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Real-Time Systems, 2000. Euromicro RTS 2000. 12th Euromicro Conference on

Date 19-21 June 2000

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  • Proceedings 12th Euromicro Conference on Real-Time Systems. Euromicro RTS 2000

    Publication Year: 2000
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  • Model-checking real-time control programs: verifying LEGO MINDSTORMSTM systems using UPPAAL

    Publication Year: 2000 , Page(s): 147 - 155
    Cited by:  Papers (4)
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    The authors present a method for automatic verification of real time control programs running on LEGO(R) RCXTM bricks using the verification tool UPPAAL. The control programs, consisting of a number of tasks running concurrently, are automatically translated into the timed automata model of UPPAAL. The fixed scheduling algorithm used by the LEGO(R) RCXTM processor is modeled in UPPAAL, and supply of similar (sufficient) timed automata models for the environment allows analysis of the overall real time system using the tools of UPPAAL. To illustrate our techniques, we have constructed, modeled and verified a machine for sorting LEGO(R) bricks by color. View full abstract»

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  • Author index

    Publication Year: 2000 , Page(s): 281
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    Freely Available from IEEE
  • Clock synchronization for wireless local area networks

    Publication Year: 2000 , Page(s): 183 - 189
    Cited by:  Papers (17)
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    High-precision clock synchronization is one of the most basic requirements in distributed real-time systems. This paper presents an enhanced clock synchronization protocol for wireless local area networks based on the IEEE 802.11 standard. Reducing the time-critical path of the protocol enhances the synchronization precision. As wireless communication links are inherently unreliable, special emphasis is put on fault tolerance. The protocol guarantees high precision even in the presence of message losses. The protocol is implemented in a Windows NT NDIS driver for Lucent WaveLAN cards. For this driver-level implementation, our measurements have shown that a precision of 150 μs is achieved View full abstract»

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  • The implementation of hierarchical schedulers in the RED-Linux scheduling framework

    Publication Year: 2000 , Page(s): 231 - 238
    Cited by:  Papers (5)
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    Hierarchical schedulers are useful to integrate different scheduling paradigms together. The original RED-Linux general scheduling framework does not support hierarchical schedulers efficiently because the dispatcher cannot tell whether a job is an aperiodic job or a real-time job. In the work reported in this paper, we add an extra parameter, the group number, to the RED-Linux scheduling framework in order to identify the type of jobs. This mechanism does not introduce any overhead to normal real-time tasks and only a constant overhead per job for hierarchical jobs. We discuss how to implement hierarchical schedulers and how to use this extension to support sporadic schedulers. We also discuss various versions of the sporadic server algorithm View full abstract»

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  • Scheduling algorithms for dynamic message streams with distance constraints in TDMA protocol

    Publication Year: 2000 , Page(s): 239 - 246
    Cited by:  Papers (9)
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    In many real-time communication applications, predictable and guaranteed timeliness is one of the critical components of the quality of service (QoS) requirements. In this paper, we propose a new real-time message model with both rate requirements and distance constraints. Two algorithms are presented to schedule dynamic real-time message streams in a TDMA (time division multiple access) frame based on different scheduling policies by making greedy choices or optimization choices. The performance of the two algorithms is evaluated and compared in terms of time complexity, acceptance ratio and scheduling jitter via simulation View full abstract»

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  • Elastic feedback control

    Publication Year: 2000 , Page(s): 121 - 128
    Cited by:  Papers (20)
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    In many real time control applications, the task periods are typically fixed and worst case execution times are used in schedulability analysis. With the advancement of robotics, flexible visual sensing using cameras has become a popular alternative to the use of embedded sensors. Unfortunately, the execution time of visual tracking varies greatly. In such environments, control tasks have a normally short computation time but also an occasional long computation time; therefore, the use of worst case execution time is inefficient for controlling performance optimization. Nevertheless, to maintain the control stability, we still need to guarantee the task set, even if the worst case arises. We propose an integrated approach to control performance optimization and task scheduling for control applications where the execution time of each task can vary greatly. We create an innovative approach to elastic control that allows us to fully utilize the processor to optimize the control performance and yet guarantee the schedulability of all tasks under worst case conditions View full abstract»

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  • Worst-case utilization bound for EDF scheduling on real-time multiprocessor systems

