BOFAR: buffer occupancy factor based adaptive router for mesh NoCs

If the route computation operation in an adaptive router returns more than one output channels, the selection strategy chooses one from them based on the congestion metric used. The effectiveness of a selection strategy depends on what metric is used to identify congestion and how precisely that metric captures the actual congestion. The number of cycles a flit stays in a router is a direct indication of the contention level of the output port it desires to move out. We propose buffer Occupancy Factor based Adaptive Router (BOFAR), wherein the history of cycles spent by flits in buffers is used as the congestion metric. BOFAR outperforms the baseline architectures built on minimal odd-even adaptive router model with conventional selection strategies like count of free downstream virtual channels at reachable neighbors, and fluidity of buffers in downstream neighbors. Our experiments on 4x4 mesh NoC with various synthetic traffic patterns show that BOFAR exceeds the performance of best baseline adaptive router with 21% average and 78% maximum latency reduction at saturation load. The reduced average packet latency, increased buffer fluidity fairness, and increased saturation point of BOFAR with minimal overhead in area, power, and wiring makes it a promising alternative to existing adaptive routers in mesh NoCs.