An Optimization Framework for Real-Time Systems with Sustainable Schedulability Analysis

There is a growing interest in adopting object technologies for the development of real-time control systems. Several commercial tools, currently available, provide object-oriented modeling and design support for real-time control systems. While these products provide many useful facilities, such as visualization tools and automatic code generation, they are all weak in addressing the central characteristic of real-time control systems design, i.e., providing support for a designer to reason about timeliness properties. We believe an approach that integrates the advancements in both object modeling and design methods and real-time scheduling theory is the key to successful use of object technology for real-time software. Surprisingly several past approaches to integrate the two either restrict the object models, or do not allow sophisticated schedulability analysis techniques. This study shows how schedulability analysis can be integrated with UML for Real-Time (UML-RT) to deal with timing properties in real time control systems. More specifically, we develop the schedulability and feasibility analysis modeling for the external messages that may suffer release jitter due to being dispatched by a tick driven scheduler in real-time control system and we also develop the scheduliablity modeling for sporadic activities, where messages arrive sporadically then execute periodically for some bounded time. This method can be used to cope with timing constraints in realistic and complex real-time control systems. Using this method, a designer can quickly evaluate the impact of various implementation decisions on schedulability. In conjunction with automatic code-generation, we believe that this will greatly streamline the design and development of real-time control systems software.

Edge computing has been introduced as a promising technology for real-time video streaming systems. However, due to the lack of automatic incentives and the limitation of resources, traditional edge computing performs poorly in nowadays scenarios. To handle these two challenges, we propose a framework of Joint Incentive design and Resource Allocation (JIRA) for edge-based real-time video streaming systems. Technically, to ensure the trust and automatic distribution of incentives, we develop a novel smart contract based incentive mechanism and implement a prototype. Meanwhile, we propose an efficient online algorithm, i.e., JIRA, which dynamically adjusts compression ratio, offloading decision, and resource allocation to achieve performance optimization for video streaming under long-term latency and resource constraints. Specifically, JIRA is based on Lyapunov optimization, which decomposes the challenging long-term decision problem into a series of real-time optimization problems. Then we propose a multi-cut <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Generalized Benders Decomposition</i> based algorithm (MGA) to tackle the non-convexity of the decomposed problem. Through rigorous theoretical analysis, we prove the performance bound of JIRA. Extensive simulations demonstrate that the proposed schemes can achieve an efficient trade-off between accuracy performance and energy consumption.

The most important and necessary properties of embedded real-time systems, and the ways to achieve them, are explored. The basic and most important domains of real-time systems design are dealt with, starting with the processor and system hardware architectures, over operating systems, tasking and scheduling, high-level real-time programming languages, worst case execution time and schedulability analysis, to application design engineering and safety critical applications. Common misconceptions which are still strongly present in the control systems design are identified, guidelines for the consistent implementation are proposed and sample solutions in certain areas are presented.

Embedded systems are often subject to constraints that require determinism to ensure that task deadlines are met. Such systems are referred to as real-time systems. Schedulability analysis provides a firm basis to ensure that tasks meet their deadlines for which knowledge of worst-case execution time (WCET) bounds is a critical piece of information. Static timing analysis techniques are used to derive these WCET bounds. A limiting factor for designing realtime systems is the class of processors that can be used. Typically, modern, complex processor pipelines cannot be used in real-time systems design. Contemporary processors with their advanced architectural features, such as out-of-order execution, branch prediction, speculation, prefetching, etc., cannot be statically analyzed to obtain tight WCET bounds for tasks. This is caused by the non-determinism of these features, which surfaces in full only at runtime. In this paper, we introduce a new paradigm to perform timing analysis of tasks for real-time systems running on modern processor architectures. We propose minor enhancements to the processor architecture to enable this process. These features, on interaction with software modules, are able to obtain tight, accurate timing analysis results for modern processors. We also briefly present analysis techniques that, combined with our timing analysis methods, reduce the complexity of worst-case estimations for loops. To the best of our knowledge, this method of constant interactions between hardware and software to calculate WCET bounds for out-of-order processors is the first of its kind.

