Software Fault Tolerance in Real-Time Systems: Identifying the Future Research Questions

Tolerating hardware faults in modern architectures is becoming a prominent problem due to the miniaturization of the hardware components, their increasing complexity, and the necessity to reduce the costs. Software-Implemented Hardware Fault Tolerance approaches have been developed to improve the system dependability to hardware faults without resorting to custom hardware solutions. However, these come at the expense of making the satisfaction of the timing constraints of the applications/activities harder from a scheduling standpoint. This paper surveys the current state of the art of fault tolerance approaches when used in the context real-time systems, identifying the main challenges and the cross-links between these two topics. We propose a joint scheduling-failure analysis model that highlights the formal interactions among software fault tolerance mechanisms and timing properties. This model allows us to present and discuss many open research questions with the final aim to spur the future research activities

Real-Time Wireless Sensor-Actuator Networks for Cyber-Physical Systems

A cyber-physical system (CPS) employs tight integration of, and coordination between computational, networking, and physical elements. Wireless sensor-actuator networks provide a new communication technology for a broad range of CPS applications such as process control, smart manufacturing, and data center management. Sensing and control in these systems need to meet stringent real-time performance requirements on communication latency in challenging environments. There have been limited results on real-time scheduling theory for wireless sensor-actuator networks. Real-time transmission scheduling and analysis for wireless sensor-actuator networks requires new methodologies to deal with unique characteristics of wireless communication. Furthermore, the performance of a wireless control involves intricate interactions between real-time communication and control. This thesis research tackles these challenges and make a series of contributions to the theory and system for wireless CPS. (1) We establish a new real-time scheduling theory for wireless sensor-actuator networks. (2) We develop a scheduling-control co-design approach for holistic optimization of control performance in a wireless control system. (3) We design and implement a wireless sensor-actuator network for CPS in data center power management. (4) We expand our research to develop scheduling algorithms and analyses for real-time parallel computing to support computation-intensive CPS

Dependable Embedded Systems

This Open Access book introduces readers to many new techniques for enhancing and optimizing reliability in embedded systems, which have emerged particularly within the last five years. This book introduces the most prominent reliability concerns from today’s points of view and roughly recapitulates the progress in the community so far. Unlike other books that focus on a single abstraction level such circuit level or system level alone, the focus of this book is to deal with the different reliability challenges across different levels starting from the physical level all the way to the system level (cross-layer approaches). The book aims at demonstrating how new hardware/software co-design solution can be proposed to ef-fectively mitigate reliability degradation such as transistor aging, processor variation, temperature effects, soft errors, etc. Provides readers with latest insights into novel, cross-layer methods and models with respect to dependability of embedded systems; Describes cross-layer approaches that can leverage reliability through techniques that are pro-actively designed with respect to techniques at other layers; Explains run-time adaptation and concepts/means of self-organization, in order to achieve error resiliency in complex, future many core systems

Adaptive Mid-term and Short-term Scheduling of Mixed-criticality Systems

A mixed-criticality real-time system is a real-time system having multiple tasks classified according to their criticality. Research on mixed-criticality systems started to provide an effective and cost efficient a priori verification process for safety critical systems. The higher the criticality of a task within a system and the more the system should guarantee the required level of service for it. However, such model poses new challenges with respect to scheduling and fault tolerance within real-time systems. Currently, mixed-criticality scheduling protocols severely degrade lower criticality tasks in case of resource shortage to provide the required level of service for the most critical ones. The actual research challenge in this field is to devise robust scheduling protocols to minimise the impact on less critical tasks. This dissertation introduces two approaches, one short-term and the other medium-term, to appropriately allocate computing resources to tasks within mixed-criticality systems both on uniprocessor and multiprocessor systems. The short-term strategy consists of a protocol named Lazy Bailout Protocol (LBP) to schedule mixed-criticality task sets on single core architectures. Scheduling decisions are made about tasks that are active in the ready queue and that have to be dispatched to the CPU. LBP minimises the service degradation for lower criticality tasks by providing to them a background execution during the system idle time. After, I refined LBP with variants that aim to further increase the service level provided for lower criticality tasks. However, this is achieved at an increased cost of either system offline analysis or complexity at runtime. The second approach, named Adaptive Tolerance-based Mixed-criticality Protocol (ATMP), decides at runtime which task has to be allocated to the active cores according to the available resources. ATMP permits to optimise the overall system utility by tuning the system workload in case of shortage of computing capacity at runtime. Unlike the majority of current mixed-criticality approaches, ATMP allows to smoothly degrade also higher criticality tasks to keep allocated lower criticality ones

