Post on 18-Apr-2015
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Efficient Real-Time Support for Automotive Applications: A Case Study
Gurulingesh R.
Gurulingesh R., Neera Sharma , Krithi Ramamritham, Sachitanand Malewar
Indian Institute of Technology BombayINDIA
Motivation(1/2)• Rapid increase of computer-controlled functions in
automotive applications– e.g.: New Mercedes S-class cars employ atleast 70 networked
ECUs
• Independent black-box implementation is practically infeasible:– Cost, Integration Complexity
Motivation(2/2)
• Safety-critical applications:– Brake-by-Wire, Collision Avoidance system,
Adaptive Cruise Control, etc…– deal with critical data and deadline bound
computations– have stringent requirements on:
• Freshness of data• Completion time of tasks
Introduction to ACC (1/2)
• Adaptive Cruise Control tries to maintain:
• Safe Distance when there is a leading vehicle
• Set Speed when there is no leading vehicle in its path
Introduction to ACC (2/2)
• Extension of Cruise Control.
• Operates either in
• Distance Control state
• Speed Control state
Des_Dist = Host_Vel * Timegap + ∆ where
Host_Vel is Host Vehicle velocity
TimeGap is set by the driver
∆ for additional safety
Focus of Our Work
• Efficient utilization of computing resources while satisfying safety-critical properties
Issues (1/3)
1. Effective tracking of dynamically varying data.
… …
General Practice: Prepare for the Worst
Over-Sampling
…
Di
st
Time
Issues (2/3)
Unnecessary Updates
2. Timely updates of derived data
WS1 WS2 WS3 WS4
HostVel
W4 W1 W2 W3 Radar
RDist RSpeed
LeadDist LeadVel
General Practice: Periodic updates
Issues (3/3)
3. Some tasks will execute only in some modes
Poor CPU utilization
Not modular
Scheduling Overhead
• Adapt parameters when lead car is far
• Sense adjacent lane, time to collision when car is near
General Practice: Single mode design for simplicity
Our Approach(1/3)
1. Dual Mode System:
• Two mutually exclusive phases of operation– Safety Critical Mode– Non Safety Critical Mode
• Current mode depends on:– Distance of Separation– Rate of change of Distance
LeadDist RoD Mode
FAR DECR-FAST SC
FAR INCR-FAST NC
FAR DECR-SLOW NC
FAR INCR-SLOW NC
CLOSE ---- SC
FOLLOW ---- RETAIN
Our Approach(2/3)
2. Real-Time Data Repository:
• Two level data store– Environment Data Repository– Derived Data Repository
• Task Scheduling– Constant Bandwidth Server (CBS)
Our Approach(3/3)
2. Real-Time Data Repository:
Hierarchical ACC Controller
Upper-level controller
Lower-level controller
(EDR)
Current status
Stable store
Log currentstatus
Raw data-items
Base data-items
host_vel
ang_vel
Sensor parameters
Controller constants
To actuators
Update DDR
store desired velocity
Read sensor values
` Read DDR
On demand
update
lead_vel
separation
radar_data
(DDR)
Robotic Vehicle: Experimental Setup
Capabilities:• Obstacle detection Range
– 2m
• Maximum speed– 0.50 cm/s
• White-line following
Results & Observations
• Basic Experiments: 1. Cruise Control Set Speed = 25 cm/s
Results & Observations (cont…)
• Basic Experiments: 2. ACC: Varying Velocity
- Velocity Response
Results & Observations (cont…)
• Basic Experiments: 2. ACC: Varying Velocity
- TimeGap
Results & Observations (cont…)• Basic Experiments:
– 1. Cruise Control• Set Speed = 25 cm/s
– 2. Adaptive Cruise Control• Varying Velocity
1. ACC tries to maintain:
Set speed when there is no leading vehicle
Safe Distance when there is leading vehicle
2. Variation in graphs due to Shaft Encoder error
Results & Observations (cont…)• Real-Time Data Repository Experiments:
– Task under observation: DistT (which updates DoS)– Threshold Value: 5cm– Leading vehicle with uniform speed
Results & Observations (cont…)• Real-Time Data Repository Experiments:
– Task under observation: DistT (which derives DoS)– Threshold Value: 5cm– Leading vehicle with varying speed
Results & Observations (cont…)
• Real-Time Data Repository Experiments:
– Task under observation: DistT (which derives DoS)– Threshold Value: 5cm– Time Window: 0-12 sec
DistT Task Invocation
Leading Distance With 2-level Without 2-level
Const 3 40
Incr-Decr 16 40
Results & Observations (cont…)• Real-Time Data Repository Experiments:
– Task under observation: DistT
DistT Task Invocation
Lead Dist With 2-level No 2-level
Const 3 40
Incr-Decr 16 40
– Threshold Value: 5cm
1. Less number of Updates
2. Compared to conventional approach:
Efficient usage of computing resource
Functionality/Safety not affected
Results & Observations (cont…)• Dual Mode Experiment:
– Mode change criteria: Lead Dist ≤ 65 cm/s– Periodicity of tasks: P(SC mode) = ½ * P(NC mode)
Results & Observations (cont…)
• Dual Mode Experiment:
– Mode change criteria: Lead Dist ≤ 65 cm/s– Periodicity of tasks: P(SC mode) = ½ * P(NC mode)
Results & Observations (cont…)• Dual Mode Experiment:
– Mode change criteria: • leading distance: 65 cm/s
– Periodicity of Tasks: • P(SC Mode) = ½ * P(NC Mode)
1. Compared to conventional approach:
Efficient usage of computing resource
Functionality/Safety not affected
2. Conservative Approach while deciding SafeDist
Contributions
• Presented issues involved in developing real-time support for ACC
• Efficiently utilized processor capacity by designing ACC using following concepts:
• Mode change• Real-time data repository
• Provided scheduling strategies to meet timing requirements
Ongoing Work
• More analysis of the system design (mode-change criteria, threshold values, etc.)
• Application needs are being mapped to distributed platform
• Study of controller’s stability and performance
• Usage of communication protocols such as CAN or TTP
References• Petros Ioannou; Cheng-Chih Chien. “Autonomous Intelligent
Cruise Control”. IEEE Trans. On Vehicular Technology, 42(4):657-672, 1993.
• Thomas Gustafsson; Jörgen Hansson. “Dynamic on-demand updating of data in real-time database systems”.
In Proceedings of ACM SAC 2004.
• Gerhard Fohler; “Flexibility in Statically Scheduling Real-Time Systems”. PhD Thesis, Technischen Universitat Wien Austria, Apr. 1994.
• L. Sha; R. Rajkumar; J. Lehoczky; K. Ramamritham. “Mode Change Protocols for Priority-Driven Preemptive Scheduling”. In Journal of Real Time Systems, 1(3):243-265, Dec 1989.
THANK YOU
Embedded Real-Time Systems Group
Indian Institute of Technology Bombay
INDIA
http://www.it.iitb.ac.in/car/