Complex Real-time Systems Research Articles

Interval timed coloured Petri net: efficient construction of its state class space preserving linear properties

Abstract We consider here the interval timed coloured Petri net model (ITCPN). This model associates with each created token a time interval specifying when the token will become available and forces enabled transitions to occur as soon as possible. This model can simulate other timed Petri nets and allows to describe large and complex real-time systems. We propose a much more efficient contraction for its generally infinite state space than those developed in the literature. Our contraction approach captures all linear properties of the model and produces finite graphs for all bounded models.

Framing Effects: Implications in Complex Problem Solving Tasks

In decision-making literature, framing effects have been studied in a wide number of task and context conditions. In much of these studies, there is strong support that decision framing can result in inconsistent behavior among individuals. While much of the literature has been in static, one-time tasks, there is a dearth of studies in decision framing in complex problem solving tasks. This dearth in part can be attributed to an assumption that operators in complex environments are often well trained in decision-making routines, and as such, may not be vulnerable to framing effects. However, what is still unclear is whether trained operators are resistant to the effects of framing when they operate under non-routine conditions, and more importantly, what relation, information processing changes caused due to framing may have on the task performance of operators. The study reported here was conducted to answer these two questions. The outcome of this work is expected to have both theoretical and practical implication towards understanding individual's adaptive behavior and design of real time complex systems.

A modelling and simulation based process for dependable systems design

Complex real-time system design needs to address dependability requirements, such as safety, reliability, and security. We introduce a modelling and simulation based approach which allows for the analysis and prediction of dependability constraints. Dependability can be improved by making use of fault tolerance techniques. The de-facto example, in the real-time system literature, of a pump control system in a mining environment is used to demonstrate our model-based approach. In particular, the system is modelled using the Discrete EVent system Specification (DEVS) formalism, and then extended to incorporate fault tolerance mechanisms. The modularity of the DEVS formalism facilitates this extension. The simulation demonstrates that the employed fault tolerance techniques are effective. That is, the system performs satisfactorily despite the presence of faults. This approach also makes it possible to make an informed choice between different fault tolerance techniques. Performance metrics are used to measure the reliability and safety of the system, and to evaluate the dependability achieved by the design. In our model-based development process, modelling, simulation and eventual deployment of the system are seamlessly integrated.

Continuous Time Model Predictive Control for a Magnetic Bearing System

The nature of active magnetic bearings has many advantages over the conven- tional bearing, as its operation is energy e-cient and potentially leads to cleaner and noise-free environment. However, the successful operation of an active magnetic bearing system requires a complex real-time control system, because of its unstable characteristics, as well as its nature of being a multi-input and multi-output system. This paper presents design and implementation of a continuous time model predictive control algorithm (CMPC) to an active magnetic bearing sys- tem (AMB). In this application, the plant continuous time model is identifled from experimental data using prediction error method. The control performance of this algorithm is studied using an experimental AMB laboratory system. A host-target development environment of real-time digital control system with hardware in the loop (HIL) is implemented and demonstrated by controlling a nonlinear, open-loop unstable, and multivariable magnetic levitation device.

The dynamic checking of complex real time system

The paper presents an dynamic execution model of complex real-time software based on requirement description model RTRSM, and then propose a checking method based on configuration covering and its corresponding algorithm. This checking method can check the execution situations between parallel elements in a dynamic execution step of real-time software systems. It also can check all the states and transitions which assure the completeness of checking. In the end, related theorem is proofed.

INTEGRATING SCHEDULABILITY ANALYSIS WITH UML-RT

The use of object-oriented techniques and methodologies to design real-time control systems appears to be necessary in order to deal with the increasing complexity of such systems. Recently, many object-oriented methods have been used for the modelling and designing of real-time control systems. We believe an approach that integrates the advancements in both object modelling and design methods, and real-time scheduling theory is a key to the successful use of object-oriented technology for real-time software. However, past approaches to integrate the two either have restricted the object models, or did not allow sophisticated schedulability analysis techniques. In this paper, we show the manner in which schedulability analysis can be integrated with object-oriented design; we develop the schedulability and feasibility analysis method for 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 schedulability method for sporadic activities, where messages arrive sporadically and are then executed periodically for some bounded time. This method can be used to cope with timing constraints in complex real-time control systems.

PHYSICAL ROBOT AGENTS: COORDINATED INTELLIGENT AND RATIONAL AGENTS FOR COLLABORATIVE ROBOTS

This paper reports on ongoing research to design coordination and cooperation ubiquitous to the control and tasking of multiple heterogeneous physical robot agents (PRAs) using a real-time agent architecture. The primary objective of the work presented here is to develop a real-time agent architecture and a distributed architectural framework that enables multiple PRAs to coordinate time-constrained high-level tasks in a collaborative manner. At the abstract level, we identify two layers, cognitive and action, based on the type of the PRA's responsibilities. At the cognitive layer we propose an extended version of the coordinated, intelligent rational agent (CIR-agent) model for complex real-time systems. The architecture facilitates integration between the cognitive layer and the action layer through the controller and functional modules. Our architecture also recognizes the coexistence of agent-oriented frameworks, such as JADE, and non-agent frameworks, like CORBA, to accommodate the cognitive and the action layers respectively.

