<p>Real-time systems are required to answer to external stimuli within a specified time-period. For this to be possible, the systems behaviour must be predictable. The use of active databases in real-time systems introduces unpredictability in the system, e.g. due to their use of active rules. The behaviour in active databases is usually specified in ECA-rules. Sets of ECA-rules are hard to analyse, which implies that the behaviour of the ECA-rule set is hard to predict.</p><p>The purpose of this project is to evaluate the ability to support the development of a predictable ECA-rule set. Using a formal method for the specification task is desirable, since a formal specification is analysable and can be proven correct. In this project, timed-automata are used for specifying the systems behaviour. A method for deriving predictable ECA-rules from a timed-automaton specification is developed, and successfully applied on a case-study specification. For this case-study specification, a set of ECA-rules preserving the analysed behaviour of the timed-automata specification is derived.</p>

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Timed automata are a formalism to model, verify, and synthesize real-time systems. They have the advantage of having an abstract mathematical semantics, which allow formalizing and solving several verification and synthesis problems. However, timed automata are intended to design models, rather than completely describe real systems. Therefore, once the design phase is over, it remains to check whether the behavior of an actual implementation corresponds to that of the timed automaton model. An important step before implementing a system design is ensuring its robustness. This thesis considers a notion of robustness that asks whether the behavior of a given timed automaton is preserved, or can be made so, when it is subject to small perturbations. Several approaches are considered: Robustness analysis seeks to decide whether a given timed automaton tolerates perturbations, and in that case to compute the (maximum) amount of tolerated perturbations. In robust synthesis, a given system needs to be controlled by a law (or strategy) which tolerates perturbations upto some computable amount. In robust implementation, one seeks to automatically transform a given timed automaton model so that it tolerates perturbations by construction. Several perturbation models are considered, ranging from introducing error in time measures (guard enlargement), forbidding behaviors that are too close to boundaries (guard shrinking), and restricting the time domain to a discrete sampling. We also formalize robust synthesis problems as games, where the control law plays against the environment which can systematically perturb the chosen moves, by some bounded amount. These problems are studied on timed automata and their variants, namely, timed games, and weighted timed automata and games. Algorithms for the parameterized robustness analysis against guard enlargements, and guard shrinkings are presented. The robust synthesis problem is studied for two variants of the game semantics, for timed automata, games, and their weighted extensions. A software tool for robustness analysis against guard shrinkings is presented, and experimental results are discussed. The robust implementation problem is also studied in two different settings. In all algorithms, an upper bound on perturbations that the given timed automaton tolerates can be computed.

Complexity and variety of systems that are working in real time mode need to be specified regarding all behavior conditions. The correctness of the specification, determines whether implemented system will supply conditions that were set. To ensure that specification of the described real-time system is correct, we have to do verification and validation of the specification. Traditional verification methods do not assure full real time system inspection. The main drawback, talking about them, is impossibility of system evaluation according time. In this paper a reachable states graph and its generating algorithms are described, while two time moments are compared using linear programming, Simplex method. Therefore, method for checking equivalent state in system behavioral pathway was suggested. Also, theoretical reasoning for creating computer applications, which automates generation of reachable states graph, is given. Reachable states graph fully evaluates real time system behavior.

The aim of this research is to create the modeling and simulation tool for the real time systems. The component based object oriented model of real time system is introduced as solution. This model uses JAVA and XML languages to specify one component of the real time system. The model can be used to generate source code directly from components specifications. The modeling and simulation system was created based on component model. It can be used for modeling real time systems of any domain, any abstraction level or any complexity level. The experiments show that proposed modeling technique is correct.

A real-time system is one in which the correctness of the computations not only depends upon the logical correctness of the computation but also upon the time at which the result is produced. If the timing constraints of the system are not met, system failure is said to have occurred. Real-time system consist specialized hardware an software components. Nowadays, systems are so big and complex that teams of architects, analysts, programmers, testers and users must work together to create reliable real-time system. To manage this, a number of system development life cycle models have been created. System development life cycle refers to a methodology for developing systems. It provides a consistent framework of tasks and deliverables needed to develop systems. System development consist stages, that are common for all models: project planning, requirements definition, system design, implementation, testing, deployment and maintenance. However, there still are problems, that lead project to the failure. Problems appear while iterating from design stage to the implementation or prototype creation. Thesis describes methodology, that provide a way to overcome these problems. The main idea is to transform functional structure of the real-time system, that is designed using easy to understand graphical environment, to the executable code that will be able to run on target hardware components. Thesis describe the methods of doing such transformation. Methodology allows to create... [to full text]

