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Träfflista för sökning "WFRF:(Cervin Anton) srt2:(2000-2004)"

Sökning: WFRF:(Cervin Anton) > (2000-2004)

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1.
  • Bate, Iain, et al. (författare)
  • Establishing Timing Requirements and Control Attributes for Control Loops in Real-Time Systems
  • 2003
  • Ingår i: Proceedings 15th Euromicro Conference on Real-Time Systems, 2003.. - 0769519369 ; , s. 121-128
  • Konferensbidrag (refereegranskat)abstract
    • Advances in scheduling theory have given designers of control systems greater flexibility over their choice of timing requirements. This could lead to systems becoming more responsive and more maintainable. However, experience has shown that engineers find it difficult to exploit these advantages due to the difficulty in determining the “real” timing requirements of systems and therefore the techniques have delivered less benefit than expected. Part of the reason for this is that the models used by engineers when developing systems do not allow for emergent properties such as timing. This paper presents an approach and framework for addressing the problem of identifying an appropriate and valid set of timing requirements and their corresponding control parameters.
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2.
  • Cervin, Anton, et al. (författare)
  • Feedback-Feedforward Scheduling of Control Tasks
  • 2002
  • Ingår i: Real-Time Systems. - 1573-1383. ; 23:1-2, s. 25-53
  • Tidskriftsartikel (refereegranskat)abstract
    • A scheduling architecture for real-time control tasks is proposed. The scheduler uses feedback from execution-time measurements and feedforward from workload changes to adjust the sampling periods of the control tasks so that the combined performance of the controllers is optimized. The performance of each controller is described by a cost function. Based on the solution to the optimal resource allocation problem, explicit solutions are derived for linear and quadratic approximations of the cost functions. It is shown that a linear rescaling of the nominal sampling frequencies is optimal for both of these approximations. An extensive inverted pendulum example is presented, where the performance obtained with open-loop, feedback, combined feedback and feedforward scheduling, and earliest-deadline first scheduling are compared. The performance under earliest-deadline first scheduling is explained by studying the behavior of periodic tasks under overload conditions. It is shown that the average values of the sampling periods equal the nominal periods, rescaled by the processor utilization.
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3.
  • Cervin, Anton, et al. (författare)
  • Feedback Scheduling of Control Tasks
  • 2000
  • Ingår i: Proceedings of the 39th IEEE Conference on Decision and Control, 2000.. - 0780366387 ; 5, s. 4871-4876
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The paper presents a feedback scheduling mechanism in the context of co-design of the scheduler and the control tasks. We are particularly interested in controllers where the execution time may change abruptly between different modes, such as in hybrid controllers. The proposed solution attempts to keep the CPU utilization at a high level, avoid overload, and distribute the computing resources evenly among the tasks. The feedback scheduler is implemented as a periodic or sporadic task that assigns sampling periods to the controllers based on execution-time measurements. The controllers may also communicate feedforward mode-change information to the scheduler. As an example, we consider hybrid control of a set of double-tank processes. The system is evaluated, from both scheduling and control performance perspectives, by co-simulation of controllers, scheduler, and tanks.
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4.
  • Cervin, Anton, et al. (författare)
  • How Does Control Timing Affect Performance?
  • 2003
  • Ingår i: Control Systems Magazine. - 0272-1708. ; 23:3, s. 16-30
  • Tidskriftsartikel (refereegranskat)abstract
    • The article presents two Matlab-based tools for analysis andsimulation of real-time control systems: Jitterbug andTrueTime.Jitterbug allows the user to compute aquadratic performance criterion for a linear control system undervarious timing conditions. The control system is described using anumber of continuous- and discrete-time linear systems. Astochastic timing model with random delays is used to describe theexecution of the system. The tool can also be used to investigateaperiodic controllers, multirate controllers, and jitter-compensatingcontrollers.TrueTime facilitates event-based co-simulation of amultitasking real-time kernel containing controller tasks and thecontinuous dynamics of controlled plants. The simulations capture thetrue, timely behavior of real-time controller tasks and communicationnetworks, and dynamic control and scheduling strategies can beevaluated from a control performance perspective. The controllers canbe implemented as Matlab functions, C functions, or ordinarydiscrete-time Simulink blocks.A number of examples that illustrate the use of the tools are given.
