Routing Table Minimization for Irregular Mesh NoCs

Abstract

The majority of current Network on Chip (NoC) architectures employ mesh topology and use simple static routing, to reduce power and area. However, regular mesh topology is unrealistic due to variations in module sizes and shapes, and is not suitable for application-specific NoCs. Consequently, simplistic routing techniques such as XY routing are inadequate, raising the need for low cost alternatives which can work in irregular mesh networks. In this paper we present a novel technique for reducing the total hardware cost of routing tables for both source and distributed routing approaches. The proposed technique is based on applying a fixed routing function combined with minimal deviation tables that are used only when the routing decisions for a given destination deviate from the predefined routing function. We apply this methodology to compare three hardware efficient routing methods for irregular mesh topology NoCs. For each method, we develop path selection algorithms that minimize the overall cost of routing tables. Finally, we demonstrate by simulations on random and specific real application network instances a significant cost saving compared to standard solutions, and examine the scaling of cost savings with growing NoC size.1