Design tradeoffs for hard and soft FPGA-based Networks-on-Chip

Incorporating Networks-on-Chip (NoC) within FPGAs has the potential not only to improve the efficiency of the interconnect, but also to increase designer productivity and reduce compile time by raising the abstraction level of communication. By comparing NoC components on FPGAs and ASICs we quantify the efficiency gap between the two platforms and use the results to understand the design tradeoffs in that space. The crossbar has the largest FPGA vs. ASIC gaps: 85× area and 4.4× delay, while the input buffers have the smallest: 17× area and 2.9× delay. For a soft NoC router, these results indicate that wide datapaths, deep buffers and a small number of ports and virtual channels (VC) are favorable for FPGA implementation. If one hardens a complete state-of-the-art VC router it is on average 30× more area efficient and can achieve 3.6× the maximum frequency of a soft implementation. We show that this hard router can be integrated with the soft FPGA interconnect, and still achieve an area improvement of 22×. A 64-node NoC of hard routers with soft interconnect utilizes area equivalent to 1.6% of the logic modules in the latest FPGAs, compared to 33% for a soft NoC.