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5.
  • Cervin, Anton (författare)
  • Integrated Control and Real-Time Scheduling
  • 2003
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The topic of the thesis is codesign of flexible real-time control systems. Integrating control theory and real-time scheduling theory, it is possible to achieve higher resource utilization and better control performance. The integration requires new tools for analysis, design, and implementation. The problem of scheduling the individual parts of a control algorithm is studied. It is shown how subtask scheduling can reduce the input-output latency in a set of control tasks. Deadline assignment under different scheduling policies is considered. A feedback scheduling architecture for control tasks is introduced. The scheduler uses feedback from execution-time measurements and feedforward from workload changes to adjust the sampling periods of a set of control tasks so that the combined performance of the controllers is optimized. The Control Server, a novel computational model for real-time control tasks, is presented. The model combines time-triggered I/O with dynamic, reservation-based task scheduling. The model provides short input-output latencies and minimal jitter for the controllers. It also allows control tasks to be treated as scalable real-time components with predictable performance. Two MATLAB-based toolboxes for analysis and simulation of real-time control systems have been developed. The Jitterbug toolbox evaluates a quadratic cost function for a linear control system with timing variations. The tool makes it possible to investigate the impact of delay, jitter, lost samples, etc., on control performance. The TrueTime toolbox facilitates detailed cosimulation of distributed real-time control systems. The scheduling and execution of control tasks is simulated in parallel with the network communication and the continuous process dynamics.
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6.
  • Cervin, Anton, et al. (författare)
  • Jitterbug and TrueTime: Analysis Tools for Real-Time Control Systems
  • 2002
  • Konferensbidrag (refereegranskat)abstract
    • The paper presents two recently developed, Matlab-based analysis tools for realtime control systems. The first tool, called Jitterbug, is used to compute a performance criterion for a control loop under various timing conditions. The tool makes it easy to quickly judge how sensitive a controller is to implementation effects such as slow sampling, delays, jitter, etc. The second tool, called TrueTime, allows detailed co-simulation of process dynamics, control task execution, and network communication in a distributed real-time control system. Arbitrary scheduling policies may be used, and the tasks may be written in C code, Matlab code, or implemented as Simulink block diagrams.
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7.
  • Cervin, Anton, et al. (författare)
  • Jitterbug - Reference Manual
  • 2003
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • The manual describes the use of Jitterbug, a Matlab toolbox for analysis of real-time control performance. The tool facilitates the computation of a quadratic performance index for a linear control system under various timing conditions.
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8.
  • Cervin, Anton (författare)
  • Merging Real-Time and Control Theory for Improving the Performance of Embedded Control Systems
  • 2004
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • This report describes the work carried out within the research project ``Merging Real-Time and Control Theory for Improving the Performance of Embedded Control Systems''. The overall objective of the work has been to develop integrated control and scheduling methods for improving the performance of real-time control systems with limited resources. The work has fallen into three categories. First, overrun methods for control tasks has been investigated. Specifically, a reservation-based scheduling concept called the Control Server has been further developed, and control experiments on a ball-and-place process have been performed. Second, the issue of jitter in real-time control systems has been explored. The concept of Jitter Margin has been introduced as a link between control stability theory and scheduling theory. In this context, best-case response-time analysis under earliest-deadline-first scheduling has been researched. Third, some development work on the S.Ha.R.K. real-time kernel has been performed. The rate-monotonic and earliest-deadline-first scheduling modules have been extended, and new modules for the elastic task model and the control server model have been implemented.
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9.
