Development of software for embedded real-time systems poses severalchallenges. Hard and soft constraints on timing, and usually considerableresource limitations, put important constraints on the development. Thetraditional way of coping with these issues is to produce a fully static design,i.e. one that is fully fixed already during design time.Current trends in the area of embedded systems, including the emergingopenness in these types of systems, are providing new challenges for theirdesigners – e.g. integration of new software during runtime, software upgradeor run-time adaptation of application behavior to facilitate better performancecombined with more ecient resource usage. One way to reach these goals is tobuild self-configurable systems, i.e. systems that can resolve such issues withouthuman intervention. Such mechanisms may be used to promote increasedsystem openness.This thesis covers some of the challenges involved in that development.An overview of the current situation is given, with a extensive review ofdi erent concepts that are applicable to the problem, including adaptivitymechanisms (incluing QoS and load balancing), middleware and relevantdesign approaches (component-based, model-based and architectural design).A middleware is a software layer that can be used in distributed systems,with the purpose of abstracting away distribution, and possibly other aspects,for the application developers. The DySCAS project had as a major goaldevelopment of middleware for self-configurable systems in the automotivesector. Such development is complicated by the special requirements thatapply to these platforms.Work on the implementation of an adaptive middleware, DyLite, providingself-configurability to small-scale microcontrollers, is described andcovered in detail. DyLite is a partial implementation of the concepts developedin DySCAS.Another area given significant focus is formal modeling of QoS andresource management. Currently, applications in these types of systems arenot given a fully formal definition, at least not one also covering real-timeaspects. Using formal modeling would extend the possibilities for verificationof not only system functionality, but also of resource usage, timing and otherextra-functional requirements. This thesis includes a proposal of a formalismto be used for these purposes.Several challenges in providing methodology and tools that are usablein a production development still remain. Several key issues in this areaare described, e.g. version/configuration management, access control, andintegration between di erent tools, together with proposals for future workin the other areas covered by the thesis. / Utveckling av mjukvara för inbyggda realtidssystem innebär flera utmaningar.Hårda och mjuka tidskrav, och vanligtvis betydande resursbegränsningar,innebär viktiga inskränkningar på utvecklingen. Det traditionellasättet att hantera dessa utmaningar är att skapa en helt statisk design, d.v.s.en som är helt fix efter utvecklingsskedet.Dagens trender i området inbyggda system, inräknat trenden mot systemöppenhet,skapar nya utmaningar för systemens konstruktörer – exempelvisintegration av ny mjukvara under körskedet, uppgradering av mjukvaraeller anpassning av applikationsbeteende under körskedet för att nå bättreprestanda kombinerat med e ektivare resursutnyttjande. Ett sätt att nå dessamål är att bygga självkonfigurerande system, d.v.s. system som kan lösa sådanautmaningar utan mänsklig inblandning. Sådana mekanismer kan användas föratt öka systemens öppenhet.Denna avhandling täcker några av utmaningarna i denna utveckling. Enöversikt av den nuvarande situationen ges, med en omfattande genomgångav olika koncept som är relevanta för problemet, inklusive anpassningsmekanismer(inklusive QoS och lastbalansering), mellanprogramvara och relevantadesignansatser (komponentbaserad, modellbaserad och arkitekturell design).En mellanprogramvara är ett mjukvarulager som kan användas i distribueradesystem, med syfte att abstrahera bort fördelning av en applikation överett nätverk, och möjligtvis även andra aspekter, för applikationsutvecklarna.DySCAS-projektet hade utveckling av mellanprogramvara för självkonfigurerbarasystem i bilbranschen som ett huvudmål. Sådan utveckling försvåras avde särskilda krav som ställs på dessa plattformarArbete på implementeringen av en adaptiv mellanprogramvara, DyLite,som tillhandahåller självkonfigurerbarhet till småskaliga mikrokontroller,beskrivs och täcks i detalj. DyLite är en delvis implementering av konceptensom utvecklats i DySCAS.Ett annat område som får särskild fokus är formell modellering av QoSoch resurshantering. Idag beskrivs applikationer i dessa områden inte heltformellt, i varje fall inte i den mån att realtidsaspekter täcks in. Att användaformell modellering skulle utöka möjligheterna för verifiering av inte barasystemfunktionalitet, men även resursutnyttjande, tidsaspekter och andraicke-funktionella krav. Denna avhandling innehåller ett förslag på en formalismsom kan användas för dessa syften.Det återstår många utmaningar innan metodik och verktyg som är användbarai en produktionsmiljö kan erbjudas. Många nyckelproblem i områdetbeskrivs, t.ex. versions- och konfigurationshantering, åtkomststyrning ochintegration av olika verktyg, tillsammans med förslag på framtida arbete iövriga områden som täcks av avhandlingen. / DySCAS

