Towards the Integration of Control and Real-Time Scheduling Design Cervin, Anton

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Towards the Integration of Control and Real-Time Scheduling Design
Cervin, Anton
2000
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Cervin, A. (2000). Towards the Integration of Control and Real-Time Scheduling Design. [Licentiate Thesis,
Department of Automatic Control]. Department of Automatic Control, Lund Institute of Technology (LTH).
Total number of authors:
1
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LUND UNIVERSITY
PO Box 117
221 00 Lund
[phone]
Towards the Integration of
Control and Real-Time
Scheduling Design
Anton Cervin
Department of Automatic Control
Lund Institute of Technology
Lund, Sweden
Department of Automatic Control DLocIuCmEenNtTnaIAmTeE THESIS
Lund Institute of Technology
Box 118 DMateaoyf2is0su0e0
SE-221 00 Lund Sweden
DIoScuRmNentLNUuTmFbDer2/TFRT--3226--SE
( )
AuAtnhotrons Cervin SuKpaerrvli-sEorrik Årzén
Bo Bernhardsson
SpAoRnsTorEinSg/oSrgSaFnisation
TiTtloewaandrdssubtthiteleIntegration of Control and Real-Time Scheduling Design
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
lossduetojitterandcontroldelays.Anothergoalistorelaxthenominalrequirementsonharddeadlines
andfixedworst-caseexecutiontimes.Athirdgoalistoprovidea co-simulationenvironmentforreal-time
control systems.
Sub-task scheduling of the two main parts of a control algorithm is investigated. A heuristic, iterative
deadline-assignment algorithm is given that attempts to minimize the computational delay for a set of
control tasks.
Asimulatorfor co-designofreal-timecontrolsystemsispresented.Itfacilitatessimultaneoussimulation
of real-time task execution and continuous plant dynamics. The simulator makes it possible to evalu-
ate the true, timely behavior of control algorithms, and to evaluate scheduling policies from a control
performance perspective.
A feedback scheduler for control tasks with varying execution times is developed. Using a combination
of feedback andfeedforward, thefeedback scheduler attemptsto keep theCPU utilizationatthe desired
level by manipulatingthe sampling periods of the controllers. A case-study with a set of hybrid control
tasksfor a set of double-tank processes is presented.
KReyewaol-rTdsime Control, Scheduling, Co-Design, Deadlines, Performance, Simulation, Feedback
/ ( )
Classi(cid:2)cationsystemand orindexterms ifany
Supplementarybibliographical information
IS0S2N8a0n–d5k3e1y6title ISBN
LaEnnggualigseh N1u5m2berofpages Recipient’snotes
Securityclassi(cid:2)cation
Thereportmaybeorderedfrom-theDepartmentofAutomaticControlorborrowedthrough:
Univ+ersity Library2,Box3-,SE22100Lund,Sweden
Fax [phone] [email protected]
Towards the Integration of
Control and Real-Time
Scheduling Design
Anton Cervin
Department of Automatic Control
Lund Institute of Technology
Lund, May 2000
Department of Automatic Control
Lund Institute of Technology
Box 118
SE-221 00 LUND
Sweden
E-mail: [email protected]
WWW: http://www.control.lth.se/˜anton
ISSN 0280–5316
/
ISRN LUTFD2 TFRT--3226--SE
&c 2000 by Anton Cervin. All rights reserved.
