Implementing Multi-Periodic Critical Systems: from Design to Code Generation

This article presents a complete scheme for the development of Critical Embedded Systems with Multiple Real-Time Constraints. The system is programmed with a language that extends the synchronous approach with high-level real-time primitives. It enables to assemble in a modular and hierarchical manner several locally mono-periodic synchronous systems into a globally multi-periodic synchronous system. It also allows to specify flow latency constraints. A program is translated into a set of real-time tasks. The generated code (\C\ code) can be executed on a simple real-time platform with a dynamic-priority scheduler (EDF). The compilation process (each algorithm of the process, not the compiler itself) is formally proved correct, meaning that the generated code respects the real-time semantics of the original program (respect of periods, deadlines, release dates and precedences) as well as its functional semantics (respect of variable consumption).Comment: 15 pages, published in Workshop on Formal Methods for Aerospace (FMA'09), part of Formal Methods Week 2009

Ordonnancement hybride des applications flots de données sur des systèmes embarqués multi-coeurs

Les systèmes embarqués sont de plus en plus présents dans l'industrie comme dans la vie quotidienne. Une grande partie de ces systèmes comprend des applications effectuant du traitement intensif des données: elles utilisent de nombreux filtres numériques, où les opérations sur les données sont répétitives et ont un contrôle limité. Les graphes "flots de données", grâce à leur déterminisme fonctionnel inhérent, sont très répandus pour modéliser les systèmes embarqués connus sous le nom de "data-driven". L'ordonnancement statique et périodique des graphes flot de données a été largement étudié, surtout pour deux modèles particuliers: SDF et CSDF. Dans cette thèse, on s'intéresse plus particulièrement à l'ordonnancement périodique des graphes CSDF. Le problème consiste à identifier des séquences périodiques infinies d'actionnement des acteurs qui aboutissent à des exécutions complètes à buffers bornés. L'objectif est de pouvoir aborder ce problème sous des angles différents : maximisation de débit, minimisation de la latence et minimisation de la capacité des buffers. La plupart des travaux existants proposent des solutions pour l'optimisation du débit et négligent le problème d'optimisation de la latence et propose même dans certains cas des ordonnancements qui ont un impact négatif sur elle afin de conserver les propriétés de périodicité. On propose dans cette thèse un ordonnancement hybride, nommé Self-Timed Périodique (STP), qui peut conserver les propriétés d'un ordonnancement périodique et à la fois améliorer considérablement sa performance en terme de latence.One of the most important aspects of parallel computing is its close relation to the underlying hardware and programming models. In this PhD thesis, we take dataflow as the basic model of computation, as it fits the streaming application domain. Cyclo-Static Dataflow (CSDF) is particularly interesting because this variant is one of the most expressive dataflow models while still being analyzable at design time. Describing the system at higher levels of abstraction is not sufficient, e.g. dataflow have no direct means to optimize communication channels generally based on shared buffers. Therefore, we need to link the dataflow MoCs used for performance analysis of the programs, the real time task models used for timing analysis and the low-level model used to derive communication times. This thesis proposes a design flow that meets these challenges, while enabling features such as temporal isolation and taking into account other challenges such as predictability and ease of validation. To this end, we propose a new scheduling policy noted Self-Timed Periodic (STP), which is an execution model combining Self-Timed Scheduling (STS) with periodic scheduling. In STP scheduling, actors are no longer strictly periodic but self-timed assigned to periodic levels: the period of each actor under periodic scheduling is replaced by its worst-case execution time. Then, STP retains some of the performance and flexibility of self-timed schedule, in which execution times of actors need only be estimates, and at the same time makes use of the fact that with a periodic schedule we can derive a tight estimation of the required performance metrics

Cost-Effective Network Planning and Operation for Rural Communities.

