Reducing Wire and Energy Overheads of the SMART NoC Using a Setup Request Network

Network-on-chip (NoC), due to its superior scalability, has become increasingly popular in multicore and many-core designs. A recent state-of-The-Art NoC design, called single-cycle multihop asynchronous repeated traversal (SMART), enables ultralow latency performance by enabling a flit to bypass the pipelines of intermediate routers entirely. This enables a flit to traverse multiple routers within a single clock cycle. However, there are two concerns related to SMART: 1) it employs dedicated broadcast wires to transmit SMART-hop setup requests (SSRs), incurring large wire and energy overheads and 2) it needs a complex allocator to arbitrate multiple simultaneous SSRs. In this paper, we propose an SSR network to address these two concerns. This is a specialized network that replaces long and overlapping broadcast wires with shorter wires and switches. It reduces the wire and energy overheads significantly. It also eliminates low-priority SSRs before they reach the allocator and, therefore, leads to a simplified allocator design. We evaluate SSR networks in various contexts. Our evaluation demonstrates that the SSR network can reduce the wire overhead by up to 12.2×. Moreover, it results in up to 63.7% area reduction, and up to 15.7% dynamic energy reduction. It also makes multiple physical networks and/or wider flits feasible. This paper shows that with fewer wires and the same amount of buffer space, multiple simple SMART-1D networks can deliver a higher bandwidth and lower latency than a single complex SMART-2D network, when our SSR network is used.