Many real-time tasks, particularly control tasks, can accommodate occasional missed deadlines thanks to robust algorithms. These tasks can be effectively modeled using the weakly-hard model, which specifies the maximum number of tolerable deadline misses, denoted as mi, within a sequence of Ki executions. Research indicates that utilizing the weakly-hard model can significantly reduce the over-provisioning typically required in the design of real-time systems. Therefore, different scheduling algorithms and schedulability analyses have been proposed in the last few years. However, state-of-the-art scheduling analyses do not scale with larger values of Ki. We present a new job-level fixed priority scheduling algorithm whose schedulability analysis scales with Ki. Furthermore, our scheduling algorithm leverages the tolerable continuous deadline misses to assigning priorities to jobs. Schedulability analyses show that the computation time of our analysis is up to 100 times faster comparing to the approaches in literature improving also the schedulability ratio for total utilization of 0.9.

Real-time multiprocessor systems have an increasing importance in current technology and are the source of innovations to build new applications that require high levels of computations (in for example, industrial processes, transportation, telecommunications, multimedia and medical equipment). In the context of real-time systems, it is not sufficient to prove the correctness of applications in term of results but also that those results are delivered in time. The following papers are extended, peer-reviewed, journal-versions of papers focusing on multiprocessor systems that have been selected by the conference program committee of the 19th Real-Time and Network Systems Conference (RTNS’2011) for their high quality. RTNS’2011 was held in Nantes, France in September 2011. The annual RTNS conference is mainly focused on the following topics: realtime system design and analysis; infrastructure and hardware for real-time systems; and real-time applications in the automotive, avionics, telecommunications, process control and the multimedia industries. Each paper was extended to add significant extra material and the resulting papers were re-reviewed and subject to the usual editorial process. The result is a special issue that we hope will be of interest to the real-time community. In recent years, multiprocessor architectures have become a firm favorite with the real-time community, and multicore processors are found in products ranging from small portable cell phones to large computer servers. New scheduling approaches

Structural Control of Probabilistic Boolean Networks and Its Application to Design of Real-Time Pricing Systems

Systems development has often resulted as a hit-or-miss proposition before the advent of standardized analysis and design languages providing blueprints understood by both software and systems engineers. This paved the way for modeling cyber-physical systems using established, yet evolving standardized notation widely accepted by industry. In the past, system analysts would try to assess the needs of their clients, generate a requirements analysis in some notation that the analyst understood (but not always the client), give that analysis to a programmer or team of programmers, and hope that the final product was the system the client wanted (Schmuller, 2003). However, advances in UML and SysML have created new pathways to the design process when combined with Concurrent Object Modeling and Architectural Design Method (COMET) methodology that can assist in the realm of complex embedded system design for next generation cyber-physical systems (Rajhans, 2009). In order for product development to meet a desired need, communicating the vision to the developers is of utmost importance. The UML is a visual modeling language that enables system builders to create blueprints that capture their design intentions in a standardized format for effective communication of engineering detail. The paper reviews some key benefits of using UML and SysML during the product development process with COMET. The UML process steps are briefly described, followed by an introduction to the SysML language which is an extension of the UML. The paper provides a process review of embedded system development using SysML for systems engineering that can be useful for modeling aspects of cyber-physical system development during integrated product development. Realizing the fact that SysML may be considered too generic to address embedded and real-time system design, the paper provides a brief review of COMET, a UML based method for the development of concurrent applications, in particular distributed and real-time applications (Gomaa, 2008). The Artificial Intelligence Design Framework introduced as part of the thesis work supported by NASA (Tanik, 2006) can be adapted to cyber-physical system design. The published book detailing the AIDF called Architecting Automated Design Systems is based on this thesis work (Tanik, 2008) and is being used as a basis for supporting cyber-physical system design using artificial intelligence decision support with many application areas, including complex safety-critical medical and space systems design. This journal paper establishes the link between the conference paper on integrated product development (Tanik, 2010), and the previous work on the PhD thesis completed in 2006 that relates to cyber-physical system design frameworks.

