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Real-Time Computing Systems and Applications, 1998. Proceedings. Fifth International Conference on

Date 27-29 Oct. 1998

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Displaying Results 1 - 25 of 41
  • Proceedings Fifth International Conference on Real-Time Computing Systems and Applications (Cat. No.98EX236)

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  • Author index

    Page(s): 311 - 312
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    Freely Available from IEEE
  • Integrated dynamic scheduling of hard and QoS degradable real-time tasks in multiprocessor systems

    Page(s): 127 - 136
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    Many time critical applications require predictable performance and tasks in these applications have deadlines to be met. For tasks with hard deadlines, a deadline miss can be catastrophic, while for QoS degradable tasks (soft real time tasks) timely approximate results of poorer quality or occasional deadline misses are acceptable. Imprecise computation and (m,k) firm guarantee are two workload models that quantify the trade off between schedulability and result quality. We propose dynamic scheduling algorithms for integrated scheduling of real time tasks, represented by these workload models, in multiprocessor systems. The algorithms aim at improving the schedulability of tasks by exploiting the properties of these models in QoS degradation. We also show how the proposed algorithms can be adapted for integrated scheduling of multimedia streams and hard real time tasks, and demonstrate their effectiveness in quantifying QoS degradation. Through simulation, we evaluate the performance of these algorithms using the metrics-success ratio (measure of schedulability) and quality. Our simulation results show that one of the proposed algorithms, multilevel degradation algorithm, outperforms the others in terms of both the performance metrics View full abstract»

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  • A delay-constrained least-cost path routing protocol and the synthesis method

    Page(s): 58 - 65
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    Real-time communication services will be one of the most promising future applications in both the B-ISDN and Internet. In addition, real-time traffic usually utilizes a significant amount of resources while traversing the network. Thus there is the need for routing mechanisms which are able to satisfy requirements of both real-time traffic and efficient management of network resources. Firstly we discuss an issue of routing of real-time traffic subject to each end-to-end delay constraint and a path cost. Then, we describe a key concept which is taken into consideration of the requirements simultaneously. Based on the requirements, a delay constrained least-cost path problem is formulated. Since the problem is NP-hard, a heuristic method is proposed to solve the problem. The heuristic method can always find a delay-constrained path between a source node and a destination node, if there is such a path. Based on the heuristic method, an outline of the synthesis method for the delay-constrained least-cost path routing protocol is also presented View full abstract»

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  • Handling interrupts with static scheduling in an automotive vehicle control system

    Page(s): 158 - 165
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    The requirements of industrial applications only rarely permit the exclusive use of single paradigms in the development of real-time systems. Product cost, reuse of existing solutions, and efficiency require diverse, or even opposing methods to coexist or to be integrated. In this paper, we deal with one problem encountered during the development of a real-time system for motion control in automotive vehicles, the integration of static scheduling and interrupts. The user mandates pre run-time scheduling for a number of reasons, e.g., predictability, testability and low run-time overhead. However, the interrupt overhead cannot be ignored in a safety critical system, and therefore has to be accounted for when creating a static schedule. We propose a method that combines static scheduling and run-time interrupts by applying standard static scheduling techniques and exact analysis. The appropriateness of this method is underlined by successful industrial deployment View full abstract»

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  • On-line scheduling algorithms for reducing the largest weighted error incurred by imprecise tasks

    Page(s): 137 - 144
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    The paper proposes online scheduling algorithms that reduce the largest weighted error incurred by preemptive imprecise tasks running on a single processor system. The first one is a two level algorithm. The top level scheduling, which is executed whenever a new task arrives, determines the processing times to be allotted to tasks in such a way to minimize maximum weighted error as well as to minimize total error. The lower level algorithm actually allocates the processor to the tasks. The second algorithm extends the online algorithm studied by W.K. Shih and J.W.S. Liu (1992) by formalizing the top level algorithm mathematically. The numerical simulation shows that the proposed algorithm outperforms the previous works in the sense that it greatly reduces the largest weighted error View full abstract»

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  • Load adjustment and filtering based on process criticality

    Page(s): 3 - 10
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    This paper generalizes the load scaling techniques proposed in (Kuo and Mok, 1991) for fixed-priority real-time applications. A framework is proposed to adjust the system workload by relating the criticality and flexibility of a process to the resource allocation problem. A load adjustment procedure based on the approximation algorithm (Ni et al., 1997) is proposed to maximize the system profit in an on-line fashion. When the list of allowable configurations is implicitly given by scalable periodic processes, the corresponding load filtering problem is shown to be NP-complete. We also prove the upper bound of the system profit and provide a mechanism to balance the schedulability and the maximum profit of the system View full abstract»