Dans cette thèse, nous nous intéressons à la problématique de la vérification formelle des systèmes critiques temps réel, c’est-à-dire des systèmes dont l’exécution dépend de certaines contraintes temporelles. La spécification formelle des exigences pour de tels systèmes, ainsi que leur vérification, reste une tâche très compliquée, surtout pour les non experts. Plusieurs solutions ont été proposées pour faciliter la spécification et la vérification des systèmes temps-réels. Un premier type d’approche est basée sur la définition d’un ensemble de patrons de spécification qui représentent les propriétés les plus utilisées en pratique. Cependant, ce type de solutions n’est pas toujours supporté par un outillage de vérification efficace, dans le sens que les auteurs de ces langages de patrons ne fournissent pas directement une implantation pour leur langage. Un second type d’approches repose sur l’utilisation du formalisme des logiques temporelles pour spécifier les propriétés à vérifier et sur les techniques de model-checking pour leur vérification. S’agissant de systèmes temps-réels, il est dans ce cas nécessaire d’utiliser des extensions temporisées des logiques temporelles. Cependant, ces approches donnent le plus souvent lieu à des problèmes de model-checking qui sont indécidable, ou dont la complexité en pratique est très élevée. Dans ce travail, nous suivons la première approche et proposons un langage de patrons de propriétés temps-réels accompagnés d’un outil de vérification par model- checking. Nous apportons plusieurs contributions à ce domaine. Nous proposons un cadre théorique complet pour la spécification et la vérification de patrons de propriétés temps réel. Notre approche a été implantée dans le contexte du langage de modélisation Fiacre. Enfin, nous définissons deux méthodes complémentaires permettant de vérifier la correction de notre approche de vérification / The formal verification of critical, reactive systems is a very complicated task, especially for non experts. In this work, we more particularly address the problem of real time systems, that is in the situation where the correctness of the system depends upon timing constraints, such as the “timeliness” of some interactions. Many solutions have been proposed to ease the specification and the verification of such systems. An interesting approach—that we follow in this thesis—is based on the definition of specification patterns, that is sets of general, reusable templates for commonly occurring classes of properties. However, patterns are rarely implemented, in the sense that the designers of specification languages rarely provide an effective verification method for checking a pattern on a system. The most common technique is to rely on a timed extension of a temporal logic to define the semantics of patterns and then to use a model-checker for this logic. However, this approach may be inadequate, in particular if patterns require the use of a logic associated to an undecidable model-checking problem or to an algorithm with a very high practical complexity. We make several contributions. We propose a complete theoretical framework to specify and check real time properties on the formal model of a system. First, our framework provides a set of real time specification patterns. We provide a verification technique based on the use of observers that has been implemented in a tool for the Fiacre modelling language. Finally, we provide two methods to check the correctness of our verification approach; a “semantics”—theoretical— method as well as a “graphical”-practical- method

Modern general purpose programming languages like Java or C# provide a rich feature set and a higher degree of abstraction than conventional real-time programming languages like C/C++ or Ada. Applications developed with these modern languages are typically deployed via platform independent intermediate code. The intermediate code is typically executed by a virtualizing runtime environment. This allows for a high portability. Prominent examples are the Dalvik Virtual Machine of the Android operating system, the Java Virtual Machine as well as Microsoft .NET’s Common Language Runtime. The virtualizing runtime environment executes the instructions of the intermediate code. This introduces additional challenges to real-time software development. One issue is the transformation of the intermediate code instructions to native code instructions. If this transformation interferes with the execution of the real-time application, this might introduce jitter to its execution times. This can degrade the quality of soft real-time systems like augmented reality applications on mobile devices, but can lead to severe problems in hard real-time applications that have strict timing requirements. This thesis examines the possibility to overcome timing issues with intermediate code execution in virtualizing runtime environments. It addresses real-time suitable generation of native code from intermediate code in particular. In order to preserve the advantages of modern programming languages over conventional ones, the solution has to adhere to the following main requirements: - Intermediate code transformation does not interfere with application execution - Portability is not reduced and code transformation is still transparent to a programmer - Comparable performance Existing approaches are evaluated. A concept for real-time suitable code generation is developed. The concept bases on a pre-allocation of the native code and the elimination of indirect references, while considering and optimizing startup time of an application. This concept is implemented by the extension of an existing virtualizing runtime environment, which does not target real-time systems per se. It is evaluated qualitatively and quantitatively. A comparison of the new concept to existing approaches reveals high execution time determinism and good performance and while preserving the portability deployment of applications via intermediate code.

