Fault‐driven stress testing of distributed real‐time software based on UML models

In a previous article, a stress testing methodology was reported to detect network traffic‐related Real‐Time (RT) faults in distributed RT systems based on the design UML model of a System Under Test (SUT). The stress methodology, referred to as Test LOcation‐driven Stress Testing (TLOST), aimed at increasing the chances of RT failures (violations in RT constraints) associated with a given stress test location (an network or a node under test). As demonstrated and experimented in this article, although TLOST is useful in stress testing different test locations (nodes and network, it does not guarantee to target (test) all RT constraints in an SUT. This is because the durations of message sequences bounded by some RT constraints might never be exercised (covered) by TLOST. A complementary stress test methodology is proposed in this article, which guarantees to target (cover) all RT constraints in an SUT and detect their potential RT faults (if any). Using a case study, this article shows that the new complementary methodology is capable of targeting the RT faults not detected by the previous test methodology. Copyright © 2009 John Wiley & Sons, Ltd.     

Optimizing data stream processing for large‐scale applications

Stream processing systems are designed to analyze data arriving in real time and using continuous queries and respond when a specific event or sequence of events are detected. An important aspect of these systems is Streaming Analytics, which facilitates statistical calculations on continuous data within the stream. These systems must be designed to handle high volumes of data, be scalable, and accommodate a multitude of long‐lived concurrently running analytics. The challenges involved in the development of stream processing include on‐the‐fly transformation of data streams to match the query needs of users and the ability to model stream transformations to detect overlaps and possibilities for optimizations and to specify a methodology to deliver optimizations. In particular, this work focuses on exposing data stream application internals in order to detect reusable parts and then consolidate applications to optimize computational resource usage. The Streaming Data Analytics Model presented in this paper adopts a declarative approach that enables processing and manipulation of data streams in a simple manner while facilitating powerful optimizations necessary for managing high volumes of streaming data in real time. An evaluation is provided to demonstrate in both theoretical and quantitative aspects the high performance offered by our approach.     

Guidelines for supporting real‐time multi‐touch applications

Multi‐touch driven user interfaces are becoming increasingly prevalent because of their intuitiveness and because of the reduction in the associated hardware costs. In recognition of this trend, multi‐touch software frameworks (MSFs) have begun to emerge. These frameworks abstract the low level issues of multi‐touch software development and deployment. MSFs therefore enable software developers who are unfamiliar with the complexities of multi‐touch software development to implement and deploy multi‐touch applications more easily. However, some multi‐touch applications have real‐time system requirements, and at present, no MSFs provide support for the development and deployment of such real‐time multi‐touch applications. The implication of this is that software developers are unable to take advantage of MSFs and, therefore, are forced to handle the complexities of multi‐touch and real‐time systems development and deployment for themselves in an ad hoc manner. The primary consequence of this is that the multi‐touch and/or real‐time aspects of the application may not function correctly. In this paper, guidelines are presented for applying real‐time system concepts to support the development and deployment of real‐time multi‐touch applications using MSFs. This serves to increase the probability that the application will meet its timing requirements while also reducing the complexity of the development and deployment process associated with multi‐touch applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Implementation of a TMO‐structured real‐time airplane‐landing simulator on a distributed computing environment

In real‐time simulation, the simulated system should display the same (or very close) timing behavior as the target system. The simulation accuracy is increased as the simulation time unit is decreased. Although there are several models for such systems, the TMO model is particularly appropriate due to its natural support for real‐time distributed object‐oriented programming. This paper discusses the results of the implementation of a real‐time airplane‐landing simulator on a distributed computing environment using the TMO model. Copyright © 2004 John Wiley & Sons, Ltd.     

Semi‐global stabilization of discrete‐time systems subject to non‐right invertible constraints

This paper investigates time‐invariant linear systems subject to input and state constraints. We study discrete‐time systems with full or partial constraints on both input and state. It has been shown earlier that the solvability conditions of stabilization problems are closely related to important concepts such as the right invertibility or non‐right invertibility of the constraints, the location of constraint invariant zeros, and the order of constraint infinite zeros. In this paper, for general time‐invariant linear systems with non‐right invertible constraints, necessary and sufficient conditions are developed under which semi‐global stabilization in the admissible set can be achieved by state feedback. Sufficient conditions are also developed for such a stabilization in the case where measurement feedback is used. Such sufficient conditions are almost necessary. Controllers for both state feedback and measurement feedback are constructed as well. Copyright © 2009 John Wiley & Sons, Ltd.     