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  • Continuous media filesystem services on a real-time JAVA server

    Page(s): 241 - 248
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    We investigate filesystem support for continuous media on the Java language. We describe a prototype implementation on a Real-Time Java Server, developed as an application level server on the Real-Time Mach microkernel environment. The Java virtual machine has been extended to support filesystem bandwidth reservation facilities existing on Real-Time Mach. Such facilities allow continuous media applications to specify their disk bandwidth usage requirements by creating a disk bandwidth reservation. The operating system, upon acceptance of the requests, internally enforces and guarantees such a share of the disk bandwidth for every active reservation. We present a performance evaluation, including both a synthetic application and real multimedia application based on a QuickTime video player which make use of real time Java threads and filesystem bandwidth reservation facilities. Our experiments conclude that the proposed filesystem extensions to the Java language are suitable for continuous media application requirements View full abstract»

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  • Design and implementation of an efficient I/O method for a real-time user level thread library

    Page(s): 117 - 120
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    We have developed a portable user level thread library RT-PTL on UNIX, which is intended to be used for soft real time processing, such as multimedia systems. A user level thread is known to be more efficient than a kernel level one because of its small context switch overhead. However user level thread has a restriction that if one thread issues a system call that forces the calling process to be entirely blocked (such as disk I/O operation), no other thread is runnable until the system call has completed. This characteristic is undesirable for real time processing. We present a method to overcome this restriction. Using this method, if one thread requests a system call such as disk I/O operation, only the thread that issues the request is blocked and other threads can continue execution. We have implemented this method and have confirmed by some experiments that the method is widely usable and is also efficient View full abstract»

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  • A worst case timing analysis technique for optimized programs

    Page(s): 151 - 157
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    We propose a technique to analyze the worst case execution times (WCETs) of optimized programs. Our work is based on a hierarchical timing analysis technique called the extended timing schema (ETS). A major hurdle in applying the ETS to optimized programs is the lack of correspondences in the control structure between the optimized machine code to be analyzed and the original source program written in a high-level programming language. We suggest a compiler-assisted approach where a timing analyzer relies on an optimizing compiler for a consistent hierarchical representation and an accurate source-level correspondence that are essential for accurate WCET analysis for optimized programs. In order to validate the proposed approach, we implemented a proof-of-concept version of a timing analyzer for a 256-bit VLIW processor and compared the analysis results with the simulation results. The experimental results show that the proposed solution can accurately predict the WCETs of highly-optimized VLIW programs View full abstract»

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  • Protocol synthesis from context-free processes using event structures

    Page(s): 173 - 180
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    We propose a protocol synthesis method based on a partial order model (called event structures) for the class of context-free processes. First, we assign a unique name called event ID to every event executable by a given service specification. An event ID is a finite sequence of symbols derived from the context-free process specification. Then we show that some interesting sets of events are expressible by regular expressions on symbols, and that the event structure can be finitely represented by a set of relations among the regular expressions. Finally, we present a method to derive a protocol specification which implements a given service specification on distributed nodes, by using the obtained finite representation of event structures. The derived protocol specification contains the minimum message exchanges necessary to ensure the partial order of events of the service specification View full abstract»

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  • Enhancing response times of end-to-end tasks using slack of local tasks

    Page(s): 21 - 28
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    This paper aims to enhance the response times of soft real-time end-to-end tasks while guaranteeing deadlines of hard real-time local tasks. Since the end-to-end task is comprised of multiple subtasks, we derive the intermediate timing attributes of subtasks taking into account precedence relations, and find the highest possible priorities of subtasks using the slack of hard real-time local tasks. The final result is a set of periodic tasks, which can be scheduled according to a fixed-priority scheme View full abstract»

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  • Real-time camera control for videoconferencing over the Internet

    Page(s): 121 - 124
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    In videoconferencing, which means a small group meeting, interactive distance learning and so on, there is a requirement to get required video at a remote site freely and easily by local control of a remote camera. However, there are some delays between camera control operations at a remote site and actual video images displayed on a local screen. Delays are caused by network delays between sender and receiver and by video compression delays. To operate a remote camera interactively, a user must control the device considering these delays. We describe these problems in the case of videoconferencing and develop a real time camera control system to solve them. Our approach does not involve reducing delays but showing delays for users by some indication under the current environment. With our proposed system, a user can easily operate a remote camera without considering network and compression delays. We use a new camera control protocol designed by us in our system. We also describe a prototype system and its evaluation used in distance learning View full abstract»

