Formal worst-case timing analysis of Ethernet topologies with strict-priority and AVB switching

Abstract

Ethernet is increasingly recognized as the future communication standard for distributed embedded systems in multiple domains such as industrial automation, automotive and avionics. A main motivation for this is cost and available data rate. A critical issue in the adoption of Ethernet in these domains is the timing of frame transfers, as many relevant applications require a guaranteed low-latency communication in order to meet real-time constraints. Ethernet AVB is an upcoming standard which addresses the timing issues by extending the existing strict-priority arbitration. Still, it needs to be evaluated whether these mechanism suffice for the targeted applications. For safety-critical applications, this can not only be done using intuition or simulation but requires a formal approach to assure the coverage of all worst-case corner cases. Hence, we present in this paper a formal worst-case analysis of the timing properties of Ethernet AVB and strict-priority Ethernet. This analysis mathematically determines safe upper bounds on the latency of frame transfers. Using this approach, we evaluate different topologies for a typical use-case in industrial automation.