  • Cervin, Anton, et al. (författare)
  • The Control Server: A Computational Model for Real-Time Control Tasks
  • 2003
  • Ingår i: Proceedings 15th Euromicro Conference on Real-Time Systems, 2003.. - 0769519369 ; , s. 113-120
  • Konferensbidrag (refereegranskat)abstract
    • The paper presents a computational model for real-time controltasks, with the primary goal of simplifying the control andscheduling co-design problem. The model combines time-triggered I/Oand inter-task communication with dynamic, reservation-based taskscheduling. To facilitate short input-output latencies, a task maybe divided into several segments. Jitter is reduced by allowingcommunication only at the beginning and at the end of a segment. Akey property of the model is that both schedulability and controlperformance of a control task will depend on the reservedutilization factor only. This enables controllers to be treated asscalable real-time components. The model has been implemented in areal-time kernel and validated in a real-time control application.
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10.
  • Cervin, Anton, et al. (författare)
  • The Jitter Margin and Its Application in the Design of Real-Time Control Systems
  • 2004
  • Ingår i: Proceedings of the 10th International Conference on Real-Time and Embedded Computing Systems and Applications.
  • Konferensbidrag (refereegranskat)abstract
    • Based on recent advances in control theory, we propose the notion of jitter margin for periodic control tasks. The jitter margin isdefined as a function of the amount of constant delay in the controlloop, and it describes how much additional time-varying delay can betolerated before the loop goes unstable. Combined with schedulingtheory, the jitter margin can be used to guarantee the stability andperformance of the controller in the target system. It can also beused as a tool for assigning meaningful deadlines to control tasks.We discuss the need for best-case response-time analysis in thiscontext, and propose a simple lower bound under EDF scheduling.Finally, a control-scheduling codesign procedure is given, whereperiods are assigned iteratively to yield the same relativeperformance degradation for each control task.
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11.
  • Cervin, Anton (författare)
  • The Real-Time Control Systems Simulator -Reference manual
  • 2000
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • A Matlab / Simulink-based simulator for real-time control systems is described. The simulator facilitates co-simulation of plant dynamics, controller code execution, and real-time scheduling. Three examples are given. The kernel primitives are described in detail.
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12.
  • Cervin, Anton (författare)
  • Towards the Integration of Control and Real-Time Scheduling Design
  • 2000
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The thesis deals with scheduler and controller co-design for real-time control systems. The overall goal is higher resource utilization and better control performance. One goal is to minimize the performance loss due to jitter and control delays. Another goal is to relax the nominal requirements on hard deadlines and fixed worst-case execution times. A third goal is to provide a co-simulation environment for real-time control systems.
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13.
  • Cervin, Anton (författare)
  • Using Jitterbug to Derive Control Loop Timing Requirements
  • 2003
  • Ingår i: Proceedings of CERTS'03 – Co-Design of Embedded Real-Time Systems Workshop.
  • Konferensbidrag (refereegranskat)abstract
    • Linking scheduling attributes to control performance specifications is a difficult problem. This paper discusses how the MATLAB toolbox Jitterbug can be used to derive timing requirements for control loops from various control performance specifications. The resulting timing requirements include specifications on sampling periods, latencies, and jitter. An overview of the Jitterbug approach is given, and limitations of the tool are pointed out. A control design example is given, and, finally, topics where more research is needed are outlined.
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14.
  • Eker, Johan, et al. (författare)
  • Distributed Wireless Control Using Bluetooth
  • 2002
  • Ingår i: New Technologies for Computer Control 2001.
  • Konferensbidrag (refereegranskat)abstract
    • Bluetooth is currently emerging as one of the most promising personal wireless network technologies. It is primarily designed as a cable replacement between for example a cell phone and a PDA. However the price/performance level also makes it a promising technology outside the office. The automation industry is currently showing interest in using Bluetooth for more industrial applications. However the problems with unreliable links and time delays must be explicitly addressed in any wireless control application in order to make safe and fault tolerant. This paper discusses how to design a fault tolerant wireless distributed control system. An example application where an inverted pendulum is controller over a wireless link is presented.