Printed in Sweden by Universitetstryckeriet,
Lund University, Lund 2000
Contents
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Background and Motivation . . . . . . . . . . . . . . . . 9
2. Outline, Contributions, and Related Publications . . . . 10
3. Deadlines in Real-Time Control Systems . . . . . . . . . 13
4. Inverted Pendulum Experiments . . . . . . . . . . . . . . 23
5. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 32
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
1. Towards the Integration of Control and Real-Time Schedul-
ing Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2. Real-Time Scheduling Theory . . . . . . . . . . . . . . . 42
3. Sampled-Data Control Theory . . . . . . . . . . . . . . . 47
4. Timing in Simple Control Loops . . . . . . . . . . . . . . 51
5. Flexible and Adaptive Scheduling . . . . . . . . . . . . . 63
6. Research Issues . . . . . . . . . . . . . . . . . . . . . . . 73
7. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
2. Improved Scheduling of Control Tasks . . . . . . . . . . 93
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 94
2. Periodic Sampling . . . . . . . . . . . . . . . . . . . . . . 96
3. Scheduling . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4. Delay Compensation . . . . . . . . . . . . . . . . . . . . . 101
5. An Example . . . . . . . . . . . . . . . . . . . . . . . . . . 102
5
Contents
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 109
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 109
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
3. A Matlab Toolbox for Real-Time and Control Systems
Co-Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 114
2. The Basic Idea . . . . . . . . . . . . . . . . . . . . . . . . 116
3. The Simulation Model . . . . . . . . . . . . . . . . . . . . 117
4. Using the Simulator . . . . . . . . . . . . . . . . . . . . . 121
5. A Co-Design Example . . . . . . . . . . . . . . . . . . . . 126
6. Simulation Features . . . . . . . . . . . . . . . . . . . . . 129
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 132
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 132
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
4. Feedback Scheduling of Control Tasks . . . . . . . . . . 135
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 136
2. A Hybrid Controller . . . . . . . . . . . . . . . . . . . . . 139
3. Feedback Scheduling Example . . . . . . . . . . . . . . . 142
4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 149
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
6
Acknowledgments
Acknowledgments
Starting my graduate studies two years ago, I had the great advantage
of joining a fresh, exciting, and well-defined research project, where
several interesting problems were just waiting to be mined.
First, of course, I would like to thank my supervisor Karl-Erik
Årzén. He, together with Klas Nilsson and Ola Dahl, wrote the original
proposal for the project “Integrated Control and Scheduling”. I admire
his efficiency and his sound attitude towards research and work in
general.
Johan Eker’s input to this project cannot be overstated. Believe it
or not, but I do enjoy working with him, and I look forward to further
collaborative efforts.
The ideas on feedback scheduling were originally the brainchild of
Lui Sha. I got my basic training in real-time systems from him when
I spent two months at the Software Engineering Institute, Carnegie
Mellon University, in the summer of 1998. I would also like to extend
my gratitude to Danbing Seto.
Everybody at the department has been most helpful and friendly!
My co-supervisor Bo Bernhardsson has provided several valuable com-
ments. Karl Johan Åström lured me into the field of Automatic Control
and encouraged me to become a graduate student.
This project is a collaboration with the Department of Computer
Science, Lund Institute of Technology. It is a pleasure to work together
with Patrik Persson and Klas Nilsson.
D
This work has been sponsored by ARTES A network for Real-Time
E
research and graduate Education in Sweden , which is a research pro-
D E
gramme under SSF Swedish Foundation for Strategic Research . A
travel grant from the Royal Physiographic Society is also gratefully
acknowledged.
Finally, I would like to thank my wife Anna for her encouragement,
support, and love.
Anton
7
Acknowledgments
8
Introduction
1. Background and Motivation
Real-time control plays an important part in modern technology. For
example, engine management systems for cars increasingly rely on
real-time computations and feedback control to improve performance,
reduce fuel consumption, and minimize the amount of pollutant emis-
sions. At the same time, as the capacity of microcontrollers is increas-
ing and the cost is decreasing, all sorts of functionality is migrating
from hardware to software. A control task may thus be executing in
parallel with several other tasks, including other control tasks. This
puts focus on scheduling, i.e. the choice of which task to execute at a
given time. Since the beginning of the 1970s, the academic interest in
real-time scheduling has been very large. Very little of this work has,
however, focused on control tasks in particular. On the other hand,
digital control theory, with its origin in the 1950s, does not directly
deal with the resource constraints of the computing system. Instead,
it is commonly assumed that the controller executes as a simple loop
in a dedicated computer.
This work aims at getting the best possible control performance
from limited computing resources. To accomplish this goal, integration
of the real-time scheduling design and the control design is neces-
sary. Today, real-time control design is typically a two-step procedure;
control design followed by real-time design. This leads to sub-optimal
9