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Parallel and Distributed Real-Time Systems, 1997. Proceedings of the Joint Workshop on

Date 3-3 April 1997

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Displaying Results 1 - 25 of 43
  • Proceedings of 5th International Workshop on Parallel and Distributed Real-Time Systems and 3rd Workshop on Object-Oriented Real-Time Systems

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    Freely Available from IEEE
  • Author index

    Page(s): 327
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    Freely Available from IEEE
  • A transaction-based temporal data model for real-time databases

    Page(s): 149 - 158
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    We propose a real-time database model that deals with the temporal nature of data. Previous models assigned validity intervals with data items. A value of a data item is then only valid within the corresponding interval. In the new model, it is recognized that validity depends on the usage of the data item, therefore temporal validity is a characteristic of transactions, rather than of data items. The paper shows the influence of this different modeling on the expressiveness of the specification. It compares the transaction-based model with existing models that cover the same area, by looking at implementations that are based on these models View full abstract»

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  • Distributing time sensitive data in a COTS shared media environment

    Page(s): 53 - 62
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    Traditionally, the Navy has developed systems which distribute time-sensitive data using specialized components such as dedicated point-to-point communications links. Today, however the Navy is moving away from specialized solutions and toward Commercial-Off-the-Shelf (COTS) components to both keep up with the rapid pace of technology changes and to reduce system costs. COTS components are designed to meet needs of applications in the general commercial marketplace, not the specialized needs of real-time applications. This paper examines the ability of COTS workstations to distribute and process time sensitive data in a shared media environment. Several metrics are defined and then used to evaluate the performance of a simulated time sensitive data distribution and processing mechanism running on COTS workstations from Hewlett Packard, the Digital Equipment Corporation, and Sun Microsystems. The data collected is analyzed. COTS real-time operating system features are then used to tune the performance of the client and server components of the mechanism View full abstract»

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  • Platform-independent verification of real-time programs

    Page(s): 183 - 192
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    To include the specification of timing properties in distributed programs, we propose a method to extend existing programming languages with timing annotations. These annotations provide a similar abstraction from the execution platform as is normal for non-real-time languages. Hence they enable the construction of (hard) real-time programs which can be proved correct independently of any underlying execution platform. The realization of programs on a particular platform is considered as a separate phase where, e.g., scheduling is important. We illustrate the method by means of a simple programming language which is extended with timing annotations. A formal, axiomatic, semantics of the language constructs is defined. It is used to prove the correctness of a small example program View full abstract»

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  • Composing multiple-client-multiple-server synchronizations

    Page(s): 269 - 282
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    A considerable number of language mechanisms have been proposed during recent years, to specify and implement concurrent object-oriented programs. The major concern of these proposals is to design an expressive language that provides extensible concurrent processing and synchronization features. Almost all these efforts, however, have focused on the multiple-client-single-server model where each server determines its synchronization semantics without cooperating with other objects. We believe that object-oriented concurrent languages must not only support a single-server model, but cooperatively synchronizing servers as well. We refer to this as multi-server synchronization. We first classify multi-server synchronization into five categories. The intention is to define a framework for evaluating current approaches and identifying the requirements for designing new languages. In addition, we present a composable multi-server synchronization technique, adopting the concept of composition-filters View full abstract»

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  • Report on the case-study session [air defense system]

    Page(s): 105 - 107
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    As part of the call for papers for the workshop, a problem definition was given for which outline solutions were requested. The problem was designed to address a great many issues, for which the solutions given in the general literature would make conflicting assumptions, and thus would not be admissible. Problem areas addressed included algorithm design, temporal behaviour including hard deadlines, limited communication bandwidth, migration of processing due to overload and fault tolerance. The problem was taken from the defense domain and consists of a caricature specification of an air defense system View full abstract»

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  • Integrated scheduling of tasks and messages in distributed real-time systems