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15.
  • Henriksson, Dan, et al. (författare)
  • Feedback Scheduling of Model Predictive Controllers
  • 2002
  • Ingår i: Proceedings of the 8th IEEE Real-Time and Embedded Technology and Applications Symposium. - 0769517390 ; , s. 207-216
  • Konferensbidrag (refereegranskat)abstract
    • The paper presents some preliminaryresults on dynamic scheduling of model predictive controllers (MPCs).In an MPC, the control signal is obtained by on-line optimization of acost function, and the MPC task may experience very large variationsin execution time from sample to sample. Unique to this application,the cost function offers an explicit, on-line quality-of-servicemeasure for the task. Based on this insight, a feedback schedulingstrategy for multiple MPCs is proposed, where the scheduler allocatesCPU time to the tasks according to the current values of the costfunctions. Since the MPC algorithm is iterative, the feedbackscheduler may also abort a task prematurely to avoid excessiveinput-output latency. A case study is presented, where the newapproach is compared to conventional fixed-priority andearliest-deadline-first scheduling. General problems related to thereal-time implementation of MPCs are also discussed.
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16.
  • Henriksson, Dan, et al. (författare)
  • Multirate Feedback Control Using the TinyRealTime Kernel
  • 2004
  • Ingår i: Computer and Information Sciences - ISCIS 2004 19th International Symposium, Proceedings (Lecture Notes in Computer Science). - Berlin, Heidelberg : Springer Berlin Heidelberg. - 0302-9743 .- 1611-3349. - 9783540235262 ; 3280, s. 855-865
  • Konferensbidrag (refereegranskat)abstract
    • Embedded microcontrollers are often programmed in plain C and lacksupport for multithreading and real-time scheduling. This can makeit very cumbersome to implement multirate feedback controlapplications. We have developed the TinyRealTime kernel forthe Atmel ATmega8L AVR to show that it is feasible to usehigh-precision, deadline-based scheduling even in a tiny 8-bitprocessor with 1 KB of RAM. The kernel is demonstrated in amultirate control application, where six periodic real-time tasks(four control tasks and two PWM tasks) are used to control twoball-and-beam processes.
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17.
  • Henriksson, Dan, et al. (författare)
  • Multirate feedback control using the TinyTealTime kernel
  • 2004
  • Ingår i: Lecture Notes in Computer Science. - 0302-9743. ; 3280, s. 855-865
  • Tidskriftsartikel (refereegranskat)abstract
    • Embedded microcontrollers are often programmed in plain C and lack support for multithreading and real-time scheduling. This can make it very cumbersome to implement multirate feedback control applications. We have developed the TINYREALTIME kernel for the Atmel ATmegaSL AYR to show that it is feasible to use high-precision, deadlinebased scheduling even in a tiny 8-bit processor with 1 KB of RAM. The kernel is demonstrated in a multirate control application, where six periodic real-time tasks (four control tasks and two pulse width modulation tasks) are used to control two ball-and-beam processes.
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18.
  • Henriksson, Dan, et al. (författare)
  • On Dynamic Real-Time Scheduling of Model Predictive Controllers
  • 2002
  • Ingår i: Proceedings of the 41st IEEE Conference on Decision and Control, 2002. - 0191-2216. - 0780375165 ; 2, s. 1325-1330
  • Konferensbidrag (refereegranskat)abstract
    • The paper discusses dynamic real-time scheduling in the context ofmodel predictive control (MPC). Dynamic scheduling in this settingis motivated by the highly varying execution times associated withMPC controllers. Premature termination of the optimization algorithmis exploited to trade off prolonged computations versuscomputational delay. A feedback scheduling strategy for multiple MPCcontrollers is also proposed, where the scheduler allocates CPU timeto the tasks according to the current values of the cost functions.Simulated examples show how the overall control performance maybenefit from the application of the proposed schemes.
