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Real-Time Technology and Applications Symposium, 1996. Proceedings., 1996 IEEE

Date 10-12 June 1996

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  • 1996 IEEE Real-Time Technology and Applications Symposium Proceedings

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    Freely Available from IEEE
  • On ATM support for distributed real-time applications

    Page(s): 70 - 78
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    Considers the problem of applying ATM technology in designing distributed industrial plant control applications with integrated real-time communication requirements. In particular, we first examine (1) the design space using current ATM service categories and their corresponding traffic models, and (2) the mathematical and practical implications of the traffic models. We then present a taxonomy of the algorithms available to implement the service categories that can provide performance guarantees. Through the examination, we shed light on the gap between what is usually assumed in research and what the actual ATM network will provide. We then show how real-time communication can be mapped onto ATM service categories and demonstrate the limitations of ATM services. Finally, we describe the concept of user-level multiplexing as a means to overcome the limitations. View full abstract»

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  • Author index

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  • A semantic-based concurrency control protocol for real-time transactions

    Page(s): 59 - 67
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    Real-time database systems must maintain both logical and temporal data integrity so that transactions can respond to real-world events timely and predictably. For real-time applications, such as avionics and process control, that are connected to sensor devices, the consistency between the device readings and the current values used by transactions could be more important than the serializability of transactions. In this paper, we propose a semantic-based concurrency control protocol that increases the responsiveness of transactions. A method compatibility matrix is created for each object in the database. Transactions request different types of methods according to their consistency requirements. We show the performance of the semantic-based concurrency control protocol by simulation View full abstract»

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  • Mechanical verification of timed automata: a case study

    Page(s): 192 - 203
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    The paper reports the results of a case study on the feasibility of developing and applying mechanical methods, based on the proof system PVS, to prove propositions about real time systems specified in the Lynch-Vaandrager timed automata model. In using automated provers to prove propositions about systems described by a specific mathematical model, both the proofs and the proof process can be simplified by exploiting the spectral properties of the mathematical model. The paper presents the PVS specification of three theories that underlie the timed automata model, a template for specifying timed automata models in PVS and an example of its instantiation, and both hand proofs and the corresponding PVS proofs of two propositions. It concludes with a discussion of our experience in applying PVS to specify and reason about real time systems modeled as timed automata View full abstract»

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  • Supporting predictability in real-time database systems

    Page(s): 38 - 48
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    Real-time database systems (RTDBSs) have timing constraints in their specifications, such as read times, deadlines and other temporal constraints. In addition, RTDBSs must adapt to changes in the operating environment and guarantee the completion of critical transactions. Previous research efforts in RTDBSs have been focused on scheduling transactions with soft or firm deadlines with serializability as the sole correctness criterion. Few results have been reported for supporting predictable transaction execution and guaranteeing the temporal consistency of data. The goal has been to minimize the deadline miss ratio and to maintain the logical consistency of data. In this paper, we address the issues of predictability and temporal consistency in RTDBSs. We briefly discuss the characteristics and requirements of RTDBSs, and present a transaction processing scheme that supports multiple levels of predictability for real-time transactions. The performance of the proposed scheme and the cost of achieving a high level of predictability is studied by using simulation View full abstract»

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  • The design of an open system with distributed real-time requirements

    Page(s): 82 - 90
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    This paper describes some of the US Navy's New Attack Submarine C3I system-an open system with distributed real-time requirements. It also presents our research design and prototyping efforts that address these requirements. It concludes by discussing several areas where further research is needed to allow open systems to better support real-time applications View full abstract»

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  • Tutorial: real-time object-oriented modeling (ROOM)

    Page(s): 214 - 217
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    Developing real time software is particularly challenging since the complexity of the physical world has to be accommodated as well as stringent resource and timeliness constraints. Such circumstances require special language support over and above what can be found in general purpose programming languages. ROOM is both an object oriented modeling language and a development method specifically designed for dealing with large real time systems. It supports automatic code generation to ensure reliability and increase productivity View full abstract»

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  • A flexible tool kit for the development of real-time applications

    Page(s): 260 - 262
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    When developing hard real time applications, one of the crucial aims of the designer(s) is to ensure a predictable time behaviour in all anticipated conditions. In particular, it would be highly desirable to verify the compliance of the application with its timing requirements in the early steps of the development, especially at the design stage; an early detection of performance bottlenecks, critical resource usage or critical timing paths is vital to properly design the allocation of the computing and the interactions among the program modules. The toolkit presented facilitates the development of complex hard real time applications and allows the user to describe the application requirements according to three hierarchical levels: the application level, the node level, and the task level. With respect to other approaches proposed in the literature (like PERTS (J.W.S. Lin et al., 1993) or IPTES (G. Leon et al., 1993)), our design cycle is based on an extended spiral metamodel in which the real time scheduling support is considered from the beginning of the design process. An advantage of this approach is to drastically reduce the number of trial and error iterations, by examining the non functional requirements of the applications in the early design phases View full abstract»

