Combined task- and network-level scheduling for distributed time-triggered systems

Abstract

Ethernet-based time-triggered networks (e.g. TTEthernet) enable the cost-effective integration of safety-critical and real-time distributed applications in domains where determinism is a key requirement, like the aerospace, automotive, and industrial domains. Time-Triggered communication typically follows an offline and statically configured schedule (the synthesis of which is an NP-complete problem) guaranteeing contention-free frame transmissions. Extending the end-to-end determinism towards the application layers requires that software tasks running on end nodes are scheduled in tight relation to the underlying time-triggered network schedule. In this paper we discuss the simultaneous co-generation of static network and task schedules for distributed systems consisting of preemptive time-triggered tasks which communicate over switched multi-speed time-triggered networks. We formulate the schedule problem using first-order logical constraints and present alternative methods to find a solution, with or without optimization objectives, based on satisfiability modulo theories (SMT) and mixed integer programming (MIP) solvers, respectively. Furthermore, we present an incremental scheduling approach, based on the demand bound test for asynchronous tasks, which significantly improves the scalability of the scheduling problem. We demonstrate the performance of the approach with an extensive evaluation of industrial-sized synthetic configurations using alternative state-of-the-art SMT and MIP solvers and show that, even when using optimization, most of the problems are solved within reasonable time using the incremental method.