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Martinez Garcia, Jorge Luis, (2021)  - Analisi di schedulabilitą real-time per sistemi embedded per automotive  - , Tesi di dottorato - (, , Universitą degli studi di Modena e Reggio Emilia ) - pagg. -

Abstract: Modern automotive embedded systems are composed of multiple real-time tasks communicating by means of shared variables. The effect of an initial event is typically propagated to an actuation signal through sequences of tasks writing/reading shared variables, creating an effect chain. The responsiveness, performance and stability of the control algorithms of an automotive application typically depend on the propagation delays of selected effect chains. Depending on the communication model adopted, the propagation delay of an effect chain may significantly vary, as may be the resulting overhead and memory footprint. In this work, the trade-offs between three communication models that are widely adopted for industrial automotive systems, namely Explicit, Implicit, and Logical Execution Time (LET), are explored. In particular, a formal analysis of the LET model is provided for real-time systems composed of periodic tasks with harmonic and non-harmonic periods, analytically characterizing the control performance of LET effect chains. It is shown that by introducing tasks offsets, the real-time performance of non-harmonic tasks may improve, getting closer to the constant end-to-end latency experienced in the harmonic case. Further, a heuristic algorithm is introduced that obtains a set of offsets that might reduce end-to-end latencies, improving LET communication determinism. The results are compared against an industrial case study consisting of an automotive engine control system. On the other hand, real-time servers have been widely explored in the scheduling literature to predictably execute aperiodic activities, as well as to allow hierarchical scheduling settings. As they facilitate timing isolation between different software components, there is a renewed interest for the adoption of fixed priority real-time servers in the automotive domain, as a way to implement more efficient reservation mechanisms than TDMA-based methods. In this thesis, the extended Polling Periodic, the Deferrable and Sporadic Servers are the main focus. Despite their popularity, only sufficient schedulability conditions exist for real-time systems scheduled with any of these servers. Thus, a formal characterization of an exact response time analysis for fixed priority systems based on the aforementioned servers in a multi-level scheduling setting under preemptive scheduling is developed. In addition to that, an experimental characterization of the schedulabilty improvement that can be obtained with respect to existing sufficient schedulability tests is provided, proving the effectiveness of the proposed exact analysis. Additionally, an overhead-aware schedulability analysis for hierarchical fixed priority preemptive systems is given, and a practical server parameterization heuristic technique, that preserves the least possible utilization as well as enhances the aggregated WCRT of the tasks in a hierarchical scheduling setting, is exposed. Moreover, the temporal isolation offered by the above-mentioned servers is further exploit to serve tasks originally scheduled in the background so that they can meet their deadlines. Hence, a method to implement a Deferrable Server (DS) on top of ETAS RTA-OS, a ubiquitous AUTOSAR-compliant OS, is presented and a heuristic to select its parameters is proposed. Lastly, the effectiveness of the parametrization is proven by applying the technique to an industrial case study consisting of an automotive engine control system.