Minimizing Power Consumption of Spatial Division Based Networks-on-Chip Using Multi-path and Frequency Reduction

With an increasing number of processing elements being integrated on a single die, networks-on-chip (NoCs) are emerging as a significant contributor to overall chip power consumption. While some solutions have been proposed to reduce this power consumption, none of them can be applied to spatial division multiplexing (SDM)-based NoCs. In this paper, we introduce a method to minimize the power consumption of an SDM-based NoC by frequency minimization, while still satisfying the bandwidth requirements. The problem is integrated with the connection-routing problem which is modeled as a mixed-integer quadratic constrained problem (MIQCP). However, solving this MIQCP formulation directly using existing solvers is infeasible for large use-cases. We propose a two-step approach by first computing the minimum feasible frequency for the entire network taking bandwidth of all connections into consideration. This first step reduces the frequency-minimization-routing MIQCP problem into a routing-only mixed-integer linear programming (MILP) problem. In the second step, this MILP problem is solved using a standard ILP solver. Two other techniques are proposed to solve the routing and frequency minimization problem. Experiments are performed with synthetic examples and a case-study with JPEG decoder to evaluate the performance and results of the three methods. MILP-based approach achieves up to 55% power reduction as compared to the other methods albeit at the cost of higher execution time.