    Page(s): 64 - 71
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    The scheduling of tasks in distributed real-time systems has attracted many researchers in the recent past. The distributed real-time system considered here consists of uniprocessor or multiprocessor nodes connected through a multihop network. Scheduling in such a system involves scheduling of dynamically arriving tasks within a node (local scheduling) and migration of tasks across the network (global scheduling) if it is not possible to schedule them locally. Most of the existing schemes on distributed real-time task scheduling ignore the underlying message scheduling required for global scheduling of tasks. These schemes consider the load on the processors at a node as the basis to migrate tasks from a heavily loaded node (sender) to a lightly loaded node (receiver). We believe that the identification of a receiver node should be based not only on the load on its processors, but also on the availability of a lightly loaded path from the sender to that receiver. In this paper we present an integrated framework for distributed real-time dynamic task scheduling (i) by proposing algorithms for transfer location, and information policies which take into account the states of both the processors and the links, and (ii) by proposing interactions among these policies and schedulers so that the guarantee ratio (ratio of number of tasks guaranteed to the number of tasks arrived) is improved as compared to algorithms where only local scheduling is done. For local scheduling, we use a variation of myopic algorithm. The effectiveness of the proposed framework has been evaluated through simulation View full abstract»

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  • Simulation-based performance analysis of distributed systems

    Page(s): 244 - 249
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    Performance analysis of distributed systems may be performed on different levels of abstraction. An accurate but time-consuming method is the construction of a simulation model which includes the different subsystems, the communication system, and the load profile. In particular, this approach seems to be very powerful for real-time systems because of the inherent possibility of precise calculations of delays and processing times. A VHDL-based approach is presented which supports the performance analysis of mixed discrete-continuous distributed systems View full abstract»

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  • OPC the de facto standard for real time communication

    Page(s): 289 - 294
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    The OLE/COM standard (OLE=Object Linking and Embedding, COM=Common Object Model), Microsoft's object technology, integrates applications with a great deal of compatibility between the various applications. For example, a CAD drawing can be integrated into a Word document or an Excel table. Even applications that are programmed in different languages can be integrated. OLE is based on the binary standard COM and communication between different OLE components is possible. OPC (OLE for Process Control) is a communication standard that is based on OLE. It will allow for more efficient and easier communication between the different automation levels. Using the OLE technology, OPC defines methods and objects to achieve communication between the different software applications, no matter if these exist on a PC in the process management environment, or on process control equipment. OPC provides a standard application programming interface for data exchange that can simplify I/O driver development and improve operator interface system performance View full abstract»

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  • A pre-run-time scheduling algorithm for object-based distributed real-time systems

    Page(s): 160 - 167
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    The most important goal in hard real-time systems is to guarantee that all timing constraints are satisfied. Even though object-based techniques (which contain reusable software components) are used to manage the complexity in the software development process of such systems, execution efficiency may have to be sacrificed, due to the large number of procedure calls and contention for accessing software components. These issues are addressed by the following parallelizing techniques: converting potentially inefficient procedure calls to a source of concurrency via asynchronous remote procedure calls (ARPC); and replicating (or cloning) software components to reduce the contention. The existing object-based scheduling algorithms construct an initial schedule and apply incremental parallelization techniques to modify the initial schedule until a feasible schedule is generated. These algorithms are applicable for scheduling only multiple independent tasks. This paper describes a pre-run-time scheduling algorithm for a set of periodic object-based tasks having precedence constraints among them. The algorithm employs parallelism exploitation techniques to guarantee timeliness in almost fully predictable environments such as factory automation, aerospace, and avionics. It allocates the components of object-based periodic tasks to the sites of a distributed system based on a clustering heuristic which takes into account the ARPC parallelism and load balancing, and schedules them on respective sites View full abstract»

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  • Use cases for distributed real-time software architectures

    Page(s): 34 - 42
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    This paper describes how use cases can be applied to the architectural design of distributed real-time applications. In order to benefit from use cases in distributed real-time design it is necessary to extend use cases, particularly in the design phase, when important design decisions need to be made. To achieve this, use cases are integrated with CODARTS (Concurrent Design Approach for Real-Time Systems) distributed design concepts. Three different categories of use cases are described here, client/server use cases, subscription use cases and real-time control use cases. Different forms of message communication are associated with the different use case types. The overall design of the distributed real-time system is achieved by composing it from the use cases View full abstract»

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  • Parallel distributed real-time systems in manufacturing (an aerospace view)