    Publication Year: 2000 , Page(s): 25 - 33
    Cited by:  Papers (50)
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    Presents the utilization bound for earliest deadline first (EDF) scheduling on homogeneous multiprocessor systems with partitioning strategies. Assuming that tasks are pre-emptively scheduled on each processor according to the EDF algorithm, and allocated according to the first-fit (FF) heuristic, we prove that the worst-case achievable utilization is 0.5(n+1), where n is the number of processors. This bound is valid for arbitrary utilization factors. Moreover, if all the tasks have utilization factors under a value α, the previous bound is raised, and the new utilization bound considering α is calculated. In addition, we prove that no uniprocessor scheduling algorithm/allocation algorithm pair can provide a higher worst-case achievable utilization than that of EDF-FF. Finally, simulation provides the average-case achievable utilization for EDF-FF View full abstract»

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  • Modelling and analysis of a commercial field bus protocol

    Publication Year: 2000 , Page(s): 165 - 172
    Cited by:  Papers (8)
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    We report on an industrial application of UPPAAL, in which a commercial field bus protocol (AF100) is modelled and analysed using the tool. During the case study, a number of imperfections in the protocol logic and its implementation are found and the error sources are debugged based on abstract models of the protocol; respective improvements have been suggested. The authors summarize their experiences in dealing with the complexity of the protocol using various modelling and abstraction features provided in UPPAAL. As an example, they study the bus coupler of AF100, which serves as the data link layer of the protocol View full abstract»

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  • Worst-case execution times analysis of MPEG-2 decoding

    Publication Year: 2000 , Page(s): 73 - 80
    Cited by:  Papers (5)
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    Presents the first worst-case execution times (WCET) analysis of MPEG decoding. Solutions for two scenarios-video-on-demand (VoD) and live-are presented, serving as examples for a variety of real-world applications. A significant reduction of over-estimations (down to 17%, including overheads) during WCET analysis of the live scenario can be achieved by using our new two-phase decoder with built-in WCET analysis, which can be universally applied. It is even possible to predict the exact execution times in the VoD scenario. This work is motivated by the fact that media streaming service providers are under great pressure to fulfil the quality of service promised to their customers, preferably in an efficient way View full abstract»

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  • Greedy reclamation of unused bandwidth in constant-bandwidth servers

    Publication Year: 2000 , Page(s): 193 - 200
    Cited by:  Papers (27)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    A framework for scheduling a number of different applications on a single shared pre-emptable processor is proposed, such that each application seems to be executing on a slower dedicated processor. A tradeoff is identified and evaluated between how precise a notion of real time (as measured by the granularity of its clock) an application needs to have supported on the one hand, and the added context-switch costs imposed by our scheduling framework on the other View full abstract»

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  • On adaptive control techniques in real-time resource allocation

    Publication Year: 2000 , Page(s): 129 - 136
    Cited by:  Papers (7)
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    A remarkable class of soft real time applications exhibits a very dynamical behaviour due to the variations in the treated data. Moreover, such programs have to be able to run on hundreds of different platforms. As a consequence, classical real time scheduling algorithms are not flexible enough since they are based on the exact knowledge of the tasks' timing parameters. Some of the approaches proposed so far in the literature guarantee temporal isolation, but they make a static assignment of resources to each task, which, once again, is based on an a priori knowledge. The authors propose a closed loop method for online adapting of the fraction of assigned resource to the task requirements. The approach is based on adaptive control techniques and has resulted in being effective in a significant set of real life experiments View full abstract»

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  • Early-release fair scheduling

    Publication Year: 2000 , Page(s): 35 - 43
    Cited by:  Papers (44)
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    Presents a variant of Pfair scheduling (S. Baruah et al., 1995, 1996), which we call early-release fair (ERfair) scheduling. Like conventional Pfair scheduling, ERfair scheduling algorithms can be applied to optimally schedule periodic tasks on a multiprocessor system in polynomial time. However, ERfair scheduling differs from Pfair scheduling in that it is work-conserving. As a result, average job response times may be much lower under ERfair scheduling than under Pfair scheduling, particularly in lightly loaded systems. In addition, run-time costs are lower under ERfair scheduling View full abstract»

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  • Running-modes of real-time systems: a case-study with mode-automata

    Publication Year: 2000 , Page(s): 257 - 264
    Cited by:  Papers (1)
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    Real-time systems, in particular regulation systems, are often specified using the notion of running modes. On the other hand, the family of synchronous languages has been very successful in offering formally defined languages and programming environments for safety-critical systems. We are particularly interested in the data-flow language Lustre, which is well-suited for the description of regulation systems. We propose to extend Lustre with a new construct devoted to the description of running modes in regulation systems. This language extension is based upon the mathematical model of mode automata. We now have a running implementation of this extension. In this paper, we comment on a case study proposed by Saab, and argue for the introduction of language features that are devoted to the expression of modes, from different points of view: readability, efficiency of the compiled sequential code, ability to transmit hints to verification tools, accurate evaluation of the worst-case execution time (WCET), static analysis of the resources used, etc View full abstract»