MINIMIZING SERVICE DELAY OF APERIODIC TASKS IN DYNAMIC‐PRIORITY NON‐PREEMPTIVE HARD REAL‐TIME SYSTEMS

A scheduling technique is presented to minimize service delay of aperiodic tasks in hard real‐time systems that employ dynamic‐priority scheduling and do not allow task preemption. In a real‐time scheduling process, the execution of periodic tasks can be deferred as long as this does not cause other tasks to violate their time constraints. However, aperiodic tasks that usually have urgent missions should complete execution as early as possible. In this paper, it is assumed that aperiodic tasks also have time constraints. Thus, the problem of deciding whether an aperiodic task with an unpredictable arrival time can be scheduled successfully or not is difficult to solve because delaying periodic tasks may cause them to fail to meet their time constraints. We present a dynamic scheduling technique to solve this problem which makes use of the symmetric property of a schedule. The maximum possible idle slot is always reserved at every scheduling point so that aperiodic tasks can be serviced immediately if the reserved idle slot is big enough to service them. The proposed technique also maximizes utilization of idle slots by reserving them for the longest possible time span.     

Quad‐Rotor Modeling and Attitude Control Using State‐Dependent ARX Type Model

A state‐dependent autoregressive with exogenous variables (SD‐ARX) model whose functional coefficients are approximated by sets of radial basis function (RBF) networks is proposed to describe the dynamic behavior of a quad‐rotor in this paper. This model is identified offline and used as an internal predictor of a receding horizon predictive controller to address the quad‐rotor's attitude control issue. In addition, the physical constraints of the system have been also taken into account during the controller design process. The results of real‐time control on a quad‐rotor aircraft illustrate satisfactory modeling accuracy in a large operating range and good performance of control approach proposed in this paper.     

Reliability and time‐to‐failure bounds for discrete‐time constrained Markov jump linear systems

This paper presents a methodology to obtain a guaranteed‐reliability controller for constrained linear systems, which switch between different modes according to a Markov chain (Markov jump linear systems). Inside the classical maximal robust controllable set, there is 100% guarantee of never violating constraints at future time. However, outside such set, some sequences might make hitting constraints unavoidable for some disturbance realisations. A guaranteed‐reliability controller based on a greedy heuristic approach was proposed in an earlier work for disturbance‐free, robustly stabilisable Markov jump linear systems. Here, extensions are presented by, first, considering bounded disturbances and, second, presenting an iterative algorithm based on dynamic programming. In non‐stabilisable systems, reliability is zero; therefore, prior results cannot be applied; in this case, optimisation of a mean‐time‐to‐failure bound is proposed, via minor algorithm modifications. Optimality can be proved in the disturbance‐free, finitely generated case. Copyright © 2016 John Wiley & Sons, Ltd.     

A non‐smooth lower bound on ν

A non‐smooth optimization technique to directly compute a lower bound on the skew structured singular value ν is developed. As corroborated by several real‐world challenging applications, the proposed technique can provide tighter lower bounds when compared with currently available techniques. Moreover, in many cases, the determined lower bound equals the true value of ν. Thanks to the efficiency of the non‐smooth technique, the algorithm can be applied to problems involving even a significant number of uncertain parameters. Another appealing feature of the proposed non‐smooth approach is that the dimension of repeated scalar uncertainties in the overall structured uncertainty matrix has little impact on the computational time. The technique can be used to compute a lower bound on the structured singular value μ as well. Copyright © 2012 John Wiley & Sons, Ltd.     

InK‐Compact: In‐Kernel Stream Compaction and Its Application to Multi‐Kernel Data Visualization on General‐Purpose GPUs

Stream compaction is an important parallel computing primitive that produces a reduced (compacted) output stream consisting of only valid elements from an input stream containing both invalid and valid elements. Computing on this compacted stream rather than the mixed input stream leads to improvements in performance, load balancing and memory footprint. Stream compaction has numerous applications in a wide range of domains: e.g. deferred shading, isosurface extraction and surface voxelization in computer graphics and visualization. We present a novel In‐Kernel stream compaction method, where compaction is completed before leaving an operating kernel. This contrasts with conventional parallel compaction methods that require leaving the kernel and running a prefix sum kernel followed by a scatter kernel. We apply our compaction methods to ray‐tracing‐based visualization of volumetric data. We demonstrate that the proposed In‐Kernel compaction outperforms the standard out‐of‐kernel Thrust parallel‐scan method for performing stream compaction in this real‐world application. For the data visualization, we also propose a novel multi‐kernel ray‐tracing pipeline for increased thread coherency and show that it outperforms a conventional single‐kernel approach.     

Application of the Hirsch Generic Convergence Statement to the Set‐Point Regulation of Excitable‐Transparent‐Monotone Systems

Monotone systems are dynamical systems whose solutions preserve an ordering, relative to the initial data. This paper focuses on the set‐point regulation problem for excitable‐transparent‐monotone single‐input single‐output systems with well‐defined static characteristics. The suggested technique for designing a static feedback controller is inspired from the Hirsch Theorem for monotone autonomous systems. It is shown that the closed‐loop system is strongly monotone and its generic solution converges to the desired set‐point. A remark is given on the application of the suggested design methodology to delay systems, as well as to systems with reaction‐diffusion equations. A simulation example from the biological world demonstrates the effectiveness of the proposed control strategy in real applications.     