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19.
  • Henriksson, Dan, et al. (författare)
  • TinyRealTime - An EDF Kernel for the Atmel ATmega8L AVR
  • 2004
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • This report describes the design and implementation of {TinyRealTime}, an event-based real-time kernel for the Atmel AVR ATmega8L 8-bit micro-controller. The kernel is event-based and supports fully preemptive earliest-deadline-first scheduling of tasks. Semaphores are provided to support task synchronization. The focus of the report is on the memory management, timing, and internal workings of the kernel. The flash memory footprint of the kernel is approximately 1200 bytes and it occupies 11 bytes of SRAM memory for the kernel data structure plus an additional 11 bytes for each task and one byte for each semaphore. An application example is described, where the real-time kernel is used to implement concurrent control of two ball and beam laboratory processes using six application tasks.
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20.
  • Henriksson, Dan, et al. (författare)
  • TrueTime 1.1 -- Reference Manual
  • 2003
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • The manual describes the use of TrueTime, a Matlab/Simulink-based tool for simulation of distributed real-time control systems. The tool facilitates detailed co-simulation of plant dynamics, controller task execution, and network transmissions. The TrueTime Kernel and TrueTime Network blocks are described, and the real-time kernel primitives are detailed.
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23.
  • Henriksson, Dan, et al. (författare)
  • TrueTime: Real-time Control System Simulation with MATLAB/Simulink
  • 2003
  • Ingår i: Proceedings of the Nordic MATLAB Conference.
  • Konferensbidrag (refereegranskat)abstract
    • Traditional control design using MATLAB/Simulink, often disregards the temporal effects arising fromthe actual implementation of the controllers. Nowadays, controllersare often implemented as tasks in a real-time kernel and communicatewith other nodes over a network. Consequently, the constraints of thetarget system, e.g., limited CPU speed and network bandwidth, must betaken into account at design time.For this purpose we have developed TrueTime, a toolbox forsimulation of distributed real-time control systems. TrueTimemakes it possible to simulate the timely behavior of real-time kernelsexecuting controller tasks. TrueTime also makes it possibleto simulate simple models of network protocols and their influence onnetworked control loops.TrueTime consists of a kernel block and a network block, bothvariable-step S-functions written in C++. TrueTimealso provides a collection of MATLAB functions used to, e.g., do A/Dand D/A conversion, send and receive network messages, set up timers,and change task attributes. The TrueTime blocks are connectedwith ordinary continuous Simulink blocks to form a real-time controlsystem.The TrueTime kernel block simulates a computer with anevent-driven real-time kernel, A/D and D/A converters, a networkinterface, and external interrupt channels. The kernel executesuser-defined tasks and interrupt handlers, representing, e.g., I/Otasks, control algorithms, and communication tasks. Execution isdefined by user-written code functions (C++ functions orm-files) or graphically using ordinary discrete Simulink blocks. Thesimulated execution time of the code may be modeled as constant,random or even data-dependent. Furthermore, the real-time schedulingpolicy of the kernel is arbitrary and decided by the user.The TrueTime network block is event driven and distributesmessages between computer nodes according to a chosen network model.Currently five of the most common medium access control protocols aresupported (CSMA/CD (Ethernet), CSMA/CA (CAN), token-ring, FDMA, andTDMA). It is also possible to specify network parameters such astransmission rate, pre- and post-processing delays, frame overhead,and loss probability.TrueTime is currently used as an experimental platform forresearch on flexible approaches to real-time implementation andscheduling of controller tasks. One example is feedback schedulingwhere feedback is used in the real-time system to dynamicallydistribute resources according to the current situation in the system.
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24.