Schedulability analysis and optimization of time-partitioned distributed real-time systems

RESUMEN: La creciente complejidad de los sistemas de control modernos lleva a muchas empresas a tener que re-dimensionar o re-diseñar sus soluciones para adecuarlas a nuevas funcionalidades y requisitos. Un caso paradigmático de esta situación se ha dado en el sector ferroviario, donde la implementación de las aplicaciones de señalización se ha llevado a cabo empleando técnicas tradicionales que, si bien ahora mismo cumplen con los requisitos básicos, su rendimiento temporal y escalabilidad funcional son sustancialmente mejorables. A partir de las soluciones propuestas en esta tesis, además de contribuir a la validación de sistemas que requieren certificación de seguridad funcional, también se creará la tecnología base de análisis de planificabilidad y optimización de sistemas de tiempo real distribuidos generales y también basados en particionado temporal, que podrá ser aplicada en distintos entornos en los que los sistemas ciberfísicos juegan un rol clave, por ejemplo en aplicaciones de Industria 4.0, en los que pueden presentarse problemas similares en el futuro.ABSTRACT:he increasing complexity of modern control systems leads many companies to have to resize or redesign their solutions to adapt them to new functionalities and requirements. A paradigmatic case of this situation has occurred in the railway sector, where the implementation of signaling applications has been carried out using traditional techniques that, although they currently meet the basic requirements, their time performance and functional scalability can be substantially improved. From the solutions proposed in this thesis, besides contributing to the assessment of systems that require functional safety certification, the base technology for schedulability analysis and optimization of general as well as time-partitioned distributed real-time systems will be derived, which can be applied in different environments where cyber-physical systems play a key role, for example in Industry 4.0 applications, where similar problems may arise in the future

Measurements, Models, Systems and Design

531 s.

A dynamically reconfigurable hard-real-time communication protocol for embedded systems

Echtzeitkommunikation ist eine Grundanforderung für viele verteilte eingebettete Systeme. Für eine neue Klasse von Anwendungen sind jedoch nicht nur Echtzeitfähigkeit, sondern auch Flexibilität und Anpassungsfähigkeit notwendige System-Attribute. Um die Flexibilität zu erhöhen, wurde in dieser Arbeit ein neues Kommunikationsprotokoll namens TrailCable konzipiert. Es profitiert von den Eigenschaften des Earliest Deadline First Scheduling-Verfahrens, wie z. B. der optimalen Ausnutzung von Ressourcen und der Unterstützung von heterogenen Tasks. Ein Kommunikationsnetzwerk wird aufgebaut mit Hilfe von voll-Duplex-, Punkt-zu-Punkt-Verbindungen, wobei die Knoten Datenpakete weiterleiten können, um eine Multi-hop Übertragung zu gewährleisten. Es werden Methoden vorgestellt, die es erlauben, automatisch die Kommunikationsanforderungen erfüllende Echtzeit-Kanäle auf das Netzwerk abzubilden. Echtzeit-Kanäle können nur dann aktiviert werden, wenn im Voraus ein Akzeptanztest erfolgreich durchgeführt wurde. Solch eine Prüfung kann mittels eines Tools automatisch erfolgen. Alle dafür notwendigen Netzwerkinformationen werden aus XML-Dateien eingelesen. Zur Laufzeit prüft ein Mechanismus, der Bandbreitenwächter genannt wird, ob die eingelesenen Pakete mit ihrer Spezifikation übereinstimmen, damit Fehler die Echzeitfähigkeit anderer Kanäle nicht beeinträchtigen können. Zeitkritische Funktionen des Kommunikationsprotokolls, wie Scheduling, Bandbreitenwächter, Routing und Uhrsynchronisation, sind mittels dedizierter Hardware implementiert. Ein voll funktionsfähiger FPGA-basierter Prototyp wurde aufgebaut und in zahlreichen Tests evaluiert, um das Echtzeit-Verhalten des Protokolls unter realen Bedingungen zu testen und zu analysieren.Real-time communication is a basic requirement for many distributed embedded systems. However, for an emerging new class of applications not only real-time behavior but also flexibility and adaptability will become necessary system attributes. In order to increase the flexibility of real-time communication systems a new protocol called TrailCable was designed. It takes advantage of the properties of Earliest Deadline First (EDF) scheduling, which include optimal utilization bounds and the possibility to cope with heterogeneous task sets. A communication network is built with full-duplex, point-to-point links, and nodes can route packets to allow multi-hop message delivery. This work introduces methods for automatically mapping real-time channels on a given network directly from communication requirement specifications. The activation of real-time channels in the network is permitted only after a successful schedulability analysis, which can be executed automatically by a tool that checks XML-based network configuration models. At run-time, the characteristics of all incoming packets are checked against their specification by an admission control technique called bandwidth guardian, which is used to ensure that occasional faults will not impair the timeliness of other real-time channels. Time-critical functions of the communication protocol, such as scheduling, admission control, packet routing, and clock synchronization, are implemented by means of dedicated hardware. A fully operational FPGA-based prototype was built and used in different measurement experiments to validate the real-time behavior of the protocol under real conditions.Tag der Verteidigung: 02.04.2012Paderborn, Univ., Diss., 201