A generic framework for modeling heterogeneous real-time systems

Complex real-time systems usually consist of heterogeneous components. These components interact with different semantics. Modeling these systems normally need integrating several domain-specific tools such as UML, Simulink. But interchanging data between these tools is very difficult. UML is a standard modeling language for object-oriented software development, used more and more in real-time domain. It provides several extensibility mechanisms to allow modeling special domains. This paper presents a generic framework, which is based on UML notations and metamodels, for heterogeneous modeling real-time systems. So engineers from different domains can work together on a unified platform.

Documentation driven development for complex real-time systems

This work presents a novel approach for development of complex real-time systems, called the documentation-driven development (DDD) approach. This approach can enhance integration of computer aided software development activities, which encompass the entire life cycle. DDD will provide a mechanism to monitor and quickly respond to changes in requirements and provide a friendly communication and collaboration environment to enable different stakeholders to be easily involved in development processes and, therefore, significantly improve the agility of software development for complex real-time systems. DDD will also support automated software generation based on a computational model and some relevant techniques. DDD includes two main parts: a documentation management system (DMS) and a process measurement system (PMS). DMS will create, organize, monitor, analyze, and transform all documentation associated with the software development process. PMS will monitor the frequent changes in requirements and assess the effort and success possibility of development. A case study was conducted by a tool set that realized part of the proposed approach.

Real-Time Operating Systems

Real-time operating systems are an integral part of complex real-time systems. Three general categories of real-time operating systems exist: small, proprietary kernels, real-time extensions to commercial timesharing operating systems, and research kernels. This paper discusses each of these areas focusing on how each of these classes deal with predictability. It is argued that the small, proprietary kernels are predictable, but offer little help to the real-time systems designer and implementor in producing predictable applications. Real-time versions of commercial operating systems like UNIX and Mach offer greater implementation support, but are, in general, NOT predictable themselves nor offer enough support to applications which require predictability. This, of course, does not mean that there is no way to achieve predictability with these operating systems. It is possible to achieve predictability by very careful design, by using a very limited subset of the overall features provided, and by proving that the features being used for predictability cannot in any way be impacted by any other part of the system. Finally, research kernels are attempting to provide greater design, implementation and evaluation support together with predictability for both the operating system and the application.

Broadcast MSCs

Abstract. Message sequence charts (MSCs) have proven to be a useful modeling technique especially within the requirements analysis phase of software development. MSCs, however, do not support the concept of broadcast communication, which is frequently used in technical applications. In this paper, we present an extension to MSCs for the modeling of broadcast interaction scenarios. Based on the mathematical framework of timed streams we also introduce a semantics for broadcast MSCs. We thoroughly discuss methodological benefits and semantic properties of this approach, consider alternative solutions, and address its scaleability with respect to complex real-time systems applications.

Extending UML-RT for Control System Modeling

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.

Timed state space analysis of real-time preemptive systems

A modeling notation is introduced which extends time Petri nets with an additional mechanism of resource assignment making the progress of timed transitions be dependent on the availability of a set of preemptable resources. The resulting notation, which we call preemptive time Petri nets, permits natural description of complex real-time systems running under preemptive scheduling, with periodic, sporadic, and one-shot processes, with nondeterministic execution times, with semaphore synchronizations and precedence relations deriving from internal task sequentialization and from interprocess communication, running on multiple processors. A state space analysis technique is presented which supports the validation of preemptive time Petri net models, combining tight schedulability analysis with exhaustive verification of the correctness of logical sequencing. The analysis technique partitions the state space in equivalence classes in which timing constraints are represented in the form of difference bounds matrixes. This permits it to maintain a polynomial complexity in the representation and derivation of state classes, but it does not tightly encompass the constraints deriving from preemptive behavior, thus producing an enlarged representation of the state space. False behaviors deriving from the approximation can be cleaned-up through an algorithm which provides a necessary and sufficient condition for the feasibility of a behavior along with a tight estimation of its timing profile.

Analysis of the MPEG-2 Encoding Algorithm with ROSA

The authors present both the specification and a performance analysis of the MPEG2 algorithm for video encoding, by using the Stochastic Process Algebra ROSA. This process algebra is a very general framework for describing and analyzing more complex Real Time Systems than the one presented. Some interesting results about the temporal behaviour of the algorithm and an immediate estimation of benefits when having a twin-processors platform have been obtained.