PhD Theses.Broadband Internet access is central to the regeneration of remote communities and reducing the digital divide between rural and urban regions. This thesis focuses on rural communities with limited financial resources, environmental issues including long reach from conurbations, and mountainous or otherwise adverse terrain, typically with limited access to a wired power supply. As such, regular access technologies based on cable or fibre optics are not financially viable. To overcome this challenge, we consider the deployment of a Free-Space Optical (FSO) based relay network as the primary technology, using diversity to provide resilience to atmospheric effects. The aim of this research is to design and evaluate a rural network planning and traffic engineering framework employing FSO communication using light emitting diodes/lasers to construct backhaul rural network infrastructures. FSO systems are relatively cheap and easy to implement [1]. Various proof-of-concept technologies already exist [2] [3] [4]. However, the focus of this work is on the design of a flexible network-planning tool together with a robust management framework that is designed to operate over such an infrastructure to ensure it functions efficiently despite changes in load or communication channel outages. Although the work concentrates on an FSO based infrastructure, this could be extended to support heterogeneous networks employing a combination of technologies. More precisely, this research first describes a novel network planning tool with an intelligent resource management system based on a Multi-Objective Evolutionary Algorithm (MOEA) that determines the suitable location of FSO relay nodes, taking into account end-to-end link speed which is bitrate of user data and the degree of path diversity coupling with battery power. This MOEA approach can account for Line-of-Sight occlusions and allows various compromises to be selected from a Pareto front to suit individual needs. We provide suitable results to show the satisfactory operation of the tool and outline avenues for future development. Following on from this, we design and evaluate an intelligent traffic-engineering framework to make the best use of the deployed infrastructure that can adapt to environmental changes. This aims to ensure a good service is maintained at all times by suitable reconfiguration

Compositional Scheduling Analysis Using Standard Event Models

Embedded real-time systems must meet a variety of timing requirements, such as deadlines and limited load or bandwidth. These properties depend heavily on interactions between tasks and on the scheduling of tasks and communications. Unfortunately, the current practice of specialization and re-use results in increasingly heterogeneous systems, which specifically complicates the scheduling analysis problem. Todays best practice of timed simulation is increasingly unreliable, mainly because the corner cases are extremely difficult to find and debug. As an alternative, a variety of systematic and formal approaches to scheduling analysis have been proposed. Most of them, however, are either limited to sub-problems, or use unwieldy and complex models that distract designers in practice. This thesis presents a novel, structured analysis procedure that a) can cope with the increasing complexity and heterogeneity of embedded systems, b) provides the modularity and flexibility that the established, re-use driven system integration style requires, and c) facilitates system integration using a comprehensible analytical model. The approach uses intuitive and standardized event models to represent the interfaces between different components and their scheduling. The clear interface structure allows -for the first time- the modular composition of heterogeneous sub-system analysis techniques. This provides designers with the flexibility to use their preferred scheduling and analysis techniques locally without compromising global scheduling analysis. This new analysis procedure has been implemented in the SymTA/S tool. As it can be efficiently applied in practice, it provides a serious and promising complement to simulation.Eingebettete Echtzeitsysteme müssen eine Vielzahl von Zeit- und Performanzanforderungen erfüllen, z.B. maximale Reaktionszeiten oder vorgegebene Kommunikationsbandbreiten. Die Echtzeiteigenschaften hängen stark vom Zusammenspiel der Einzelkomponenten sowie deren Scheduling ab. Unglücklicherweise führt gerade die in der Praxis etablierte Wiederverwendung von spezialisierten Komponenten zu einer Heterogenität, die die Schedulinganalyse zusätzlich erschwert. Die heute eingesetzten Simulationsverfahren sind zusehends unzuverlässig, da die kritischen Randfälle in der Praxis kaum mehr vollständig bestimmt werden können. Als Alternative wurde eine Vielzahl systematischer und formaler Ansätze vorgeschlagen. Meist sind diese jedoch entweder auf spezielle Teilprobleme beschränkt oder für den Allgemeinfall zu unhandlich und finden daher nur eine geringe Akzeptanz in der industriellen Praxis. In dieser Arbeit wird ein neues Verfahren zur Schedulinganalyse vorgestellt, das a) die steigende Komplexität und Heterogenität angemessen erfasst, b) über die Modularität und Flexibilität verfügt, die mit Wiederverwendung und Integration erforderlich ist, und c) die Integration durch ein nachvollziehbares Analysemodell unterstützt. Das Analysemodell erfasst die komplexen Abhängigkeiten zwischen Komponenten mit Hilfe von intuitiven, standardisierten Ereignismodellen. Die klare Strukturierung dieser Schnittstellen erlaubt erstmals die modulare Komposition von Analysen heterogener Systemteile. Dies gibt Entwicklern die nötige Flexibilität, ihre bevorzugten lokalen Entwurfsmethoden zu benutzen, ohne auf die globale Schedulinganalyse verzichten zu müssen. Das Verfahren bildet die Grundlage für das SymTA/S Analysewerkzeug und ist in der Praxis sehr effizient einsetzbar, womit sich eine ernstzunehmende und viel versprechende Ergänzung zur heute etablierten Performanz-Simulation eröffnet

