Power and Performance Efficient Partial Circuits in Packet-Switched Networks-on-Chip

In this paper, we propose a hybrid packet-circuit switching for networks-on-chip to benefit from the advantages of both switching mechanisms. Integrating circuit and packet switching into a single NoC is achieved by partitioning the link bandwidth and router data-path and control-path elements into two parts and allocating each part to one of the switching methods. In this NoC, during injection in the source node, packets are initially forwarded on the packet-switched sub-network, but keep requesting a circuit towards the destination node. The circuit-switched part, at each cycle, collects the circuit construction requests, performs arbitration among the conflicting requests, and constructs circuits over the unallocated circuit-switched sub-network links. Unlike traditional circuit-switching, the circuit end point in this NoC is not necessarily the packet destination, rather the circuits can be terminated in any intermediate node between the packet source and destination nodes. At that node, the packet may either travel over another circuit (in case of successful circuit request) or continue its path over the packet-switched part. Therefore, packets may switch between the two sub-networks several times during their life-time in the network. Circuit construction is handled by a low-latency and low-cost setup network. To keep the complexity of the circuit construction low, the circuits are restricted to span within a neighborhood of d hops of the requesting node. The experimental results show considerable improvement in energy and latency over a traditional packet-switched NoC.