    Page(s): 284 - 288
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    An overview of the evolution of distributed real-time controllers in aerospace manufacturing environments is given. Programmable logic controllers (PLCs) and projected PLC market revenues are reviewed, as well as manufacturing deployment strategies and customer support. The hidden costs of PLC technology are identified. Examples of today's state-of-the-art parallel distributed real-time manufacturing systems are given. Large hidden support costs associated with such systems are identified. In conclusion, ideas on how new real-time distributed systems can be supported by the current corporate philosophy of speed, quality and cost, are discussed. Techniques of how to move forward to the implementation of new real-time distributed systems are presented View full abstract»

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  • Properties of hard real-time tasks for on-line scheduling on multiprocessors

    Page(s): 168 - 176
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    We consider the properties of hard real-time tasks in the context of online scheduling on multiprocessors in an environment where the parameters concerning the set of all future tasks are not known a-priori. We consider a set of ready tasks T0 that need to be scheduled at time 0. We derive a property PT on T0 such that if T0 satisfies this property, any task set Tt, t>0, whose parameters are not known a-priori, can be scheduled successfully online. We also give an online scheduler called MLLA. Further, we show that if a task set does not satisfy the property PT, there exists no online scheduler which can schedule any future task set Tt, t>0 View full abstract»

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  • REALISME: real time integrated software methods adapted to ESA's needs

    Page(s): 201 - 210
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    Space systems development is becoming more and more critical due to the complexity of the industrial organisation, the increase in technical complexity, the criticality of the functions to be supported, and that in a more and more competitive environment. Within these developments, software is playing an increasing and more central role. This leads to new or stronger constraints on the software. Because of this, the European Space Agency (ESA) has already conducted several studies, e.g. HOORA (Hierarchical Object Oriented Analysis), HOOD (Hierarchical Object Oriented Design) and ESSDE (European Space Software Development Environment). This report describes the results of the REALISME project, which aims to propose a consistent approach for real-time software development, integrating the existing (object oriented) methods for analysis and design. The emphasis is on providing clear and ready-to-use guidelines, based on existing methods View full abstract»

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  • Real-time multimedia data processing using VLIW hardware stack processor

    Page(s): 296 - 301
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    We propose the real-time processing of multimedia data using a special purpose processor. We introduce a VLIW architecture and a hardware stack for our multimedia processor. The VLIW-Hardware Stack Processor (VLIW-HSP) consists of four hardware stack units and one control unit. We discuss real-time multimedia data processing using the VLIW architecture. We show the design of VLIW-HSP and present several performance evaluations using a software simulation of VLIW-HSP. The results of these evaluations indicate that the hardware stack typically achieves a 20% speed improvement. We describe a hardware emulator for VLIW-HSP using an Xilinx FPGA which is necessary for application level performance evaluation View full abstract»

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  • TARTOS-tool box for active real-time object-oriented database system models

    Page(s): 131 - 140
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    When real-time databases are to be used in application environments, new requirements should be met by the underlying data model. While the relational data model is very good at modeling simple real-world entities with temporal and logical consistency, its limits are obvious when more modeling power is needed. An object-oriented approach can answer the modeling needs, but on the other hand it can introduce unwanted complexity to a model. One way to overcome these problems is to define a set of independent elements that can be used as the primary components of a model. A model designer can choose suitable components to design a model that is tailored to specific application needs. We call this a tool box approach. We present our tool box approach called TARTOS (Tool box for Active Real-Time Object-oriented database System models). It defines a database model from a set of components that are either necessary or optional to the model. Every component has a structure that is made of a set of necessary and optional subcomponents. With this approach it is possible to design a tailored real-time object-oriented data model that answers exactly the needs presented for a specific environment without extra complexity View full abstract»

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  • Design of a real-time parallel kernel using LOTOS

    Page(s): 177 - 181
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    The main goal of this work is to show how the formal description technique (FDT) Language of Temporal Ordering Specification (LOTOS), a standard of the International Standards Organization (ISO), can be useful in the design of real-time systems. This paper concentrates on the specification phase of a development methodology and uses as an example the parallel real-time kernel RTXC/MP developed by Intelligent Systems International and being nowadays commercialized as Virtuoso by Eonic Systems View full abstract»

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  • MetaH support for real-time multi-processor avionics

