| 1. |
- Bate, Iain, et al.
(författare)
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Establishing Timing Requirements and Control Attributes for Control Loops in Real-Time Systems
- 2003
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Ingår i: Proceedings 15th Euromicro Conference on Real-Time Systems, 2003.. - 0769519369 ; , s. 121-128
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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)
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Feedback-Feedforward Scheduling of Control Tasks
- 2002
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Ingår i: Real-Time Systems. - 1573-1383. ; 23:1-2, s. 25-53
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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
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Ingår i: Proceedings of the 39th IEEE Conference on Decision and Control, 2000.. - 0780366387 ; 5, s. 4871-4876
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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
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Ingår i: Control Systems Magazine. - 0272-1708. ; 23:3, s. 16-30
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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
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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
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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
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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)
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The Control Server: A Computational Model for Real-Time Control Tasks
- 2003
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Ingår i: Proceedings 15th Euromicro Conference on Real-Time Systems, 2003.. - 0769519369 ; , s. 113-120
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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.
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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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