Software architecture supporting integrated real-time systems

To achieve reliability, reusability, and cost reduction, a significant trend in building large complex real-time systems is to integrate separate application modules of different criticalities in a common hardware platform. An essential requirement of integrated real-time systems is to guarantee spatial and temporal partitioning among applications in order to ensure an exclusive access of physical and temporal resources to the applications. In this paper we propose software architecture, implemented as SPIRIT-μKernel, for strongly partitioned integrated real-time systems. The SPIRIT-μKernel has been designed and implemented based on a two-level hierarchical scheduling methodology such that the real-time constraints of each application can be guaranteed. To demonstrate the feasibility of the SPIRIT-μKernel, we have ported two real-time operating systems (RTOS), WindRiver’s VxWorks and Cygnus’s eCos, on the top of the microkernel. Thus, different RTOS can be applied in various partitions to provide required features for each application. Based on the measured performance results, the SPIRIT-μKernel architecture is practical and appealing due to its low overheads of kernel services and the support for dependable integration of real-time applications via scheduling algorithm.

Parallel and Distributed Real-Time Systems

Parallel and Distributed Real-Time Systems

A Framework for using benefit functions in complex real-time systems

Researchers are currently investigating applying benefit, or utility functions for allocating resources in limited, soft real-time systems [1, 2, 3]. While the future of real-time computing research and practice will likely exploit the utility of benefit-based models, this will not occur until a suitable system level benefit framework has been defined. This paper provides an overview of ongoing work to develop such an initial framework that can formalize the use of benefit functions in complex real-time systems. It is easily shown that this framework can support traditional hard/firm/soft real-time paradigms as well as support newer proposed models for future real-time operation [4, 5]. We also show that our proposed framework unifies composition of benefit values derived from heterogeneous perspectives, including those derived from the application perspective. [1] E. D. Jensen, C. D. Locke and H. Tokuda, A Time-Driven Scheduling Model for Real-Time Operating Systems, in Proceedings of the IEEE Real-Time Systems Symposium, pp. 112–122, IEEE CS Press, 1985. [2] S. A. Brandt and G. J. Nutt, Flexible Soft Real-Time Processing in Middleware, in Journal of Real-Time Systems, Kluwer, 22(1,2):77–118, January–March 2002. [3] L. R. Welch, B. Ravindran, B. Shirazi and C. Bruggeman, Specification and analysis of dynamic, distributed real-time systems, in Proceedings of the IEEE Real-Time Systems Symposium, pp. 72–81, IEEE CS Press, 1998. [4] E. Lee, What's Ahead for Embedded Software? in IEEE Computer, pp. 18–26, Sept. 2000. [5] J. Hill, R. Szewczyk, A. Woo, S. Hollar, D. Culler and K. Pister, System Architecture Directions for Networked Sensors, in Proceedings of the 9th International Conference on Architectural Support for Programming Languages and Operating Systems (ASPLOS IX), pp. 93–104, Nov. 2000.

FRAMEWORK FOR DEVELOPING REAL-TIME MOBILE ROBOTIC APPLICATIONS BASED ON BEHAVIOURAL MODELS

In complex real-time control systems such as autonomous mobile robotic systems, the use of development tools for the design, analysis and validation of robotic applications is highly desirable, specially to improve the robot performances and to avoid early software and hardware design faults. This paper presents a framework for developing real-time mobile robotic applications. The main feature of the environment is that it permits the integrated analysis and validation of the functional behaviour of the robot (i.e. robot carrying out its plans) and the guarantee of the temporal constraints of the system processes (i.e. reactive and deliberative process execution). The verification of the correctness of the functional requirements is supported by means of a robot simulation tool that reflects the progress of the system at the application level. Likewise, a temporal analysis tool, based on scheduling analytical techniques, guarantees the schedulability of the system load at the execution level. The usefulness of the development tool is shown through design examples applied to mobile robotic applications.

FARM: A Feedback-Based Adaptive Resource Management For Complex Real-Time Systems and Application to Sensor Web

The increasing reliance on real-time technologies for building complex systems calls for e.cient dynamic resource management strategies. These strategies aim to achieve high resource utilization and allow graceful degradation in the face of unpredictable workload. In this paper, we present a novel resource management methodology, called Feedback-based Adaptive Resource Management (FARM), which is suited for complex real-time applications that has dynamic workload. We present a case study of one such complex system: Autonomous Hot Spot Convergence System (AHSCS) for sensor web, and apply our resource management solution to AHSCS. The FARM methodology combines the advantages of feedback-controlled scheduling, value-based scheduling, and path-based paradigm to provide a predictable, reliable, and robust services to complex real-time systems, such as AHSCS.

Using UML to Describe the Structural Architecture of Complex Real-time Systems

The architecture of a software system is fundamental to a successful realization and to supporting subsequent system evolution. In real-time control systems, it may strongly affect the controllability of the overall system. The paper describes an approach to modeling the structural aspects of the architectures of real-time systems using the industry standard Unified Modeling Language. Included is an example of the use of this approach to a standard architectural pattern used in many complex real-time systems.