Affine-NoC: multi-ring NoCs exploiting long physical links

Abstract

Routerless multi-ring proposals are low-cost NoCs that employ multiple independent rings, avoiding any crossbars or arbitration mechanisms. Their complexity lies on the selection of the set of rings to connect all the nodes. Previous proposals result in unbalanced designs with high hop counts. This work introduces Affine-NoC, a balanced routerless NoC based on a novel arrangement of rings derived from the Affine Plane. Affine-NoC exploits express channels to connect distant processing elements, allowing for a completely balanced layout of the set of rings and a reduction in average distance and diameter without sacrificing bisection bandwidth. Analysis shows that Affine-NoC presents a balanced design with a low number of rings per node and reduced complexity, similar cost to previous proposals in terms of aggregated link length, while it simplifies the multiplex units and reduces the hop count. Simulation results show that Affine-NoC reduces hop count and average latency by 76% and 20.5% respectively compared to previous designs, it reduces deflections by 27% and avoids unfairness, making it a feasible alternative for multi-ring routerless NoCs.