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real-time Systems Symposium (RTSS)

作者： C.-J. Hou K.G. Shin Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

The authors address the problem of allocating (assigning and scheduling) periodic task modules to processing nodes (PNs) in distributed real-time systems subject to task precedence and timing constraints. Using the branch-and-bound technique, a module allocation algorithm (MAA) is proposed to find an optimal allocation that maximizes the probability of meeting task deadlines. To incorporate both timing and logical correctness into module allocation, the probability of meeting task deadlines is used as the objective function. The MAA is then applied to find an optimal allocation of task modules in a distributed system. The timing aspects embedded in the objective function drive the MAA not only to assign task modules to PNs, but also to use a module scheduling algorithm for scheduling all modules assigned to each PN so that all tasks may be completed in time. Several numerical examples are presented to demonstrate the effectiveness and practicality of the proposed algorithms.< >

关键词： real time systems Timing Distributed computing Processor scheduling Laboratories Flow graphs Scheduling algorithm Polynomials Load management Hazards

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Derivation of Hard Deadlines for real-time Control Systems

Derivation of Hard Deadlines for Real-Time Control Systems

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American Control Conference (ACC)

作者： Kang G. Shin Hagbae Kim Department of Electrical Engineering and Computer Science Real-Time Computing Laboratory University of Michigan Ann Arbor MI USA

The computation-time delay in the feedback controller of a real-time control system may cause failure to update the control input during one or more sampling periods. A dynamic failure is said to occur if this delay exceeds a certain limit called a hard deadline. We present a method for calculating the hard deadlines in linear time-invariant control systems. To derive necessary conditions for (asymptotic) system stability, the state difference equation is modified based on an assumed maximum delay and the probability distribution of delays whose magnitudes are less than, or equal to, the assumed maximum delay. Moreover, the allowed state-space - which is derived from given input and state constraints - is used to calculate the hard deadline as a function of time and the system state. We also consider a one-shot delay model in which a single event causes a dynamic failure.

关键词： real time systems Control systems Delay effects Electric variables control Electromagnetic interference computer aided instruction Linear feedback control systems Sampling methods Difference equations Probability distribution

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Fault-tolerant real-time communication in distributed computing systems

Fault-tolerant real-time communication in distributed comput...

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International Symposium on Fault-Tolerant computing (FTCS)

作者： Q. Zheng K.G. Shin Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

An increasing number of applications require packets to be delivered reliably within prespecified delay bounds. It is shown how this can be achieved by using real-time channels that make soft reservation of network resources to ensure the timely delivery of real-time packets. Algorithms are presented for the establishment of real-time channels, and it is shown how the basic real-time channels can be enhanced to be fault tolerant using the multiple paths between a pair of communicating nodes. The contribution of the former is a tighter schedulability condition that makes more efficient use of network resources than other existing approaches, and the contribution of the latter is a significant improvement in fault tolerance over the basic real-time channel, which is inherently susceptible to component failures.< >

关键词： Fault tolerant systems real time systems Distributed computing Circuits Bandwidth Delay Fault tolerance Asynchronous transfer mode Intelligent networks computer networks

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real-time communication in local area ring networks

Real-time communication in local area ring networks

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Conference on Local computer Networks (LCN)

作者： Q. Zheng K.G. Shin Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

The feasibility of using buffered transmission, which has the advantages of eliminating the token passing overhead and relieving the network interface from the complex token handling operations, is considered. The concept of a real-time channel (RTC) and the RTC establishment procedures are reviewed. Its performance is then compared with the FDDI timed token protocol. Simulation results show that the buffered transmission in local area ring networks equipped with real-time channels enhances both the networks' throughput and the ability to support heterogeneous real-time traffic. The implementation of the network interface is also examined with an example design showing the feasibility of real-time channels in high-speed local area networks.< >

关键词： Intelligent networks FDDI Throughput Access protocols Local area networks Network topology Token networks Delay effects Media Access Protocol Network interfaces

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Design and evaluation of real-time communication for FieldBus based manufacturing systems

Design and evaluation of real-time communication for FieldBu...

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Conference on Local computer Networks (LCN)

作者： K.G. Shin C.-C. Chou Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

A strategy for handling real-time communications under the FieldBus protocol, which provides end-to-end delivery delay guarantees for time-critical messages, is proposed. This strategy provides a fast local mechanism for establishing intraworkcell real-time connections, while supporting global interworkcell real-time connections. The proposed strategy is fully compatible with the current draft proposal of the FieldBus protocol and also provides flexibility for the choice of scheduling algorithms and adaptability for different traffic loads. Numerical examples are given based on a typical manufacturing network.< >

关键词： real time systems Field buses Manufacturing systems Protocols Delay Manufacturing processes Process control time factors Job shop scheduling computer network management

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Communication-oriented assignment of task modules in hypercubic multicomputers

Communication-oriented assignment of task modules in hypercu...

