Abstract-Bluehive is a custom 64-FPGA machine targeted at scientific simulations with demanding communication requirements. Bluehive is designed to be extensible with a reconfigurable communication topology suited to algorithms with demanding high-bandwidth and low-latency communication, something which is unattainable with commodity GPGPUs and CPUs. We demonstrate that a spiking neuron algorithm can be efficiently mapped to Bluehive using Bluespec SystemVerilog by taking a communication-centric approach. This contrasts with many FPGA-based neural systems which are very focused on parallel computation, resulting in inefficient use of FPGA resources. Our design allows 64k neurons with 64M synapses per FPGA and is scalable to a large number of FPGAs.

Managing the memory wall is critical for massively parallel FPGA applications where data-sets are large and external memory must be used. We demonstrate that a soft vector processor can efficiently stream data from external memory whilst running computation in parallel. A non-trivial neural computation case study illustrates that multi-core vector processing coupled with careful layout of data structures performs similarly to an elaborate full-custom memory controller and execution pipeline. The vector processing version was far simpler to code so we encourage others to consider vector machines before contemplating a full-custom architecture on FPGA.

We demonstrate that a small library of customizable interconnect components permits low-area, high-performance, reliable communication tuned to an application, by analogy with the way designers customize their compute. Whilst soft cores for standard protocols (Ethernet, RapidIO, Infiniband, Interlaken) are a boon for FPGA-to-other-system interconnect, we argue that they are inefficient and unnecessary for FPGA-to-FPGA interconnect. Using the example of BlueLink, our lightweight pluggable interconnect library, we describe how to construct reliable FPGA clusters from hundreds of lower-cost commodity FPGA boards. Utilizing the increasing number of serial links on FPGAs demands efficient use of soft-logic, making domainoptimized custom interconnect attractive for some time to come.

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