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  • Schedulability analysis for systems with data and control dependencies

    Publication Year: 2000 , Page(s): 201 - 208
    Cited by:  Papers (6)
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    Presents an approach to schedulability analysis for hard real-time systems with control and data dependencies. We consider distributed architectures consisting of multiple programmable processors, and the scheduling policy is based on a static priority pre-emptive strategy. Our model of the system captures both data and control dependencies, and the schedulability approach is able to reduce the pessimism of the analysis by using the knowledge about control and data dependencies. Extensive experiments as well as a real-life example demonstrate the efficiency of our approach View full abstract»

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  • Towards validated real-time software

    Publication Year: 2000 , Page(s): 157 - 164
    Cited by:  Papers (4)
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    We present a tool for the design and validation of embedded real time applications. The tool integrates two approaches: the use of the synchronous programming language, ESTEREL for design, and the application of model checking techniques for validation of real time properties. Validation is carried out on a global formal model (timed automata) taking into account the effective implementation of the application on the target hardware architecture as well as its external environment behavior View full abstract»

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  • Predicting computation time for advanced processor architectures

    Publication Year: 2000 , Page(s): 89 - 96
    Cited by:  Papers (2)
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    Estimating computation times using analysis techniques is always safe but is becoming prohibitively complex or pessimistic with modern processors. The only alternative approach is to use measurement, but this has the significant disadvantage of optimism - the largest value seen during testing may not be the largest experienced during deployment. In this paper, we subject data obtained from measurement to statistical analysis using the techniques of extreme value estimation. A simple case study is described and the approach is illustrated via this study which focuses on the superscalar technique of branch prediction. The approach is applicable to all forms of hardware-induced temporal variability View full abstract»

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  • Schedulability analysis of distributed hard real-time systems with multiple-event synchronization

    Publication Year: 2000 , Page(s): 15 - 24
    Cited by:  Papers (7)  |  Patents (1)
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    Presents a schedulability analysis technique for distributed hard real-time systems in which responses to different events may synchronize with each other. This technique uses a representation model for distributed systems that allows us to describe not only the task synchronization due to resource sharing, but also the activation due to combinations of events or the generation of several events by a single task. The model is representative of a large number of systems and is suitable for the treatment of message-passing systems or the client-server architecture. The analysis technique is based on the existing rate monotonic analysis (RMA) techniques for analyzing distributed real-time systems; it allows obtaining upper bounds for the worst-case response times of the system, thus allowing us to make guarantees about the fulfillment of the timing requirements that have been imposed View full abstract»

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  • Non pre-emptive scheduling of messages on SMTV token-passing networks

    Publication Year: 2000 , Page(s): 209 - 218
    Cited by:  Papers (4)
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    Fieldbus communication networks aim to interconnect sensors, actuators and controllers within distributed computer-controlled systems. Therefore, they constitute the foundation upon which real-time applications are to be implemented. A specific class of fieldbus communication networks is based on a simplified version of token-passing protocols, where each station may transfer, at most, a single message per token visit (SMTV). In this paper, we establish an analogy between non-preemptive task scheduling in single processors and the scheduling of messages on SMTV token-passing networks. Moreover, we clearly show that concepts such as blocking and interference in non-preemptive task scheduling have their counterparts in the scheduling of messages on SMTV token-passing networks. Based on this task/message scheduling analogy, we provide pre-run-time schedulability conditions for supporting real-time messages with SMTV token-passing networks. We provide both utilisation-based and response time tests to perform the pre-run-time schedulability analysis of real-time messages on SMTV token-passing networks, considering RM/DM (rate monotonic/deadline monotonic) and EDF (earliest deadline first) priority assignment schemes View full abstract»

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  • Integration of off-line scheduling and optimal control

    Publication Year: 2000 , Page(s): 137 - 143
    Cited by:  Papers (12)
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    A novel method for offline scheduling is proposed where the periodic task model does not contain the usual task period parameter. This is possible because the scheduling is integrated with control theory. A slot length defines the granularity of schedule and the optimal control theory tells us what the best offline static cyclic schedule is with respect to the overall system performance. The optimal control theory used here is periodic linear quadratic control and should be comprehensible to the control engineer versed in state space theory. The scheduled resource is fairly divided among the controllers by paying respect to their needs when rejecting disturbances acting on the plant View full abstract»