We investigate whether fast failure detectors can be useful--and if so by how much--in the design of real-time fault-tolerant systems. Specifically, we show how fast failure detectors can speed up consensus and fault-tolerant broadcasts, by providing fast algorithms and deriving some matching lower bounds, for synchronous systems with crashes. These results show that a fast failure detector service (implemented using specialized hardware or expedited message delivery) can be an important tool in the design of real-time mission-critical systems.

This paper examines a class of real-time control systems in which each control task triggers its next release based on the value of the last sampled state. Prior work used simulations to demonstrate that self-triggered control systems can be remarkably robust to task delay. This paper derives bounds on a task's sampling period and deadline to quantify how robust the control system's performance will be to variations in these parameters. In particular we establish inequality constraints on a control task's period and deadline whose satisfaction ensures that the closed-loop system's induced L 2 gain lies below a specified performance threshold. The results apply to linear time-invariant systems driven by external disturbances whose magnitude is bounded by a linear function of the system state's norm. The plant is regulated by a full-information H infin controller. These results can serve as the basis for the design of soft real-time systems that guarantee closed-loop control system performance at levels traditionally seen in hard real-time systems.

The central idea behind interface-based design is to describe components by a component interface. In contrast to a component description that describes what a component does, a component interface describes how a component can be used. A well designed component interface provides enough information to decide whether two or more components can work together properly in a system. In this work, we expand the idea of interface-based design to the area of real-time system design. Here, the term of 'working together properly' refers to questions like: Does the composed system satisfy all requested real-time properties such as delay and throughput constraints? For this, we introduce Real-Time Interfaces, that connect the principles of Real-Time Calculus with Interface-based Design. In contrast to traditional real-time system design, in interface-based real-time system design the compliance to real-time constraints is checked at composition time. This leads to faster design processes and partly removes the need for the classical binary search approach to find an economically dimensioned system. Further, interface-based real-time system design also benefits from the properties of incremental design and independent implementability.

There are two fundamental aspects in the design of the real-time systems: meeting real-time constraints and reliability. These two aspects are in conflict and are usually researched separately. To provide for fault-tolerance, there is the need for a greater execution time; but on the other hand, real-time systems require tasks to be completed by their deadlines. There is a clear and urgent need for mechanisms that are able to integrate the real-time and the reliability requirements. So, it is necessary to address the real-time and fault-tolerance requirements together during the design of the system. This would make the development of reliable real-time systems simple and efficient. Our approach is based on the idea that if the system is adaptable then reliability is easier to achieve. We have developed a mechanism, known as real-time recoverable action (RTR-action), which integrates the real-time and the reliability requirements.

Reliability-Aware Energy-Efficient Scheduling for (m, k)-Constrained Real-Time Systems Through Shared Time Slots

The paper deals with problems of high level modeling of real-time systems in system level languages. Main advantages of transaction level modeling in SystemC are emphasized. The universal kernel for functionality, communication and timing issues modeling is presented. The problem of multithreading is exemplified on sorting procedure implemented in multi-core microprocessor system. Advantages of system level approach to modeling and design of real-time systems are outlined.

In the design of real-time systems, tasks are often assigned priorities. Preemptive priority driven schedulers are used to schedule tasks to meet the timing requirements. Priority inversion is the term used to describe the situation when a higher priority task's execution is delayed by lower priority tasks. Priority inversion can occur when there is contention for resources among tasks of different priorities. The duration of priority inversion could be long enough to cause tasks to miss their deadlines. Priority inversion cannot be completely eliminated. However, it is important to identify sources of priority inversion and minimize the duration of priority inversion. IN the paper we present a comprehensive review of the problem of and solutions to unbounded priority inversion.