A Continuous-Time Replication Strategy for Efficient Multicast in Asynchronous NoCs

Multicast communication (one-to-many) is common in parallel architectures and emerging areas, such as neuromorphic computing. However, there is very limited research in supporting multicast in asynchronous networks-on-chip (NoCs). This paper proposes a new parallel multicast asynchronous NoC with a 2-D mesh topology. To the best of our knowledge, this is the first general-purpose asynchronous NoC to support multicast in 2-D meshes. A critical feature of this NoC is the use of a new continuous-time replication strategy, where the flits of a multicast packet are routed through the distinct outputs of the router according to each output's own rate, in parallel, and in continuous time. This unique asynchronous continuous-time replication, not discretized to clock cycles, can handle subtle variations in network congestion and exploit “subcycle” differentials in operating speeds. A new continuous-time multiway read (CMR) buffer is proposed to enable this replication strategy. Only a single CMR buffer is used per input port, with multiple independent read pointers, which is accessed by different outputs. For diverse multicast benchmarks, the new parallel multicast network is achieved significant latency and throughput gains over a serial baseline. Interestingly, consistent latency improvements were observed for unicast, in spite of the extra instrumentation.