estimating congestion during FPGA placement. Compared with the state-of-the-art machine-learning congestion-estimation model, our results show a 25% improvement in prediction accuracy. This makes our model competitive with congestion estimates produced using a global router. However, our model runs, on average, 291× faster than the global router. Overall, we are able to reduce placement runtimes by 17% and router runtimes by 19%. An additional machine-learning model is also presented that uses the output of the first congestion-estimation model to determine whether or not a placement is routable. This second model has an accuracy in the range of 93% to 98%, depending on the classification algorithm used to implement the learning model, and runtimes of a few milliseconds, thus making it suitable for inclusion in any placer with no worry of additional computational overhead.