Trade-offs in the design of a router with both guaranteed and best-effort services for networks on chip

Managing the complexity of designing chips containing billions of transistors requires decoupling computation from communication. For the communication, scalable and compositional interconnects, such as networks on chip (NoC), must be used. It is shown that guaranteed services are essential in achieving this decoupling. Guarantees typically come at the cost of lower resource utilisation. To avoid this, they must be used in combination with best-effort services. The key element of this NoC is a router consisting conceptually of two parts; the so-called guaranteed-throughput (GT) and best-effort (BE) routers. The GT and BE router architectures are combined in an efficient implementation by sharing resources. The trade-offs between hardware complexity and efficiency of the combined router are shown that motivate the choices. The reasoning for the trade-offs is validated with a prototype router implementation. A layout is shown of an input-queued wormhole 5 x 5 router with an aggregate bandwidth of 80 Gbit/s. It occupies 0.26 mm(2) in a 0.13 mum technology. This shows that our router provides high performance at-reasonable cost, bringing NoCs one step closer.