A Low-Latency and Flexible TDM NoC for Strong Isolation in Security-Critical Systems

Shared security-critical systems are typically organized as a set of domains that must be kept separate. The network-on-chip (NoC) is key to delivering strong domain isolation, since many of its internal resources are shared between packets from different domains; therefore time-division multiplexing (TDM) is often implemented to avoid any form of interference. Prior approaches to TDM-based scheduling of NoCs lose relevance when they are challenged with conflicting requirements of latency optimization, area efficiency, architectural flexibility and fast reconfigurability. In many cases, aggressive latency optimizations are performed at the cost of timing channel protection. In this paper, we propose a new scheduling approach of time slots in 2D-mesh TDM NoCs that follows directly from the properties of the Channel Dependency Graph. As a result, the isolation-performance trade-off is consistently improved with respect to state-of-the-art solutions across the domain configuration space. When combined with a new token-based mechanism to dispatch scheduling directives, our approach enables the effective reconfiguration of the number of domains, unlike the static nature of most previous proposals.