RapidRoute: Fast Assembly of Communication Structures for FPGA Overlays

We can implement relocatable, bus-based communication structures on Xilinx FPGAs using RapidWright while delivering competitive frequency, single digit speedups in execution time, and orders of magnitude reduction in memory usage over Xilinx Vivado 2017.2. We develop RapidRoute, a custom router that exploits symmetry in placement and routing of bus endpoints, caching of reusable route segments, selective multi-threading of the router engine, and abutment-friendly tiling heuristics. The key idea is to reduce the amount of work necessary to generate these communication structures through the use of search heuristics, parallelism, and reuse. We are able to outperform Vivado router by as much as 8× for topologies ranging from 1D rings, torii, and meshes, while taking 1000× lower memory footprint, and delivering timing with 0.2ns of Vivado. RapidRoute opens the door to building a family of custom routing tools for constructing FPGA overlays for various application domains.