Useful-state encoding: Network control with minimal redundancy

This paper presents useful-state encoding (USE), a novel method to design control circuitry for networks featuring global topological scheduling. These include low-power on-chip networks, for which USE was originally developed. To use it, we first establish a minimal state-space description by specifying the demands on a communication architecture in an optimal way. This useful state-space is much smaller than the full combinatorial state-space of the network. The goal of USE is then a small control circuit, consuming little area and power. We propose analysis and design methods for the control circuit, deduce rules of thumb from use cases, and reach a conclusion on the scalability of our design method with large networks. We find that control circuits remain feasible as long as the number of network nodes remains reasonably low. Feasibility is determined mainly by issues of algorithmic and methodological complexity, not by physical on-chip limitations like area, latency or power.