Real-time systems surround every facet of our lives. They can be found in anything from everyday objects like mobile phones and washing machines to objects critical to life and infrastructure including heart rate monitors and nuclear power plants. As time progresses these systems are becoming ever more complex. To cope with the increase in complexity, developers and researchers are turning to model driven development as a solution. One modeling language aimed specifically at real-time systems is UML-RT. This thesis proposes an algorithm that for a significant subset of UML-RT is able to provide a worst-case execution time analysis for capsules at a model level. Having access to the worst-case execution times allows developers to at an early stage reason about a given system. This allows for better resource allocation as well as the ability to perform scheduling analysis. Development of the algorithm was performed iteratively using the constructive research approach. We began by first gaining an understanding of the theory. We then successively developed a theoretical algorithm selecting one or a few UML-RT entities at a time. With each iteration the algorithm was redefined to incorporate the new entities. At the end of the development, we created an implementation of the algorithm as an Eclipse Modeling Framework plug-in using Java. We then created a set of hard coded capsule models which were used to validate the algorithm.

Biomedical applications offer an exciting growth opportunity for wireless sensor networks. However, radio frequency communication is problematic in hospital environments that are susceptible to interference in the industrial, scientific, and medical (ISM) bands. Also, RF is inherently insecure as eavesdroppers can easily pick up signals. The Intra-Body Network (IBNet) proposes a novel communication model for biomedical sensor networks. It seeks the convenience of wireless communication while avoiding interference and privacy concerns associated with RF. IBNet's solution is to utilize a subject's own body tissue as a transmission medium. Assuming that transmissions are contained within the body, IBNet solves otherwise complex problems of privacy and interference. Unfortunately, transmitting through the same medium in which we sense creates a new type of conflict; it is possible that one sensor's network transmission might corrupt an adjacent sensor's sample data. We present Body Language, a set of protocols that arbitrate IBNet's sampling/communication conflict while providing basic services such as dynamic node discovery, network configuration, quality of service, and sensor sample collection. Body Language seeks to provide these services and solve IBNet's unique communication challenges while minimizing hardware resource requirements and hence sensor node cost. In order to prove Body Language feasibility, we created an IBNet prototype environment where the protocols were demonstrated on real hardware and in real time. The prototype also offers important insight into the Body Language's computational resource requirements. Our results show that Body Language provides all services required by IBNet and it does so with a very modest footprint.

Increasing complexity of real-time systems and demands for enabling their configurability and tailorability are strong motivations for applying new software engineering principles such as aspect-oriented and component-based software development. The integration of these two techniques into real-time systems development would enable: (i) efficient system configuration from the components in the component library based on the system requirements, (ii) easy tailoring of components and/or a system for a specific application by changing the behavior (code) of the component by aspect weaving, and (iii) enhanced flexibility of the real-time and embedded software through the notion of system configurability and component tailorability. In this thesis we focus on applying aspect-oriented and component-based software development to real-time system development. We propose a novel concept of aspectual component-based real-time system development (ACCORD). ACCORD introduces the following into real-time system development: (i) a design method that assumes the decomposition of the real-time system into a set of components and a set of aspects, (ii) a real-time component model denoted RTCOM that supports aspect weaving while enforcing information hiding, (iii) a method and a tool for performing worst-case execution time analysis of different configurations of aspects and components, and (iv) a new approach to modelling of real-time policies as aspects. We present a case study of the development of a configurable real-time database system, called COMET, using ACCORD principles. In the COMET example we show that applying ACCORD does have an impact on the real-time system development in providing efficient configuration of the real-time system. Thus, it could be a way for improved reusability and flexibility of real-time software, and modularization of crosscutting concerns. In connection with development of ACCORD, we identify criteria that a design method for component-based real-time systems needs to address. The criteria include a well-defined component model for real-time systems, aspect separation, support for system configuration, and analysis of the composed real-time system. Using the identified set of criteria we provide an evaluation of ACCORD. In comparison with other approaches, ACCORD provides a distinct classification of crosscutting concerns in the real-time domain into different types of aspects, and provides a real-time component model that supports weaving of aspects into the code of a component, as well as a tool for temporal analysis of the weaved system. / <p>Report code: LiU-TEK-LIC-2003:23.</p>