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  • AIDA-based real-time fault-tolerant broadcast disks

    Page(s): 49 - 58
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    The proliferation of mobile computers and wireless networks requires the design of future distributed real-time applications to recognize and deal with the significant asymmetry between downstream and upstream communication capacities, and the significant disparity between server and client storage capacities. Zdonik et al. (1994) have proposed the use of broadcast disks as a scalable mechanism to deal with this problem. In this paper, we propose a new broadcast disks protocol, based on our Adaptive Information Dispersal Algorithm (AIDA). Our protocol is different from previous ones in that it improves both timeliness and fault tolerance, while allowing for a finer control of multiplexing of prioritized data. We start with a general introduction to broadcast disks. Next, we propose broadcast disk organizations that are suitable for real-time applications. Next, we present AIDA and show its fault-tolerance properties. We conclude with the description and analysis of AIDA-based broadcast disk organizations that achieve both timeliness and fault-tolerance, while preserving downstream communication capacity View full abstract»

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  • Efficient worst case timing analysis of data caching

    Page(s): 230 - 240
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    Recent progress in worst case timing analysis of programs has made it possible to perform accurate timing analysis of pipelined execution and instruction caching. However there has not been much progress in worst case timing analysis of data caching. This is mainly due to load/store instructions that reference multiple memory locations such as those used to implement array and pointer based references. These load/store instructions are called dynamic load/store instructions and most current analysis techniques take a very conservative approach to their timing analysis. In many cases, it is assumed that each of the references from a dynamic load/store instruction will miss in the cache and replace a cache block that would otherwise lead to a cache hit. This conservative approach results in severe overestimation of the worst case execution time (WCET). The paper proposes two techniques to minimize the WCET overestimation due to such load/store instructions. The first technique uses a global data flow analysis technique to reduce the number of load/store instructions that are misclassified as dynamic load/store instructions. The second technique utilizes data dependence analysis to minimize the adverse impact of dynamic load/store instructions. The paper also compares the WCET bounds of simple benchmark programs that are predicted with and without applying the proposed techniques. The results show that they significantly (up to 20%) improve the accuracy of WCET estimation especially for programs with a large number of references from dynamic load/store instructions View full abstract»

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  • A framework for simulation of concurrency control policy in real-time systems

    Page(s): 91 - 99
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    Control of concurrency is a critical aspect of both performance and correctness of real-time systems. Use of formal policies and mechanisms for concurrency control, in the style of transaction processing systems, would make it easier to reason about the logical correctness of concurrently executing processes in real-time systems. Adaptation of transaction processing techniques to real-time environments is a goal of our research. In this paper we describe a simulator used to study the interactions among scheduling policy, overload management, and concurrency control policy and the effects on the performance of real-time applications. The structure and capabilities of the simulator are described and its use in the evaluation of some concurrency control options for a real-time application is demonstrated. Through this example, we show how the simulation is customized for different processing models, scheduling options, and concurrency control policies View full abstract»

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  • A robotic assembly application on the Spring real-time system

    Page(s): 19 - 28
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    The Spring real-time system and environment provides methods for program representation and corresponding run-time system support that allow programs to meet the predictability demands of complex real-time applications. The primary objective of the work described in this paper is to present the experiences gained and the lessons learned from porting a real-world, real-time application to make it predictable and flexible. The exercise has also provided a test case which helps to answer questions about the completeness and ease of use of software development tools that have been developed to provide for flexibility while achieving real-time guarantees. This test case is derived from an existing real-time application in industry-a robotic work-cell that is currently in use for the assembly of circuit boards. From our experience with this reengineering exercise, we believe that a user must possess a good understanding of the following: (1) the general properties of the target hardware-for effective process and resource layout, and (2) the shared resource usage and interprocess communication, and, more generally, the statements that cause processes to suspend-for efficient run-time representation of the tasks. Tools that help the user obtain this understanding and perform detailed timing analysis are essential. Although the algorithms and tools used in the reimplementation were developed in the context of the Spring real-time environment, we believe that the lessons learned from this experiment will be useful not only to potential users of Spring, but also to real-time practitioners at large View full abstract»

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  • Building real-time music tools visually with Sonnet

    Page(s): 11 - 18
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    We are building a variety of interactive music tools using Sonnet, a visual programming language in use at our center. Originally designed for sonification experiments for monitoring and debugging programs, Sonnet has grown into a more general system with a focus on real-time event-driven applications. In this paper, we describe some of the features of Sonnet followed by some examples of how it is being used View full abstract»

