Exploring The Impact Of Switch Arity On Butterfly Fat Tree Fpga Nocs

Overlay Networks-on-Chip (NoCs) for FPGAs based on the Butterfly-Fat Tree (BFT) topology with lightweight flow control deliver low LUT costs and features such as in-order delivery and livelock freedom. BFT NoCs make it possible to conFigure network bandwidth to match application requirements, by choosing switch types with different numbers of ports (arity) for the layers of the tree hierarchy. We increase the design space of BFT NoC configurations available to designers by constructing networks with larger arity-4 switches, in addition to the arity2 switches explored by previous works. When synthesized for the Xilinx UltraScale + VU9P FPGA, our proposed BFT NoCs consume 38-45% fewer LUTs and 33-50% smaller wiring lengths than arity-2 BFT NoCs with the same Rent parameter, in exchange for a reduction in maximum clock frequency in up to 25%. We simulate the operation of our proposed NoCs when routing various real-world workloads with 64 network clients, and show that they consistently achieve better Throughput / LUT cost ratios, when compared to arity-2 BFT NoCs with the same Rent parameter, with improvements of 15 to 120% depending on the benchmark and NoC topology.