Continuous‐discrete filters for bearings‐only underwater target tracking problems

In this work, we develop a continuous‐discrete shifted Rayleigh filter (CD‐SRF) and a continuous‐discrete sparse‐grid Gauss‐Hermite filter (CD‐SGHF) for a real‐life passive underwater bearings‐only target tracking problem. The stochastic difference equation describing the process model is derived from its continuous equivalent using Ito‐Taylor expansion of order 1.5. The performance of the proposed filters is compared in terms of root mean square error (RMSE), track divergence and computational time. For a fair comparison, popular filters like the unscented Kalman filter (UKF), cubature Kalman filter (CKF) and Gauss–Hermite filter (GHF) are implemented. The effect of initial uncertainty, measurement noise covariance and sampling time on filtering accuracy is also studied. Finally, RMSEs of all the filters are evaluated in comparison with the Cramer–Rao lower bound (CRLB). From simulation results, it was observed that CD filters performed with higher accuracy than their discrete equivalents, with CD‐SRF proving to be the most accurate among all the filters.     

Experiences with component‐oriented technologies in nuclear power plant simulators

This paper proposes the application of modern component‐oriented technologies to the development of nuclear power plant simulators. On the one hand, as a significant improvement on previous simulators, the new kernel is based on the Common Component Architecture (CCA). The use of such a high‐performance computing oriented component technology, together with a novel algorithm to automatically resolve simulation data dependencies, allows the efficient execution of both parallel and sequential simulation models. On the other hand, RT‐CORBA is employed in the development of the rest of the applications that comprise the simulator. This real‐time communication middleware not only makes the management of communications easier, but also provides the applications with real‐time capabilities. Software components used in these two ways, simulation models integrating the kernel and distributed applications from which the simulator is comprised, improve the evolution and maintenance of the entire system, as well as promoting code reusability in other projects. Copyright © 2006 John Wiley & Sons, Ltd.     

KAL: kernel‐assisted non‐invasive memory leak tolerance with a general‐purpose memory allocator

Memory leaks are a continuing problem in the software developed with programming languages, such as C and C++. A recent approach adopted by some researchers is to tolerate leaks in the software application and to reclaim the leaked memory by use of specially constructed memory allocation routines. However, such routines replace the usual general‐purpose memory allocator and tend to be less efficient in speed and in memory utilization. We propose a new scheme which coexists with the existing memory allocation routines and which reclaims memory leaks. Our scheme identifies and reclaims leaked memory at the kernel level. There are some major advantages to our approach: (1) the application software does not need to be modified; (2) the application does not need to be suspended while leaked memory is reclaimed; (3) a remote host can be used to identify the leaked memory, thus minimizing impact on the application program's performance; and (4) our scheme does not degrade the service availability of the application while detecting and reclaiming memory leaks. We have implemented a prototype that works with the GNU C library and with the Linux kernel. Our prototype has been tested and evaluated with various real‐world applications. Our results show that the computational overhead of our approach is around 2% of that incurred by the conventional memory allocator in terms of throughput and average response time. We also verified that the prototype successfully suppressed address space expansion caused by memory leaks when the applications are run on synthetic workloads. Copyright © 2010 John Wiley & Sons, Ltd.     

Robust adaptive DSC of directly input‐coupled nonlinear systems with input unmodeled dynamics and time‐varying output constraints

In this paper, an adaptive robust dynamic surface control is proposed for a class of uncertain nonlinear interconnected systems with time‐varying output constraints and dynamic input and output coupling. The directly coupled inputs and control inputs are both of nonlinear input unmodeled dynamics. To counteract the instable impact of the nonlinear input unmodeled dynamics, normalization signals are designed on the basis of the convergence rates of their Lyapunov functions. With new state variables and control variables being defined, the real control inputs are obtained through solving the equations of intermediate control laws. The time‐varying constraints on output signals are implemented by introducing asymmetric barrier Lyapunov functions. In addition, dynamic signals and decentralized K‐filters are used to deal with the state unmodeled dynamics and to estimate the unmeasurable states, respectively. By the theoretical analysis, the signals in the closed‐loop system are proved to be semi‐globally uniformly ultimately bounded, and the output constraints are guaranteed simultaneously. A numerical example is provided to show the effectiveness of the proposed approach. Copyright © 2017 John Wiley & Sons, Ltd.     