During the past decades of research in Real-Time systems, non-preemptive scheduling and fully preemptive scheduling have been extensively investigated, as well as compared with each other. However, it has been shown that none of the two scheduling paradigms dominates over the other in terms of schedulability. In this context, Limited Preemptive Scheduling (LPS) has emerged as an attractive alternative with respect to, e.g., increasing the overall system schedu- lability, efficiently reducing the blocking by lower priority tasks (compared to non-preemptive scheduling) as well as efficiently controlling the number of preemptions, thus controlling the overall preemption-related delay (compared to fully-preemptive scheduling). Several approaches within LPS enable the above mentioned advantages. In our work, we consider the Fixed Preemption Point Scheduling (LP-FPP) as it has been proved to effectively reduce the preemption-related delay compared to other LPS approaches. In particular, LP-FPP facilitates more precise estimation of the preemption-related delays, since the preemption points of a task in LP-FPP are explicitly selected during the design phase, unlike the other LPS approaches where the preemption points are determined at runtime. The main goal of the proposed work is to improve the schedulability of real-time systems under the LP-FPP approach. We investigate its use in different domains, such as: single core hard real-time systems, partitioned multi-core systems and real-time systems which can occasionally tolerate deadline misses. We enrich the state of the art for the single core hard real-time systems by proposing a novel cache-related preemption delay analysis, towards reducing the pessimism of the previously proposed methods. In the context of partitioned multi-core scheduling we propose a novel partitioning criterion for the Worst-Fit Decreasing based partitioning, and we also contribute with the comparison of existing partitioning strategies for LP-FPP scheduling. Finally, in the context of real-time systems which can occasionally tolerate deadline misses, we contribute with a probabilistic response time analysis for LP-FPP scheduling and a preemption point selection method for reducing the deadline-misses of the tasks.

Radio spectrum has become increasingly scarce due to the proliferation of new wireless communication services. This problem has been exacerbated by fixed bandwidth licensing policies that often lead to spectral underutilization. Cognitive radio networks (CRN) can address this issue using flexible spectrum management that permits unlicensed (secondary) users to access the licensed spectrum. Supporting real-time quality-of-service (QoS) in CRNs however, is very challenging, due to the random spectrum availability induced by the licensed (primary) user activity. This thesis considers the problem of real-time voice transmission in CRNs with an emphasis on secondary network ``friendliness''. Friendliness is measured by the secondary real-time voice capacity, defined as the number of connections that can be supported, subject to typical QoS constraints. The constant bit rate (CBR) air interface case is first assumed. An offline scheduler that maximizes friendliness is derived using an integer linear program (ILP) that can be solved using a minimum cost flow graph construction. Two online primary scheduling algorithms are then introduced. The first algorithm is based on shaping the primary spectral hole patterns subject to primary QoS constraints. The second applies real-time scheduling to both primary traffic and virtual secondary calls. The online scheduling algorithms are found to perform well compared to the friendliness upper bound. Extensive simulations of the primary friendly schedulers show the achievable secondary voice capacity for a variety of parameters compared to non-friendly primary scheduling. The thesis then considers the variable bit rate (VBR) air interface option for primary transmissions. Offline and online approaches are taken to generate a primary VBR traffic schedule that is friendly to secondary voice calls. The online VBR schedulers are found to perform well compared to the friendliness upper bound. Simulation results are presented that show the effect of the primary traffic load and primary network delay tolerance on the primary network friendliness level towards potential secondary voice traffic. Finally, secondary user friendliness is considered from an infrastructure deployment point of view. A cooperative framework is proposed, which allows the primary traffic to be relayed by helper nodes using decode-and-forward (DF) relaying. This approach decreases the primary traffic channel utilization, which, in turn, increases the capacity available to potential secondary users. A relay selection optimization problem is first formulated that minimizes the primary channel utilization. A greedy algorithm that assigns relay nodes to primary data flows is introduced and found to perform well compared to the optimum bound. Results are presented that show the primary network friendliness for different levels of primary channel utilization. / Dissertation / Doctor of Philosophy (PhD)

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