A Compositional Approach to Embedded System Design

An important observable trend in embedded system design is the growing system complexity. Besides the sheer increase of functionality, the growing complexity has another dimension which is the resulting heterogeneity with respect to the different functions and components of an embedded system. This means that functions from different application domains are tightly coupled in a single embedded system. It is established industry practice that specialized specification languages and design environments are used in each application domain. The resulting heterogeneity of the specification is increased even further by reused components (legacy code, IP). Since there is little hope that a single suitable language will replace this heterogeneous set of languages, multi-language design is becoming increasingly important for complex embedded systems. The key problems in the context of multi-language design are the safe integration of the differently specified subsystems and the optimized implementation of the whole system. Both require the reliable validation of the system function as well as of the non-functional system properties. Current cosimulation-based approaches are well suited for functional validation and debugging. However, these approaches are less powerful for the validation of non-functional system properties. In this dissertation, a novel compositional approach to embedded system design is presented which augments existing cosimulation-based design flows with formal analysis capabilities regarding non-functional system properties such as timing or power consumption. Starting from a truly multi-language specification, the system is transformed into an abstract internal design representation which serves as basis for system-wide analysis and optimization.Ein wesentlicher Trend im Entwurf eingebetteter Systeme ist die steigende Komplexität der zu entwerfenden Systeme. Neben der zunehmenden Funktionalität hat die steigende Komplexität eine weitere Dimension: die resultierende Heterogenität bezüglich der verschiedenen Funktionen und Komponenten eines eingebetteten Systems. Dies bedeutet, daß Funktionen aus verschiedenen Anwendungsbereichen in einem einzelnen System eng miteinander kooperieren. Es ist in der industriellen Praxis etabliert, daß in jedem Anwendungsbereich spezialisierte Spezifikationssprachen zum Einsatz kommen. Da wenig Hoffnung besteht, daß eine einzige geeignete Sprache diesen heterogenen Mix von Sprachen ersetzen wird, gewinnt der mehrsprachige Entwurf für komplexe eingebettete Systeme an Bedeutung. Die Hauptprobleme im Bereich des mehrsprachigen Entwurfs sind die sichere Integration der verschieden spezifizierten Teilsysteme und die optimierte Implementierung des gesamten Systems. Beide Probleme verlangen eine zuverlässige Validierung der Systemfunktion sowie der nichtfunktionalen Systemeigenschaften. Heutige cosimulationsbasierte Ansätze aus Forschung und Industrie sind gut geeignet für die funktionale Validierung und Fehlersuche, haben aber Schwächen bei der Validierung nichtfunktionaler Systemeigenschaften. In der vorliegenden Arbeit wird ein neuartiger kompositionaler Ansatz für den Entwurf eingebetteter Systeme vorgestellt, der existierende cosimulationsbasierte Entwurfsflüsse um Fähigkeiten zur Analyse nichtfunktionaler Systemeigenschaften ergänzt. Ausgehend von einer mehrsprachigen Spezifikation, wird das System in eine abstrakte homogene interne Darstellung transformiert, die als Grundlage für die systemweite Analyse und Optimierung dient