A Low‐Memory,Straightforward and Fast Bilateral Filter Through Subsampling in Spatial Domain

In this work we present a new algorithm for accelerating the colour bilateral filter based on a subsampling strategy working in the spatial domain. The base idea is to use a suitable subset of samples of the entire kernel in order to obtain a good estimation of the exact filter values. The main advantages of the proposed approach are that it has an excellent trade‐off between visual quality and speed‐up, a very low memory overhead is required and it is straightforward to implement on the GPU allowing real‐time filtering. We show different applications of the proposed filter, in particular efficient cross‐bilateral filtering, real‐time edge‐aware image editing and fast video denoising. We compare our method against the state of the art in terms of image quality, time performance and memory usage.     

Input‐to‐state stability of min‐max MPC scheme for nonlinear time‐varying delay systems

This paper studies the robustness problem of the min–max model predictive control (MPC) scheme for constrained nonlinear time‐varying delay systems subject to bounded disturbances. The notion of the input‐to‐state stability (ISS) of nonlinear time‐delay systems is introduced. Then by using the Lyapunov–Krasovskii method, a delay‐dependent sufficient condition is derived to guarantee input‐to‐state practical stability (ISpS) of the closed‐loop system by way of nonlinear matrix inequalities (NLMI). In order to lessen the online computational demand, the non‐convex min‐max optimization problem is then converted to a minimization problem with linear matrix inequality (LMI) constraints and a suboptimal MPC algorithm is provided. Finally, an example of a truck‐trailer is used to illustrate the effectiveness of the proposed results. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Timing analysis of the PREEMPT RT Linux kernel

In the theory of real‐time scheduling, tasks are described by mathematical variables, which are used in analytical models in order to prove schedulability of the system. On real‐time Linux, tasks are computer programs, and Linux developers try to lower the latencies caused by the Linux kernel, trying to achieve faster response for the highest‐priority task. Although both seek temporal correctness, they use different abstractions, which end up separating these efforts in two different worlds, making it hard for the Linux practitioners to understand and apply the formally proved models to the Linux kernel and for theoretical researchers to apply the restrictions imposed by Linux for the theoretical models. This paper traces a parallel between the theory of response‐time analysis and the abstractions used in the Linux kernel. The contribution of this paper is threefold. We first identify the PREEMPT RT Linux kernel mechanisms that impact the timing of real‐time tasks and map these impacts to the main abstractions used by the real‐time scheduling theory. Then, we describe a customized trace tool, based on the existing trace infrastructure of the Linux kernel, that allows the measurement of the delays associated with the main abstractions of the real‐time scheduling theory. Finally, we use this customized trace tool to characterize the timing lines resulting from the behavior of the PREEMPT RT Linux kernel. Copyright © 2015 John Wiley & Sons, Ltd.     

HARTEX—a safe real‐time kernel for distributed computer control systems

A hard real‐time kernel is presented for distributed computer control systems (DCCS), highlighting a number of novel features, such as integrated scheduling of hard and soft real‐time tasks as well as tasks and resources; high‐performance time management supporting safe DCCS operation in a hard real‐time environment; synchronization and communication featuring event notification via vector semaphores and transparent communication through implicit (content‐oriented) message addressing. Conventional queues have been substituted by Boolean vectors and vector processing techniques throughout the kernel, resulting in efficient and highly deterministic behaviour, which is characterized by very low overhead and constant execution time of kernel operations, independent of the number of tasks involved. Copyright © 2001 John Wiley & Sons, Ltd.     

Temporal Coherence Methods in Real‐Time Rendering

Nowadays, there is a strong trend towards rendering to higher‐resolution displays and at high frame rates. This development aims at delivering more detail and better accuracy, but it also comes at a significant cost. Although graphics cards continue to evolve with an ever‐increasing amount of computational power, the speed gain is easily counteracted by increasingly complex and sophisticated shading computations. For real‐time applications, the direct consequence is that image resolution and temporal resolution are often the first candidates to bow to the performance constraints (e.g. although full HD is possible, PS3 and XBox often render at lower resolutions). In order to achieve high‐quality rendering at a lower cost, one can exploit temporal coherence (TC). The underlying observation is that a higher resolution and frame rate do not necessarily imply a much higher workload, but a larger amount of redundancy and a higher potential for amortizing rendering over several frames. In this survey, we investigate methods that make use of this principle and provide practical and theoretical advice on how to exploit TC for performance optimization. These methods not only allow incorporating more computationally intensive shading effects into many existing applications, but also offer exciting opportunities for extending high‐end graphics applications to lower‐spec consumer‐level hardware. To this end, we first introduce the notion and main concepts of TC, including an overview of historical methods. We then describe a general approach, image‐space reprojection, with several implementation algorithms that facilitate reusing shading information across adjacent frames. We also discuss data‐reuse quality and performance related to reprojection techniques. Finally, in the second half of this survey, we demonstrate various applications that exploit TC in real‐time rendering.