embedded control and softwarefor autonomous system
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Content
ECS Introduction
Embedded control system design and
algorithm
Embedded software
Timing constraints with embedded
software
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Embedded control systemy Control physical systems output
y By setting physical systems input (cause-effect relationship)
y Tracking
y E.g.
y Cruise c
ontr
ol
y Thermostat control
y Disk drive control
y Aircraft altitude control
y Difficulty due to
y Disturbance: wind, road, tire, brake; opening/closing door
y Human interface: feel good, feel right
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Tracking
Embedded control system divided into mainly 2 categories:1. Open loop control system
2. Close loop control system
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Open loop control systemy Plant
y Physical system to be controlledy Car, plane, disk, heater,
y Actuator
y Device to control the planty Throttle, wing flap, disk motor,
y Controller
y Designed product to control the plant
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Open loop control systemy
Outputy The aspect of the physical system we are interested in
y Speed, disk location, temperature
y Reference
y The value we want to see at outputy Desired speed, desired location, desired temperature
y Disturbance
y Uncontrollable input to the plant imposed by environmenty Wind, bumping the disk drive, door opening
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Characteristics ofOpen loop systemy Feed-forward control.
y Delay in actual change of the output.
y Controller doesnt know how well thing goes.
y Simple.
y Best use for predictable systems.
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Characteristics ofClose loop system
y Feed-Back control.
y Delay in actual change of the output.
y Controller know how well thing goes.
y Typical.y Mostly use for real time systems.
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Embedded control system design
y Design of control system is a specific example of engineering design.
y The goalof control engineering design is toobtain.....
a) Configuration
b) Specification
c) Identification of key Parameter.. To meet an actual need.
y Design arranged into 3 groups
a) Establishment of goals and variable to be controlled, and definitionof specification against which to measure performance.
b) System definition and modeling.c) Control system design and integrated system simulation and analysis
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Control system design process (Algorithm)
Establish the c
ontr
olgo
als
Identify the variables to be controlled
Write the specification
Establish the system configuration
Obtain a modelof process, the
actuator, and the sensor
Describe a controller and select key
parameter to be adjusted
Optimize the parameters and analyze
the performance
3) Control
system design,
simulation, and
analysis .
2) System
definition and
modeling.
1) Establishment
of goals, variables
to be controlled,
and specification.
If the
performance
does not meetthe
specification,
then iterate the
configuration
If meet then finalize the design
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General control system analysis
y Objective
Causing output to track a reference even in the presenceof
Measurement noise
Model error
Disturbancesy Metrics
Stability
Output remains bounded
PerformanceHow well an output tracks the reference
Disturbance rejection
Robustness
Ability to tolerate modeling error of the plant
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Performance (generally speaking)
y Rise time
Time it takes form 10% to 90%
y Peak time
y Overshoot
Percentage by which Peak exceed final value
y Settling time
Time it takes to reach 1% of final value
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Future evolution of control system
robotics
FixedautomationHigh
HighFlexibility
Autonomy
Low
Low
Extended tools Control system programmable
Digital
control
system
Improvements
Vision
Human-machine
interface
supervisory
control
Improvements
Vision
Sensor
Language
Artificial
intelligence
Extensive flexibility
and autonomy
Power tool
Hand tool
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Goal of control system
y Extensive flexibility.y High levelof autonomy.
y Adaptability.
y Improved performance of a system.
y Increased productivity.
y Reliable
Some functional research areas concentrating on Artificial
intell
igence, senso
r integratio
n, co
mputer visio
n will
makesystem more universal and economical.
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Embedded software and Timing
constraint
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Embedded software
y Software with a principal role of interacting with the
physical world must, of necessity, acquire some properties
of the physical world. It takes time. It consumes power. It
does not terminate (unless it fails). It is not the idealized
procedures of Alan Turing.
y An arrogant view of embedded software is that it is just
software on small computers.
y Embedded software = RTOS + Application program.
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Embedded programming abstraction
y Timeliness
y Concurrency
y Interfaces
y
Livenessy Reactivity
y Heterogeneity
They are essential to the correctness of a program. But notsufficient to realize the right mapping from input data to
output data.
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y Timelines : The issue is not just that execution takes time.
Even with infinitely fast computers, embedded software
would still have to deal with time because the physicalprocesses, with which it interacts, evolve over time.
y Concurrency : Embedded systems rarely interact with
only a single physical process. They must simultaneouslyreact to stimulus from a network and from a variety of
sensors, and at the same time, retain timely control over
actuators. This implies that embedded software is
concurrent.
y Interface : For embedded software to benefit from a
component technology, that component technology will
have to include dynamic properties in interface definitions.
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y Liveness : In embedded systems, liveness is a critical
issue. Programs must not terminate or block waiting for
events that will never occur. In embedded computing,however, terminating programs are defective. The term
deadlock pejoratively describes premature termination
of such systems. It is to be avoided at all costs.
y Reactivity : Reactive systems are those that react
continuously to their environment at the speed of the
environment.
y Heterogeneity : Heterogeneity is an intrinsic part of
computation in embedded systems. They mix
computational styles and implementation technologies.
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Programming Languages Used in
New Embedded Designs
0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00%
Others
Assembly
Java
C#
C++
C
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Commercial operating system used
in embedded software design
0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00%
Others
Palm
Green Hills
Symbian
Wind River
Microsoft Emb.
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Embedded software: Modeling
Timing constraint
A timing constraint:
Defined with respect to some event.
An event:
Can occur at an instant of time May also have duration
Generated either by the system or its environment
Events in real time system
Stimulus Events
Response Events
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Classification ofTimingConstraints
Different timing constraints can broadly be classified into:
Performance constraints.
Behavioural constraints.
Both performance and behavioural constraints can be
classified into:
Delay Constraints
Deadline Constraints
Duration Constraints
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252503/08/10 2525
Timing Constraints
Behavioural ConstraintsPerformance Constraints
Delay Deadline Duration
RR SR RR SR
Delay Deadline Duration
RS SS RS SS
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References
y To appear in Advances in Computers (M. Zelkowitz, editor),
Vol. 56, Academic Press, London, 2002.
y E Balarin, M. Chiodo, E Giusto, H. Hsieh, A. Jurecska, L.
Lavagno, C. Passerone, A. Sangiovanni-Vincentelli, E.
Sentovich, K. Suzuki, and B.Tabbara. Hardware-SoftwareCo-Design of Embedded Systems: The Polis Approach.
Kluwer Academic Press, 1997.
y G. Berry, P. Couronne, and G. Gonthier, The synchronous
approach to reactive and real-time systems, Proc. IEEE,vol. 79, Sept. 1991.
y Real time system Prof. Rajib Mall
y Modern control system Dorf,Bishop