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  • On using similarity for resolving conflicts at commit in mixed distributed real-time databases

    Page(s): 277 - 285
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    In a distributed real-time database system (DRTDBS), transaction atomicity is ensured by commit protocol. If data conflict occurs between executing and committing transactions, system's performance will be affected. In this paper, based on the deadline driven conflict resolution (DDCR) approach proposed by Lam et al. (1997), we propose an enhancement called the DDCR with similarity (DDCR-S), to resolve the executing-committing conflicts in a DRTDBS with mixed requirements of criticality and consistency transactions. In the DDCR-S, conflicts involving transactions with looser consistency requirement, the notion of similarity is adopted so that a higher degree of concurrency can be achieved and at the same time the consistency requirements of the transactions can still be met. Simulation experiments have been performed and the results have shown that the use of DDCR-S can significantly improve the overall system performance View full abstract»

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  • A characterization of re-execution costs for real-time abort-oriented protocols

    Page(s): 286 - 292
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    Abort-oriented protocols for hard real-time systems were proposed mainly to cope with the situation when block-at-most-once property provided by pure locking protocols such as priority ceiling protocol and stack resource protocol is incapable of scheduling a given transaction set due to excessive blocking. The underlying principle is to abort a transaction if it causes other higher-priority transactions unschedulable due to excessive blocking. By aborting the lower-priority transaction, what we gain is reduced blocking for higher-priority transactions, but what we must pay for is to re-execute the aborted lower-priority transaction. To guarantee schedulability for the whole transaction set, we must put an upper bound on the re-execution costs. In this paper, we use a tree-structured transaction framework adapted from Chakravarthy et al. (1998) and we roll back aborted transactions partially in an attempt to more accurately characterize and to reduce re-execution costs for aborted transactions View full abstract»

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  • Task scheduling with feedback latency for real-time control systems

    Page(s): 37 - 41
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    A new task-scheduling algorithm with feedback latency is suggested for real-time control systems, which considers both point of views-control theoretic and real-time computing. Building a real-time control system has two steps in general. In the controller design stage, a control performance index is defined and a controller is designed which optimizes the given performance index while maintaining stability and rejecting disturbances. In the implementation stage, a set of controllers constitutes multiple control tasks, and scheduled to run on microprocessors, which should be schedulable with limited computing resources. The author reveals that the control performance depends not only on the control period but also on the feedback latency (latency from sensing, computation to actuation), which is revealed to have more impact. We formulate a new task-scheduling problem with a suitable control performance index including the feedback latency. An iterative search algorithm is suggested which is based on feedback latency computation method. An illustrative example demonstrated the applicability of the proposed method View full abstract»

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  • Partition scheduling in APEX runtime environment for embedded avionics software

    Page(s): 103 - 109
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    Advances in the computer technology encouraged the avionics industry to replace the federated design of control units with an integrated suite of control modules that share the computing resources. The new approach, which is called integrated modular avionics (IMA), can achieve substantial cost reduction in the development, operation and maintenance of airplanes. A set of guidelines has been developed by the avionics industry to facilitate the development and certification of integrated systems. Among them, a software architecture is recommended to address real time and fault tolerance requirements. According to the architecture, applications are classified into partitions supervised by an operating system executive. A general purpose application/executive (APEX) interface is defined which identifies the minimum functionality provided to the application software of an IMA system. To support the temporal partitioning between applications, APEX interface requires a deterministic cyclic scheduling of partitions at the O/S level and a fixed priority scheduling among processes within each partition. We propose a scheduling scheme for partitions in APEX. The scheme determines the frequency that each partition must be invoked and the assignment of processor capacity on every invocation. Then, a cyclic schedule at the O/S level can be constructed and all processes within each partition can meet their deadline requirements View full abstract»

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  • Multiprocessor scheduling of age constraint processes

    Page(s): 42 - 47
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    Real-time systems often consist of a number of independent processes which operate under an age constraint. In such systems, the maximum time from the start of process Li in cycle k to the end in cycle k+1 must not exceed the age constraint Ai for that process. Multiprocessors provide a scalable and cost-effective way of meeting the performance demands of such systems. The age constraint can be met using fixed priority scheduling and periods equal to Ai /2. However, this approach restricts the number of process sets which are schedulable. We define a method for obtaining process periods other than Ai/2. The periods are calculated in such a way that the age constraints are met. Our approach is better in the sense that a larger number of process sets can be scheduled compared to using periods equal to Ai/2 View full abstract»

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  • An architecture for a QOS-based mobile agent system