  • Henriksson, Dan, et al. (författare)
  • TrueTime: Simulation of Control Loops Under Shared Computer Resources
  • 2002
  • Ingår i: Proceedings of the 15th IFAC world congress.
  • Konferensbidrag (refereegranskat)abstract
    • The paper presents TrueTime, aMatlab/Simulink-based simulator for real-time controlsystems. TrueTime makes it possible to simulate the temporalbehavior of multi-tasking real-time kernels containing controllertasks and to study the effects of CPU and network scheduling on controlperformance. The simulated real-time kernel is event-driven and canhandle external interrupts as well as fine-grained details such ascontext switches. Arbitrary scheduling policies may be defined, andthe control tasks may be implemented using C functions, M functions,or Simulink block diagrams. A number of examples that illustratethe use of TrueTime are presented.
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25.
  • Lincoln, Bo, et al. (författare)
  • Jitterbug: A Tool for Analysis of Real-Time Control Performance
  • 2002
  • Ingår i: Proceedings of the 41st IEEE Conference on Decision and Control. - 0191-2216. - 0780375165 ; 2, s. 1319-1324
  • Konferensbidrag (refereegranskat)abstract
    • The paper presents Jitterbug, a Matlab-basedtoolbox for real-time control performance analysis. The controlsystem is described using a number of connected continuous-time anddiscrete-time linear systems. The control performance is measured bya continuous-time quadratic cost function. A stochastic executionmodel is used to describe when the different discrete-time systemsare updated during the control period. Building different systemmodels, the tool makes it easy to investigate how controlperformance is affected by e.g. input-output delay, sampling jitter,output jitter, lost samples, period overruns, aborted computations,and jitter compensation.
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26.
  • Persson, Patrik, et al. (författare)
  • Execution-Time Properties of a Hybrid Controller
  • 2000
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • We are interested in gaining more knowledge about the execution-time requirements of real-time control tasks, and this paper presents a system for gathering statistics of the execution times of real-time tasks. The system allows real-time code to be instrumented in order to gather, analyze, and present execution-time statistics. It has been used to instrument an existing hybrid controller to gather execution-time statistics. These statistics indicate that the worst-case execution times of the controller occur in conjunction with reference and mode changes, and that a scheduling based on that worst-case execution time leads to poor CPU utilization.
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27.
  • Sha, Lui, et al. (författare)
  • Real-Time Scheduling Theory: A Historical Perspective
  • 2004
  • Ingår i: Real-Time Systems. - 1573-1383. ; 28:2--3, s. 101-155
  • Forskningsöversikt (refereegranskat)abstract
    • In this 25th year anniversary paper for the IEEE Real Time Systems Symposium, we review the key results in real-time scheduling theory and the historical events that led to the establishment of the current real-time computing infrastructure. We conclude this paper by looking at the challenges ahead of us.
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28.
  • Årzén, Karl-Erik, et al. (författare)
  • An Introduction to Control and Scheduling Co-Design
  • 2000
  • Ingår i: Proceedings of the 39th IEEE Conference on Decision and Control, 2000.. - 0780366387 ; 5, s. 4865-4870
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The paper presents the emerging field of integrated control and CPU-time scheduling, where more general scheduling models and methods that better suit the needs of control systems are developed. This creates possibilities for dynamic and flexible integrated control and scheduling frameworks, where the control design methodology takes the availability of computing resources into account during design and allows on-line trade-offs between control performance and computing resource utilization.
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29.
  • Årzén, Karl-Erik, et al. (författare)
  • Resource-Constrained Embedded Control Systems: Possibilities and Research Issues
  • 2003
  • Ingår i: Proceedings of CERTS'03 – Co-Design of Embedded Real-Time Systems Workshop.
  • Konferensbidrag (refereegranskat)abstract
    • A survey that points out research issues and open problems in the area of integrated control and real-time scheduling. Issues that are discussed include temporal robustness, schedulability margin, optimal and direct feedback scheduling, quality-of-control, and tools.
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