Gausybė sudėtingų realaus laiko sistemų turi būti specifikuotos įvertinant visas galimas situacijas. Specifikacijos teisingumas reiškia, kad sistema užduotomis sąlygomis pasieks norimą rezultatą. Norėdami užtikrinti, kad aprašyta specifikacija yra teisinga, reikia atlikti sistemos verifikavimą ir validavimą. Tradiciniai verifikavimo metodai neužtikrina pilno sistemos patikrinimo. Pagrindinis jų trūkumas yra tai, kad jos negali įvertinti laikinių charakteristikų. Per keletą paskutinių metų, buvo sukurti nauji metodai, kuriuose įvykių įvykimo laikas priklauso intervalams. Šiame darbe šie metodai buvo patobulinti, kad pilnai aprašytų realaus laiko sistemų veiksenas. Šiame darbe pateikiamas pasiekiamų būsenų medžio sudarymo algoritmas, kai sistemos pabaigos laikų momentų aibė priklauso bet kokiam intervalui - griežtam, negriežtam, griežtam iš kairės arba dešinės. / Complexity and variety of systems that are working in real time mode need to be specified regarding all behavior conditions. The correctness of the specification, determines whether implemented system will supply conditions that were set. To ensure that specification of the described real-time system is correct, we have to do verification and validation of the specification. Traditional verification methods do not assure full real time system inspection. The main drawback, talking about them, is impossibility of system evaluation according time. In past few years, new methods were implemented, whereat real time system events befall in time interval. In this paper, these methods were improved to fully specify real time systems behaviour. Reachable states graph and its generating algorithms are described here, wherein real time system events befall in any type of time interval – inclusive, exclusive in left, right or both sides.

Scheduling of aperiodic and independent tasks in hard real-time symmetric multiprocessing systems is an NP-complete problem that is often solved using heuristics like particle swarm optimization (PSO). The performance of these class of heuristics, known as evolutionary algorithms, are often evaluated based on the number of iterations it takes to find a solution. Such metrics provide limited information on how the algorithm reaches a solution and how the process could be accelerated. This thesis presents a methodology to analyze the trajectory formed by candidate solutions in order to analyze them in both the time and frequency domains at a single scale. The analysis entails (i) the impact of different parameters for the PSO algorithm, and (ii) the evolutionary processes in the swarm. The work reveals that particles have a directed movement towards a solution during a transient phase, and then enter a steady state where they perform an unguided local search. The scheduling algorithm presented in this thesis uses a variation of the minimum total tardiness with cumulative penalties cost function, that can be extended to suit different system needs. The experimental results show that the scheduler is able to distribute tasks to meet the real-time deadlines over 1, 2, and 4 processors and up to 30 tasks with overall system loads of up to 50\% in fewer than 1,000 iterations. When scheduling greater loads, the scheduler reaches local solutions with 1 to 2 missed deadlines, while larger tasks sets take longer to converge. The trajectories of the particles during the scheduling algorithm are examined as a means to emphasize the impact of the behaviour on the application performance and give insight into ways to improve the algorithm for both space and terrestrial applications.

Ubiquitous deployment of embedded systems is having a substantial impact on our society, since they interact with our lives in many critical real-time applications. Typically, embedded systems used in safety or mission critical applications (e.g., aerospace, avionics, automotive or nuclear domains) work in harsh environments where they are exposed to frequent transient faults such as power supply jitter, network noise and radiation. They are also susceptible to errors originating from design and production faults. Hence, they have the design objective to maintain the properties of timeliness and functional correctness even under error occurrences. Fault-tolerance plays a crucial role towards achieving dependability, and the fundamental requirement for the design of effective and efficient fault-tolerance mechanisms is a realistic and applicable model of potential faults and their manifestations. An important factor to be considered in this context is the random nature of faults and errors, which, if addressed in the timing analysis by assuming a rigid worst-case occurrence scenario, may lead to inaccurate results. It is also important that the power, weight, space and cost constraints of embedded systems are addressed by efficiently using the available resources for fault-tolerance. This thesis presents a framework for designing predictably dependable embedded real-time systems by jointly addressing the timeliness and the reliability properties. It proposes a spectrum of fault-tolerance strategies particularly targeting embedded real-time systems. Efficient resource usage is attained by considering the diverse criticality levels of the systems' building blocks. The fault-tolerance strategies are complemented with the proposed probabilistic schedulability analysis techniques, which are based on a comprehensive stochastic fault and error model.

Nowadays, different companies use Ethernet for different industrial applications. Industrial Ethernet has some specific requirements due to its specific applications and environmental conditions which is the reason that makes it different than corporate LANs. Real-time guarantees, which require precise synchronization between all communication devices, as well as reliability are the keys in performance evaluation of different methods [1].  High bandwidth, high availability, reduced cost, support for open infrastructure as well as deterministic architecture make packet-switched networks suitable for a variety of different industrial distributed hard real-time applications. Although research on guaranteeing timing requirements in packet-switched networks has been done, communication reliability is still an open problem for hard real-time applications. In this thesis report, a framework for enhancing the reliability in multihop packet-switched networks is presented. Moreover, a novel admission control mechanism using a real-time analysis is suggested to provide deadline guarantees for hard real-time traffic. A generic and flexible simulator has been implemented for the purpose of this research study to measure different defined performance metrics. This simulator can also be used for future research due to its flexibility. The performance evaluation of the proposed solution shows a possible enhancement of the message error rate by several orders of magnitude, while the decrease in network utilization stays at a reasonable level.