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International Conference on Distributed computing Systems

作者： B.-R. Tsai K.G. Shin Real-Time Computing Laboratory Computer Science and Engineering Division Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

The problem of mapping a task that is composed of interacting modules onto a hypercube multicomputer is formulated and solved by minimizing an objective function called the communication traffic. The objective function allows module assignments to be found with the usual straightforward combinatorial optimization techniques. The problem of finding an assignment that minimizes the communication traffic is proved to be NP-hard, so a standard state-space search algorithm as well as other heuristic algorithms are used to find optimal/suboptimal solutions. The relative performances of various algorithms are evaluated using simulations. The assignments obtained from these algorithms are evaluated using an event-driven simulator to learn how they perform in real-world execution environments.< >

关键词： Hypercubes Costs Timing Performance evaluation Laboratories computer science Parallel processing Fault tolerance Computational efficiency time measurement

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Enabling Efficient Schedulability Analysis through Program Transformations and Restricted Resource Contention

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IFAC Proceedings Volumes 1992年第11期25卷 269-273页

作者： Alexander D. Stoyenko Thomas J. Marlowe Wolfgang A. Halang Real-Time Computing Laboratory Computer and Information Science New Jersey Institute of Technology Newark New Jersey 07102 USA Mathematics and Computer Science Seton Hall University South Orange New Jersey 07079 USA Computing Science University of Groningen P.O. Box 800 9700 AV Groningen The Netherlands

We present polynomial-time static semantics-preserving transformations of real-time programs. Used in conjunction with schedulability analysis, the transformations significantly increase the class of real-time programs that may be analyzed efficiently for guaranteed schedulability at compile-time. In cases where the form of resource contention among processes resists efficient transformation, we apply a heuristic transformation (and a consequent run-time scheduling heuristic) to allow the programs to be analyzed efficiently.

关键词： real time computer systems schedulability analysis software tools programming languages deterministic analysis performance bounds compilers parallel processing load modeling programming support

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SCHEDULING JOB OPERATIONS IN AN AUTOMATIC ASSEMBLY LINE

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IEEE TRANSACTIONS ON ROBOTICS AND AUTOMATION 1991年第3期7卷 333-341页

作者： SHIN, KG ZHENG, Q Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

This paper addresses the problem of scheduling job operations in an automatic assembly line used for manufacturing a small to medium volume of mixed workparts. The assembly line model used here differs from the classical flow shop model in the following three aspects: 1) there are no buffers at machine stations, 2) constraints associated with the material transport system are included, and 3) for each batch of production, workparts are distinguished in groups, rather than individually. An "optimal" algorithm that requires very little computation is derived first by minimizing the total finish time for two machine assembly lines. This result is then generalized to the problem of scheduling an assembly line with m > 2 machines processing single-operation jobs. In order to reduce the computational complexity of the latter problem, heuristic algorithms are also proposed and shown to work quite well for all the cases considered. Finally, a heuristic solution to the problem of scheduling an assembly line with m > 2 machines processing multioperation jobs is discussed.

关键词： Job shop scheduling Processor scheduling Heuristic algorithms Flexible manufacturing systems Optimal scheduling Assembly systems Manufacturing automation Pulp manufacturing Scheduling algorithm Mass production

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real-time COMMUNICATIONS IN A computer-CONTROLLED WORKCELL

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IEEE TRANSACTIONS ON ROBOTICS AND AUTOMATION 1991年第1期7卷 105-113页

作者： SHIN, KG Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

A computer-integrated manufacturing (CIM) system is composed of several workcells, each of which contains robots, NC machines, sensors, and a transport mechanism. Each CIM workcell is controlled by multiple processors interconnected by an intracell bus, but the individual cells are interconnected by an arbitrary network. This paper considers a communication subsystem that is designed to support real-time control and coordination of devices in each CIM cell. The concept of a poll number is proposed to control the access to the intracell bus. The bus access mechanism with the poll number is intended to minimize the probability of real-time messages missing their deadlines. When a CIM task generates a time-constrained message, a poll number is computed for this message according to the message's deadline and the task's prority. When the intracell bus is free, the various tasks at a workcell that desire to use the bus write the poll number onto the bus and read it back, one bit at a time, starting from the most significant bit. If at any time the bit read back is different from the bit written, then the corresponding task drops out of the contention for the bus. Use of a poll number provides not only for decentralized control of the intracell bus, but also a high degree of flexibility in scheduling messages. The performance of the bus access mechanism with a poll number is analyzed and compared with that of a token bus, which is widely used in CIM systems such as MAP networks. The probability of a real-time message missing its deadline in a token bus is found to be much higher than that of the proposed mechanism.

关键词： computer integrated manufacturing Communication system control Robot sensing systems Robot kinematics Sensor systems Distributed control Job shop scheduling Performance analysis Manufacturing automation Access protocols

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INTELLIGENT COORDINATION OF MULTIPLE SYSTEMS WITH NEURAL NETWORKS

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IEEE TRANSACTIONS ON SYSTEMS MAN AND CYBERNETICS 1991年第6期21卷 1488-1497页

作者： CUI, XZ SHIN, KG Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

Many control applications require cooperation of two or more independently designed, separately located, but mutually affecting, subsystems. In addition to the good behavior of each subsystem, effective coordination of these subsystems is very important to achieve the desired overall system performance. However, such coordination is very difficult to accomplish due mainly to the lack of precise system models and/or dynamic parameters as well as the lack of efficient tools for system analysis, design, and real-time computation of optimal solutions. A new multiple-system coordinator that combines the techniques of intelligent control and neural networks, and forms the high-level coordinator in a hierarchical structure, is proposed. The basic idea is to estimate the effects of the control commands to subsystems using a predictor and modify these commands using a knowledge-based coordinator so as to achieve the desired performance. The predictor is designed for multiple-input, multiple-output systems using neural networks. The knowledge-based coordinator is responsible for a goal-oriented search in its knowledge base and the overall system stability. Because the internal structure and parameters of the low level are not affected by using the proposed method, some commercially designed servo controllers for single systems can be coordinated to perform more sophisticated tasks for multiple systems than originally intended.

关键词： Intelligent networks Neural networks Control systems System performance Intelligent control real time systems Humans Intelligent structures Stability Design methodology

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