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  • CAISARTS: a tool for real-time scheduling assistance

    Page(s): 150 - 159
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    CAISARTS (Conceptual, Analytical, and Implementation Scheduling Advice for Real-Time Systems) is a rule-based system used by real-time application designers to obtain expert assistance for all aspects of the design related to scheduling: granularity of tasks, allocation of tasks, choice and analysis of scheduling paradigm, analysis of overheads of particular operating systems and scheduling paradigms, and code templates for tasks. The rule base is partitioned; subsets of the rule base can be selected for firing, thus enabling the user to ask CAISARTS for advice and analysis relevant for different phases of the design. In contrast to existing real-time tools, CAISARTS attempts to cover the entire design process related to scheduling without focusing on, for example, solely schedulability analysis. A unique feature of CAISARTS is that its rule base is extensible by the user-a graphical interface is used to add new rules as new real-time results are identified. Challenges in the design of the initial rule set include how to design and partition the rule base so that it can be both easily modifiable and readily usable by the user in choosing rules to fire; how to encode rules that are inherently contradictory; how to encode ambiguous knowledge; and how to make the rules both comprehensive and precise. The effectiveness of CAISARTS is shown through its use on a representative distributed real-time system scenario with end-to-end constraints View full abstract»

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  • Evaluation of wireless soft real-time protocols

    Page(s): 139 - 146
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    Communication between current military real-time systems and future interconnection of general purpose, embedded real-time systems will often require wireless communications. However, there has been little work undertaken to offer support for real-time applications on wireless networks. We present and evaluate three protocols; variations of two published protocols by Paterakis and Gallager as well as our new one, the Sliding Partition (SP) collision resolution algorithm (CRA). In a real-time setting, the modified Gallager CRA consistently performs worst of the three we consider. We observe that when the deadline range is small, the Sliding Partition CRA performs best. When the deadline range is large, however, the Paterakis CRA performs slightly better than the SP CRA. Both analytic and simulation results are obtained to study the maximum input traffic rates that can be sustained for various laxities, delay bounds, and message loss rates View full abstract»

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  • Adding instruction cache effect to schedulability analysis of preemptive real-time systems

    Page(s): 204 - 212
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    Cache memories are commonly avoided in real time systems because of their unpredictable behavior. Recently, some research has been done to obtain tighter bounds on the worst case execution time (WCET) of cached programs. These techniques usually assume a non preemptive underlying system. However, some techniques can be applied to allow the use of caches in preemptive systems. The paper describes how to incorporate the effect of instruction cache to the Response Time schedulability Analysis (RTA). RTA is an efficient analysis for preemptive fixed priority schedulers. We also compare through simulations the results of such an approach to both cache partitioning (increase of the cache predictability by assigning private cache partitions to tasks) and CRMA (Cached RMA: cache effect is incorporated in the utilization based rate monotonic schedulability analysis). The results show that the cached version of RTA (CRTA) clearly outperforms CRMA, however the partitioning scheme may be better depending on the system configuration. The obtained results bound the applicability domain for each method for a variety of hardware and workload configurations. The results can be used as design guidelines View full abstract»

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  • Scalable compositional reachability analysis of real-time concurrent systems

    Page(s): 182 - 191
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    A description model for high level behavior of a real time concurrent system is presented. A verification algorithm is then devised to take advantage of interaction locality and symmetry and internal operation concealment in the model. A system called VERIFAST implements the algorithm. Experiments show that VERIFAST runs fast and exhibits time complexity linear to the size of concurrency in a benchmark View full abstract»

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  • Putting fixed priority scheduling theory into engineering practice for safety critical applications

    Page(s): 2 - 10
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    Describes the approach proposed by the York University Technology Centre for introducing fixed-priority scheduling into industrial safety-critical hard real-time systems. The work has been performed within the context of a class A (safety-critical) system as defined by civil aircraft software standard DO178B. Traditionally, class A systems have been scheduled by a cyclic executive. However, many such systems can be re-designed using a fixed-priority scheduler. This saves time and money, with no significant increase in risk. Also, significant technical benefits are apparent. This paper describes the timing requirements of the system, provides a potential scheduling approach (including appropriate timing analysis), and outlines an approach for gathering the necessary evidence for presentation to certification authorities View full abstract»

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  • Predictable communication protocol processing in real-time Mach

