Presentation on Real Time Systems and Adaptive Cruise Control

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Presentation onReal Time Systems andAdaptive
Cruise Control

• Gurulingesh R.
• M. Tech. II Year, IIT Bombay
• 9th Sept 2004

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Roadmap

• Introduction to RTS
• Problem Definition / Motivation
• Adaptive Cruise Control (ACC)
• Driver Models
• Functional Model Task Model
• Extensions to Functional Model
• Conclusion Future Work
• References

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Functional Design Mapping
SourceIan Phillips, ARM VSIA 2001
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What is real about real-time?

• computer world
• e.g., PC
• average response for user
• Interactive
• occasionally longer
• reaction user annoyed
• computer controls speed of user
• computer time

• real world
• Industrial system, airplane
• environment has own speed
• reaction too slow deadline miss
• reaction damage, pot. loss of human life
• computer must follow speed of environment
• real-time

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Real-Time Systems

• A real-time system is a system that reacts to
  events in the environment by performing
  predefined actions

within specified time intervals.
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Real-Time Systems Properties of Interest

• Safety Nothing bad will happen.
• Liveness Something good will happen.
• Timeliness Things will happen on time - by their
  deadlines, periodically, ...

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In a Real-Time System
Correctness of results depends on valueand its
time of delivery

• correct value delivered too late is incorrect
• e.g., traffic light light must be green when
  crossing, not enough before
• Real-time
• (Timely) reactions to events as they occur,
  at their pace(real-time) system (internal)
  time same time scale as environment (external)
  time

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Types of RT Systems

• Dimensions along which real-time activities can
  be categorized
• how tight are the deadlines?
• --deadlines are tight when
• laxity (deadline -- computation time) is
  small.
• how strict are the deadlines?
• what is the value of executing an activity
  after its deadline?
• what are the characteristics of environment? how
  static or dynamic must the system be?

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Hard, soft, firm

• Hard -- result useless or dangerousif deadline
  exceeded
• Ex Aircraft, Chemical Plant

• Soft -- result of some - lower value if deadline
  exceeded
• Ex Multimedia, Interactive video games

-

• Firm -- If value drops to zero at deadline

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Timing Constraints

• Real-time means to be in time --- how do we know
  something is in time?how do we express that?
• Timing constraints are used to specify temporal
  correctnesse.g., finish assignment by 2pm, be
  at station before train departs.
• A system is said to be (temporally) feasible, if
  it meets all specified timing constraints.
• Timing constraints do not come out of thin
  airdesign process identifies events, derives
  models, and finally specifies timing constraints

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Overall Picture
Physical properties of environment Model-design
Timing constraints Analysis, Testing Run-time
dispatching (In field use)
Functional Temporal
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• Timing Properties
• Periodic
• activity occurs repeatedly
• e.g., to monitor environment values, temperature,
  etc.
• Aperiodic
• can occur any time
• no arrival pattern given
• Sporadic
• can occur any time, but
• minimum time between arrivals

mint
time
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Who initiates (triggers) actions?

• Example Chemical process
• controlled so that temperature stays below danger
  level
• warning is triggered before danger point
• so that cooling can still occur
• Two possibilities
• action whenever temp raises above warn-- event
  triggered
• look every int time intervals action when temp
  if measures above warn -- time triggered

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Other Issues to worry about

• Meet requirements -- some activities may run
  only
• after others have completed - precedence
  constraints
• while others are not running - mutual exclusion
• within certain times - temporal constraints
• Scheduling
• planning of activities, such that required timing
  is kept
• Allocation
• where should a task execute?

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Project Motivation
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Motivation (Cont)

• Partitioning of system into TT and ET domains
• Process Mapping
• Optimization of parameters corresponding to
  communication protocol.
• Sequence and Slots of TDMA (TTC)
• Priorities of Messages (ETC)
• Schedulability

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Adaptive Cruise Control

• Adaptive Cruise Control
• automatically adjusts vehicle speed to maintain a
  driver-selected safe distance from the vehicle
  ahead in the same lane.
• It then returns to the set speed when traffic
  clears.
• Requirements
• The speed should be kept close to the SET speed,
  if there is no vehicle ahead.
• Timegap should be maintained at x sec.
• Manual intervention, UI, etc

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Functions Identified

• Computing Current speed of our vehicle
• Leading Vehicle related Task
• Controlling Speed of our Vehicle
• Controlling the Throttle
• Controlling the Brake
• Detecting Manual Intervention
• UI to the Driver
• Periodicity of Tasks
• Hard, Firm Periodic, Aperiodic

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Human Driver Model

• Stimulus-Reaction Model

Structure of Human Driver in Car-Following
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Car Following Models

• Linear Follow-the-Leader Model
• Stimulus Velocity Difference b/w Leader and
  Follower
• Reaction Acceleration command to vehicle
• Look-Ahead-Model
• Driver observes the behavior of three vehicles
  ahead of him.
• Stimulus Majority direction of Acceleration
• Reaction Acceleration command using switching
  logic
• Others

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Simple Car Following Model
vl Velocity of Leader vf Velocity of
Follower rl Retardation of Leader rf
Retardation of Follower tr Short Reaction
Time
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Acceleration profile of vehicle
Dmin Di Di-1 Di D1i D2i D3i
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ACC System Design
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Process Model
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Pictorial View
Sensors
Actuators
Friction Estimator
Schematic Picture of Control Algorithm and its
Environment
Throttle System
Speed Sensor
Control Algorithm
Radar System
ABS
Roadside Signals
as
SPEED Module
The structure of Control Algorithm
Min-value
Control Signal to the Actuators
DISTANCE Module
ad
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Block Diagram
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Flow Chart
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Flow Chart (cont)
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State Diagram
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Precedence Graph showing communication relation
Curr_Thr Pos
Curr_Br Pos
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Task Graph
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Extensions to Functional Model under consideration

• Adaptive to
• Driver Reaction Time
• Roadside Signals
• Friction b/w road and tyre (ABS)
• Relative positioning in the lane

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Future Work

• Partitioning tasks as TT and/or ET and as Soft,
  Hard or Firm.
• Writing Algorithm
• Allocation of Tasks
• Schedulability
• One or two similar application if time permits

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Some of the References

• K. Ramamritham, Slides from Embedded
  Systems(IT606) course.
• Paul pop et. al. Design Optimization of
  Multi-Cluster Embedded Systems for Real-Time
  Applications, Date04, Paris, France, February
  16-20, 2004, pp. 1028-1033 .
• Krithi Ramamritham, Allocation and Scheduling of
  Precedence-Related Periodic Tasks, IEEE
  Transaction in Parallel and Distributed Systems,
  1995, pp. 412-420.
• Jakob Axelsson, A case Study in Heterogeneous
  Implementation of Automotive Real-Time Systems,
  6th International Workshop on Hardware/Software
  CoDesign, Seattle, March 15-18, 1998.
• Cecilia Ekelin, Jan jonsson, Real Time System
  Constraints Where do they Come From and where do
  they Go?, In Proceedings of the Intl Workshop
  on Real Time Constarints, Oct. 16, 1999, USA, pp.
  53-57.
• Kristina Ahlström, Jan Torin, Design Method for
  Conceptual Design of By-Wire Control Two Case
  Studies, 7th Intl conference on Engineering of
  Complex Computer Systems, June 11-13, 2001.