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  • Prototyping distributed multimedia systems using communicating real-time state machines

    Publication Year: 2000 , Page(s): 273 - 280
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    The paper describes a methodology for the development of real time systems and shows its application to the modeling, analysis and implementation of distributed multimedia systems. The methodology is centered on Communicating Real-Time State Machines as the modeling language and is supported by jCRSM, a Java2 based toolset. The latter provides a graphical environment for editing, testing, debugging and Java code generation of a prototyped system. Multimedia systems are particular real time systems which normally do not have hard deadlines to fulfill but only soft deadlines concerning the achievement of a user-defined level of quality of service. For instance, timing QoS parameters refer to jitter, skew and end-to-end delay, which are to be kept bounded throughout a multimedia session. QoS constraints are monitored by assertions on the recorded timestamped event histories. The paper reports some experimental results of a modeled remote multimedia presentation system View full abstract»

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  • An adaptable security manager for real-time transactions

    Publication Year: 2000 , Page(s): 63 - 70
    Cited by:  Papers (8)  |  Patents (3)
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    The rising demand for real-time services over networks, such as Web-based information services, requires new approaches for balancing competing demands on limited resources. The BeeHive database system proposes a novel solution to this need by the use of adaptive real time, fault tolerance, quality of service and security services based on rules embedded in individual objects. These rules prescribe tradeoffs of alternate levels of service (and cost) when resource contention becomes a problem. The approach momentarily trades off the level of security to achieve the required real-time performance. In many situations, this is an acceptable, and even preferred, solution. We have developed an adaptable security manager to provide alternate levels of communications security to multiple users and to dynamically adapt to real-time performance conditions. In this paper, we present the design and evaluation of the proposed security manager that utilizes the notion of adaptable security services View full abstract»

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  • Portable worst-case execution time analysis using Java Byte Code

    Publication Year: 2000 , Page(s): 81 - 88
    Cited by:  Papers (9)  |  Patents (1)
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    Addresses the problem of performing worst-case execution time (WCET) analysis of Java Byte Code (JBC), which may be generated from different compilers and from different source languages. The motivation for the framework presented is to provide WCET analysis which is portable and therefore more likely to be used in an industrial context. Two issues are addressed in this paper: how to extract data flow and control flow information from JBC programs, and how to provide a compiler-/language-independent mechanism to introduce WCET annotations in the source code. We show that an annotation mechanism based on calls to a static class with empty methods result in similar code when generated by Java or Ada compilers View full abstract»

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  • Designing inter-class concurrency control strategies for real-time database systems with mixed transactions

    Publication Year: 2000 , Page(s): 47 - 54
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    Although many efficient concurrency control protocols have been proposed for real-time database systems, they are mainly designed for those systems with a single type of real-time transaction. Due to the very different performance requirements of each type of real-time transaction, these proposed protocols may not be suitable for mixed real-time database systems (MRTDBSs), where different types of real-time transactions, and even non-real-time transactions, may co-exist in the systems at the same time. In this paper, we propose strategies for resolving data conflicts between different types of transactions in a MRTDBS so that their different performance requirements can be achieved and, at the same time, the overall system performance can be improved. The performance of the proposed strategies is evaluated and compared with a real-time optimistic approach. The performance of our proposed conflict resolution methods has also been investigated in a more realistic environment with a limited number of priority levels and disk-resident data items View full abstract»

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  • Tolerating faults while maximizing reward

    Publication Year: 2000 , Page(s): 219 - 226
    Cited by:  Papers (7)
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    The imprecise computation (IC) model is a general scheduling framework that is capable of expressing the precision vs. timeliness tradeoff involved in many current real-time applications. In that model, each task comprises mandatory and optional parts. While allowing greater scheduling flexibility, the mandatory parts in the IC model still have hard deadlines, and hence they must be completed before the task's deadline, even in the presence of faults. In this paper, we address fault-tolerant (FT) scheduling issues for IC tasks. First, we propose two recovery schemes, namely immediate recovery and delayed recovery. These schemes can be readily applied to provide fault tolerance to the mandatory parts by scheduling the optional parts appropriately for recovery operations. After deriving the necessary and sufficient conditions for both schemes, we consider the FT-optimality problem, i.e. generating a schedule which is FT and whose reward is maximum among all possible FT schedules. For immediate recovery, we present and prove the correctness of an efficient FT-optimal scheduling algorithm. For delayed recovery, we show that the FT-optimality problem is NP-hard, and thus is intractable View full abstract»

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