    Page(s): 11 - 21
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    MetaH is a language for describing the software and hardware architecture of real-time fault-tolerant securely partitioned avionics systems. The MetaH toolset supports, among other things, real-time schedulability analysis and the automatic generation of “glue” code that implements real-time message passing and process dispatching for a class of multi-processor target architectures. We describe the development methodology and typical requirements that motivated the language and tools. We give an overview of the message and process scheduling methods used in the current toolset and briefly discuss research to extend this approach to larger-scale distributed systems such as fire control and air traffic control View full abstract»

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  • Automatic derivation of path and loop annotations in object-oriented real-time programs

    Page(s): 257 - 262
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    This paper presents a new method, based on the notion of abstract interpretation, that can be used to derive path and loop annotations automatically for object-oriented real-time programs. Normally these annotations, necessary for the correct calculation of the worst case execution time (WCET), must be given manually by the programmer. The method is illustrated by the analysis of an example in Smalltalk View full abstract»

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  • Coming attractions in software architecture

    Page(s): 2 - 9
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    Software architecture has emerged as an important topic in software engineering. This paper examines what is new about the subject, and what is not, and what research trends we may expect in the future. We discuss the promise that work in the field holds, and organize the work into five predominant themes: selection, representation, evaluation, development, and recovery. Technology for the formal representation of architectures is examined in detail, along with notions of architectural styles and patterns. The paper begins by examining the range of meanings associated with the term in order to provide a context for its treatment View full abstract»

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  • Toward a scalable design for command and control systems

    Page(s): 43 - 52
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    Command and control systems exist in a world of constantly shifting demands and expectations; therefore, producing scalable, evolvable systems has always been a priority of system designers. However the need to meet performance requirements has often been a restraint on scalability goals. Advances in the speed and capacity of computational and communications equipment have substantially increased the range of scalability that can be achieved while still meeting performance requirements. The High Performance Distributed Computing Program (HiPer-D) has demonstrated a design for the AEGIS weapons system, which is close to achieving the full range of operational requirements while providing scalability along several dimensions. This paper discusses the HiPer-D design, its context, development, and efforts to achieve system level performance View full abstract»

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  • Synchronization for distributed real-time applications

    Page(s): 81 - 90
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    Several distributed applications are characterized by real-time constraints on response times. High-level actions in such distributed applications are modeled by nonatomic events which are collections of atomic events. This paper studies synchronization relations between nonatomic events in such distributed real-time application executions. The relations form a fine-grained hierarchy that can be used to select suitable relations with good properties and clear intuitions, depending on the application. We show the use of the proposed relations in specifying solutions for distributed mutual exclusion and in specifying distributed predicates. As an example of an application, we show how a real-time air defence system that needs to enforce distributed mutual exclusion and specify and evaluate distributed predicates can use the proposed relations View full abstract»

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  • Real-time scheduling in video systems

    Page(s): 309 - 318
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    We consider the problem of mapping video algorithms onto systems of high-performance video signal processors with hard real-time constraints. The mapping problem under consideration is computationally hard due to the many constraints that need to be satisfied. We present a compact mathematical formulation which identifies the decision variables and the constraints that are involved. We demonstrate that the mapping problem is NP-hard in the strong sense. The insight resulting from the mathematical formulation leads to a solution approach in which the problem is decomposed into subproblems called delay management, partitioning, and scheduling. These subproblems are handled with well-known techniques from the literature such as network flow, local search, and constraint satisfaction View full abstract»

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  • Multiple node-disjoint path protocol for virtual paths in ATM networks

    Page(s): 91 - 97
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    This paper presents a routing protocol for finding multiple node-disjoint paths between two nodes in a computer network. Finding the maximal number of node-disjoint paths is one of the most important themes in ATM networks to increase the level of network reliability. In ATM networks, the virtual path (VP) concept is appropriate to network control for failure restoration (path restoration). In the VP concept, the path restoration is realized rapidly by rerouting failed paths to their backup node-disjoint paths. Some multiple path protocols have been proposed to enhance reliability or throughput. However, such multiple paths are shared with each other in some nodes or channels. Only node-disjoint path protocols enable the most reliable real-time routing in ATM networks. In the proposed protocol, each node in the network has the same procedure, which is driven by local information with respect to the network topology such as an adjacent node on a spanning tree in the network. Therefore, the execution of the protocol can continue after changes of the network topology View full abstract»

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