Reduced worst-case communication latency using single-cycle multi-hop traversal network-on-chip

Abstract

The communication latency in traditional Network-on-Chip (NoC) with hop-by-hop traversal is inherently restricted by the distance between source-destination communicating pairs. SMART, as one of the dynamically reconfigurable NoC architectures, enables the new feature of single-cycle long-distance communication by building a direct bypass path between distant cores dynamically at runtime. With the increasing of the number of integrated cores in multi/many-core systems, SMART has been deemed a promising communication backbone in such systems. However, SMART is generally optimized for average-case performance for best-effort traffics, not offering real-time guaranteed services for real-time traffics, and thus SMART often shows extremely poor real-time performance (e.g. schedulability). To make SMART latency-predictable for real-time traffics, by combining with the single-cycle bypass forwarding technique, in this paper, we firstly propose a priority-preemptive scheduling to allow contending packets to be arbitrated according to predefined priorities. Based on the priority-based scheduling, for the real-time packet flows with given flow mapping and predefined priorities, we then propose a real-time communication analysis model, by considering shared virtual channels (or priority levels) and arbitrary-deadline real-time packet flows, to predict the worst-case communication latency and validate the schedulability. Through theoretical and experimental comparison, the worst-case communication latency of the analyzed packet flows is reduced significantly compared with that of the traditional priority-preemptive NoCs with hop-by-hop traversal and the original distance-based SMART, thus improving the schedulability.