Low power flitwise routing in an unidirectional torus with minimal buffering

State-of-the-art Network on Chips (NoCs) provide a high throughput and low latency by sending packets of data through a mesh topology, using virtual channels and wormhole flow control. The downside of this technology is a high area and energy consumption due to many buffers, large crossbars and a complex arbitration logic within the routers.

In our approach, we avoid flow control and complex analysis of the head flit by sending single standalone flits instead of large packets of flits. As the order of flits is preserved between sending and receiving node, large data blocks can be sent anyway. The complexity of the router is further reduced by using an unidirectional 2D torus instead of a mesh, which reduces the number of router ports from 5 to 3. The flits are X-Y-routed and transported bufferless, as long as they stay within one dimension. Consequently there is only one FIFO per router, which buffers flits when they turn from X to Y direction. In terms of throughput and latency the so-called paternoster router is comparable with a conventional router with two virtual channels, but it consumes 50% less energy and 60% less area.