The Sixth Annual Workshop on Space Operations Applications and Research (SOAR 1992)

This document contains papers presented at the Space Operations, Applications, and Research Symposium (SOAR) hosted by the U.S. Air Force (USAF) on 4-6 Aug. 1992 and held at the JSC Gilruth Recreation Center. The symposium was cosponsored by the Air Force Material Command and by NASA/JSC. Key technical areas covered during the symposium were robotic and telepresence, automation and intelligent systems, human factors, life sciences, and space maintenance and servicing. The SOAR differed from most other conferences in that it was concerned with Government-sponsored research and development relevant to aerospace operations. The symposium's proceedings include papers covering various disciplines presented by experts from NASA, the USAF, universities, and industry

Online scheduling for real-time multitasking on reconfigurable hardware devices

Nowadays the ever increasing algorithmic complexity of embedded applications requires the designers to turn towards heterogeneous and highly integrated systems denoted as SoC (System-on-a-Chip). These architectures may embed CPU-based processors, dedicated datapaths as well as recon gurable units. However, embedded SoCs are submitted to stringent requirements in terms of speed, size, cost, power consumption, throughput, etc. Therefore, new computing paradigms are required to ful l the constraints of the applications and the requirements of the architecture. Recon gurable Computing is a promising paradigm that provides probably the best trade-o between these requirements and constraints. Dynamically recon gurable architectures are their key enabling technology. They enable the hardware to adapt to the application at runtime. However, these architectures raise new challenges in SoC design. For example, on one hand, designing a system that takes advantage of dynamic recon guration is still very time consuming because of the lack of design methodologies and tools. On the other hand, scheduling hardware tasks di ers from classical software tasks scheduling on microprocessor or multiprocessors systems, as it bears a further complicated placement problem. This thesis deals with the problem of scheduling online real-time hardware tasks on Dynamically Recon gurable Hardware Devices (DRHWs). The problem is addressed from two angles : (i) Investigating novel algorithms for online real-time scheduling/placement on DRHWs. (ii) Scheduling/Placement algorithms library for RTOS-driven Design Space Exploration (DSE). Regarding the first point, the thesis proposes two main runtime-aware scheduling and placement techniques and assesses their suitability for online real-time scenarios. The first technique discusses the impact of synthesizing, at design time, several shapes and/or sizes per hardware task (denoted as multi-shape task), in order to ease the online scheduling process. The second technique combines a looking-ahead scheduling approach with a slots-based recon gurable areas management that relies on a 1D placement. The results show that in both techniques, the scheduling and placement quality is improved without signi cantly increasing the algorithm time complexity. Regarding the second point, in the process of designing SoCs embedding recon gurable parts, new design paradigms tend to explore and validate as early as possible, at system level, the architectural design space. Therefore, the RTOS (Real-Time Operating System) services that manage the recon gurable parts of the SoC can be re fined. In such a context, gathering numerous hardware tasks scheduling and placement algorithms of various complexity vs performance trade-o s in a kind of library is required. In this thesis, proposed algorithms in addition to some existing ones are purposely implemented in C++ language, in order to insure the compatibility with any C++/SystemC based SoC design methodology.EThOS - Electronic Theses Online ServiceGBUnited Kingdo