presentation on real time systems and adaptive cruise control
TRANSCRIPT
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Presentation on
Real Time Systems andAdaptive Cruise Control
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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
HW1 HW2 HW3 HW4Hardware Interface
RTOS/Drivers
Thr
eadArchitectural
Design
F1F2
F3
F4
F5Functional
Design
(F3) (F4)
(F5)
(F2)
Source:Source:Ian Phillips, ARMIan Phillips, ARM
VSIA 2001
Source:Source:Ian Phillips, ARMIan 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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A real-time system is a system that reacts to events in the environment by performing predefined actions
I/O - data
I/O - data
Real-Time Systems
Real-timecomputing system
event
action
within specified time intervals.
time
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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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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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deadline (dl)
+
Hard, soft, firm
• Hard -- result useless or dangerousif deadline exceeded
Ex: Aircraft, Chemical Plant value
time
-
hardsoft
• 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 ConstraintsReal-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 air:design 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
Structure of Human Driver in Car-Following
• Stimulus-Reaction Model
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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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Src: Prof. Shashikant's Control System Lec-1 in DEP Mode
ACC System Design
(desired vehicle speed)(desired vehicle speed)
Control I/PControl I/PPhysical Physical ProcessProcess
SensorsSensors
ActuatorsActuators
AdaptiveAdaptive
Cruise Cont.Cruise Cont.
Reference InputReference Input
Actual outputActual output
Sensor NoiseSensor Noise
Actuator NoiseActuator Noise
Sensed O/PSensed O/P
DesiredDesired
Control I/PControl I/P
DisturbancesDisturbances(accelerator pedal (throttle) position, brake pedal position)(accelerator pedal (throttle) position, brake pedal position)
(wheel speed sensor)(wheel speed sensor)
(air drag, grade,(air drag, grade,
friction etc)friction etc)
(vehicle speed)(vehicle speed)
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Src: Prof. Shashikant's Control System Lec-1 in DEP Mode
Process Model
Physical Physical ProcessProcess
Actual OutputActual Output
Control I/PControl I/P
DisturbancesDisturbances
EE 1/M1/MGG 1/R1/Rww
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Pictorial View
Friction Estimator
Speed Sensor
Radar System
Roadside Signals
Control Algorithm
Throttle System
ABS
ActuatorsSensors
Schematic Picture of Control Algorithm and its Environment
SPEED Module
DISTANCE Module
Min-value
Control Signal to the Actuators
The structure of Control Algorithm
as
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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g
a
b
Wheel S
IR S
f
Speed Set
Throttle S
Brake S
c
d
e
Throttle A
Brake A
Curr_Thr Pos
Curr_Br Pos
Precedence Graph showing communication relation
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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