An Event-Driven Model for the SpiNNaker Virtual Synaptic Channel

Neural networks present a fundamentally different model of computation from conventional sequential hardware, making it inefficient for very-large-scale models. Current neuromorphic devices do not yet offer a fully satisfactory solution even though they have improved simulation performance, in part because of fixed hardware, in part because of poor software support. SpiNNaker introduces a different approach, the "neuromimetic" architecture, that maintains the neural optimisation of dedicated chips while offering FPGA-like universal configurability. Central to this parallel multiprocessor is an asynchronous event-driven model that uses interrupt-generating dedicated hardware on the chip to support real-time neural simulation. In turn this requires an event-driven software model: a rethink as fundamental as that of the hardware. We examine this event-driven software model for an important hardware subsystem, the previously-introduced virtual synaptic channel. Using a scheduler-based system service architecture, the software can "hide" low-level processes and events from models so that the only event the model sees is "spike received". Results from simulation on-chip demonstrate the robustness of the system even in the presence of extremely bursty, unpredictable traffic, but also expose important model-level tradeoffs that are a consequence of the physical nature of the SpiNNaker chip. This event-driven subsystem is the first component of a library-based development system that allows the user to describe a model in a high-level neural description environment and be able to rely on a lower layer of system services to execute the model efficiently on SpiNNaker. Such a system realises a general-purpose platform that can generate an arbitrary neural network and run it with hardware speed and scale.