    Page(s): 220 - 229
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    Scheduling of many different kinds of activities takes place in distributed real time and multimedia systems. It includes scheduling of computations, window services, filesystem management, I/O services and communication protocol processing. We investigate the problem of scheduling communication protocol processing in real time systems. Communication protocol processing takes a relatively substantial amount of time and if not structured correctly, unpredictable priority inversion and undesirable timing behavior can result to applications communicating with other processors but are otherwise scheduled correctly. We describe the protocol processing architecture in the RT-Mach operating system, which allows the timing of protocol processing to be under strict application control. An added benefit is also obtained in the form of higher performance. This scheduling architecture is consistent with the: other RT-Mach scheduling mechanisms including fixed priority scheduling and processor reservation. The benefits of this protocol architecture are demonstrated both under synthetic workloads and in a realistic distributed videoconferencing system we have implemented in RT-Mach. End to end delays for both audio and video are as predicted even with other threads competing for the CPU and the network View full abstract»

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  • RTCAST: lightweight multicast for real-time process groups

    Page(s): 250 - 259
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    We propose a lightweight fault tolerant multicast and membership service for real time process groups which may exchange periodic and aperiodic messages. The service supports bounded time message transport, atomicity, and order for multicasts within a group of communicating processes in the presence of processor crashes and communication failures. It guarantees agreement on membership among the communicating processors, and ensures that membership changes (e.g., resulting from processor joins or departures) are atomic and ordered with respect to multicast messages. We provide the flexibility of an event triggered approach with the fast message delivery time of time triggered protocols, such as TTP (H. Kopetz and G. Grunstidl, 1994), where messages are delivered to the application immediately upon reception. This is achieved without compromising agreement order and atomicity properties. In addition to the design and details of the algorithm, we describe our implementation of the protocol using the x-Kernel protocol architecture running on RT Mach 3.0 View full abstract»

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  • Supporting the specification and analysis of timing constraints

    Page(s): 170 - 178
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    Real-time programmers have to deal with the problem of relating timing constraints associated with source code to sequences of machine instructions. This paper describes an environment to assist users in the specification and analysis of timing constraints. A user is allowed specify timing constraints within the source code of a C program. A user interface for a timing analyzer was developed to depict whether these constraints were violated or met. In addition, the interface allows portions of programs to be quickly selected with the corresponding bounded times, source code lines, and machine instructions automatically displayed The result is a user-friendly environment that supports the user specification and analysis of timing constraints at a high (source code) level and retains the accuracy of low (machine code) level analysis View full abstract»

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  • EMERALDS: a microkernel for embedded real-time systems

    Page(s): 241 - 249
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    EMERALDS (Extensible Microkernel for Embedded Real Time Distributed Systems) is a real time microkernel designed for cost conscious small to medium size embedded systems. It not only offers standard OS services like multi threaded processes, real time scheduling, protected address spaces, message passing, semaphores, and timers, but does so in an efficient manner while keeping the kernel size to just tens of kilobytes. For efficiency, EMERALDS uses the novel approach of mapping the kernel into each user level address space, so even with full memory protection, system calls do not need context switches unless a user level server is involved. EMERALDS also provides the flexibility for users to add communication protocol stacks and device drivers as user level servers without modifying the kernel. We have completed a uniprocessor version of EMERALDS for the Motorola 68040 processor whose size is under 13 KBytes. Context switch takes under 12 μs and system calls have overhead just 1.8 μs more than that of simple subroutine calls View full abstract»

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  • DRTSS: a simulation framework for complex real-time systems

    Page(s): 160 - 169
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    This paper describes a simulation framework called DRTSS, which allows its users to easily construct discrete-event simulators of complex, multi-paradigm, distributed real-time systems. Preliminary, high-level system designs can be entered into DRTSS to gain initial insight into the timing feasibility of the system. Later, detailed hierarchical designs can be evaluated and more detailed analysis can be undertaken. DRTSS is a member of the PERTS family of timing-oriented prototyping and verification tools [17]. It complements the PERTS schedulability analyzer tool by dealing with complex real-lime systems for which a priori schedulability analysis is difficult or impossible View full abstract»

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  • Providing message delivery guarantees in pipelined flit-buffered multiprocessor networks

    Page(s): 120 - 129
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    Real-time applications when mapped to distributed memory multiprocessors produce periodic messages with an associated deadline and priority. Real-time extensions to wormhole routing (WR) with multiple virtual channels (VCs), suffer from unbounded priority inversion, rendering the global priority order ineffective. We propose a new flow control mechanism called Preemptive Pipelined Circuit Switching for Real-Time messages (PPCS-RT). To bound the priority inversion, we extend the model to PPCS-RTph, with preemption history stack for each VC. For the PPCS-RTph model, we describe a simple feasibility test and validate the test through flit level simulations. To improve the percentage of feasible messages, and average link utilization of the feasible message set, we also evaluate an enhanced PPCS-RTph model with additional architectural features View full abstract»

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