    Page(s): 145 - 148
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    Improving quality of service (QoS) has always been a challenging task. On one hand a user or an application makes subjective QoS requests; on the other hand, a number of host machines are ready to provide resources to satisfy these requests. The architecture we propose in the paper helps build an efficient link between a user and the resource providers. This architecture implements the mobile agent technology and the concept behind the logical disk interface introduced by M. Wiebren de Jonge et al. (1993) by clearly separating QoS negotiation and resource management. Here, the mobile agent system takes care of the QoS negotiation process and the virtual host manages-allocates, reserves and deallocates-needed resources. Mobile agents help reduce network traffic through remote programming and virtual hosts handle environmental changes transparently View full abstract»

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  • Dynamic transaction scheduling and reallocation in overloaded real-time database systems

    Page(s): 293 - 302
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    We introduce a novel scheduling architecture with a new algorithm for dynamically resolving transient overloads, that is executed when a new transaction cannot be admitted to the system due to scarce resources. The resolver algorithm generates a cost effective overload resolution plan which, in order to admit the new transaction, finds the required time by de-allocating time among the previously admitted but not yet completed transactions. Considering the cost efficiency of executing the plan and the importance of the new transaction a decision is made whether to execute the plan and admit the new transaction, or to reject it. We consider a multi-class transaction workload consisting of hard critical and firm transactions, where critical transactions have contingency transactions that can be invoked during overloads. We present a performance analysis showing to what degree the overload resolver enforces predictability and ensures the timeliness of critical transactions when handling extreme overload scenarios in real-time database systems View full abstract»

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  • Congestion control with two level rate control for continuous media traffic in network without QoS guarantee

    Page(s): 207 - 214
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    Recently, it is required to transfer continuous media over networks without QoS guarantee. In these networks, network congestion will cause transmission delay variance which degrades the quality of continuous media itself. This paper proposes a new protocol using congestion control with two level rate control in the data transfer level and the coding level. It introduces a TCP-like congestion control mechanism to the rate control of the data transfer level, which can detect the QoS change quickly, and adjust the coding rate of continuous media with a time interval long enough for its quality. The performance evaluation through software simulation with multiplexing continuous media traffic and TCP traffic shows that the proposed protocol works effectively in the case of network congestion View full abstract»

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  • Optimal scheduling for fault-tolerant and firm real-time systems

    Page(s): 223 - 231
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    Time redundancy is an effective method for achieving fault tolerance in a real time system, when space redundancy cannot be used for cost or weight constraints. The paper presents a fault tolerant scheduling algorithm for real time systems consisting of firm and hard periodic tasks. Firm tasks can occasionally skip one instance according to a predefined quality of service parameter, whereas hard tasks include a primary and a backup job. The proposed scheduling algorithm ensures that each task instance is satisfied within its timing constraints by either the primary or the backup job. Moreover the algorithm maximizes the processor idle time available for processing primary jobs and automatically reclaims the spare time saved by deallocating backup jobs. A very interesting feature of the algorithm is that it can be tuned to balance performance versus complexity, so easily conforming to application's requirements View full abstract»

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  • A bandwidth reservation algorithm for multi-application systems

    Page(s): 77 - 82
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    The paper focuses on the problem of providing efficient run time support for different applications running on a real time system. The goal of our research is to develop a scheduling algorithm to allow independent applications to coexist on the same system. In order to meet the requested QoS, we assign each application a minimum bandwidth and guarantee that it never demands more. This algorithm does not require the exact knowledge of the execution times and interarrival times of the application tasks: hence, it is especially suited for soft real time and multimedia applications View full abstract»

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  • Analysis of real-time backplane bus network based on write posting

    Page(s): 166 - 169
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    The backplane bus network protocol is a mechanism to facilitate the standard networking on the backplane bus. Usually a link-level network protocol is designed and implemented to provide the bus networking. In this paper we introduce a scheduling analysis for real-time communication in the backplane network. Unlike traditional communication analysis, we must consider the write posting, a feature of the bus interface which improves the overall schedulability dramatically. For an exact real-time analysis, a methodology is also developed to model the timing behavior of the bus View full abstract»

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  • Simulation and tracing of hybrid task sets on distributed systems

    Page(s): 249 - 256
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    This paper describes a tool for the design, simulation and analysis of real-time systems, ranging from simple scenarios with a few types of tasks on a single node to very complex architectures consisting of multiple nodes interconnected with a network and sharing a set of hardware and software resources. The tool is based on a discrete event simulation library, a scripting language describing the system load and the relevant measures, and a graphical interface providing user-friendly interaction with the simulator View full abstract»

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