Synthesis of Extremely Large Time-Triggered Network Schedules

Many embedded systems with real-time requirements demand minimal jitter and low communication end-to-end latency for its communication networks. The time-triggered paradigm, adopted by many real-time protocols, was designed to cope with these demands. A cost-efficient way to implement this paradigm is to synthesize a static schedule that indicates the transmission times of all the time-triggered frames such that all requirements are met. Synthesizing this schedule can be seen as a bin-packing problem, known to be NPcomplete, with complexity driven by the number of frames. In the last years, requirements on the amount of data being transmitted and the scalability of the network have increased. A solution was proposed, adapting real-time switched Ethernet to benefit from its high bandwidth. However, it added more complexity in computing the schedule, since every frame is distributed over multiple links. Tools like Satisfiability Modulo Theory solvers were able to cope with the added complexity and synthesize schedules of industrial size networks. Despite the success of such tools, applications are appearing requiring embedded systems with even more complex networks. In the future, real-time embedded systems, such as large factory automation or smart cities, will need extremely large hybrid networks, combining wired and wireless communication, with schedules that cannot be synthesized with current tools in a reasonable amount of time. With this in mind, the first thesis goal is to identify the performance limits of Satisfiability Modulo Theory solvers in schedule synthesis. Given these limitations, the next step is to define and develop a divide and conquer approach for decomposing the entire scheduling problem in smaller and easy solvable subproblems. However, there are constraints that relate frames from different subproblems. These constraints need to be treated differently and taken into account at the start of every subproblem. The third thesis goal is to develop an approach that is able to synthesize schedules when different frame constraints related to different subproblems are inter-dependent. Last, is to define the requirements that the integration of wireless communication in hybrid networks will bring to the schedule synthesis and how to cope with the increased complexity. We demonstrate the viability of our approaches by means of evaluations, showing that our method is capable to synthesize schedules of hundred of thousands of frames in less than 5 hours.RetNe