Issues (cont…)
3. All Tasks and Data throughout the system operation??
•AdaptT when lead car is near
•AdjLaneT, TimeLeftT when car is far
Poor CPU utilization Scheduling Overhead Not modular
Approach
• Mode-Change System
– Exclusive modes of operation – Mode change leads to:
• Addition of a task • Change in frequency of execution • Deletion of a task
• Data Repository
(Neera Sharma)
– updates in response to changes in the data items (on-demand update).
Approach (cont…)
• Mode-Change System
– Dynamically varying data – All Tasks and Data throughout the system operation
• Data Repository
– Dynamically varying data – Derived Data Items
Issues
• With mode-changes:
– How many modes – What triggers mode change – When to switch mode – Chattering – Mode-change delay – Schedulability
• With Data Repository
– How many levels – When to update
Solution to mode-change
• How many?
– Two: Safety-Critical(SC), Non-Safety Critical(NC)
• When to switch?
– Finish task execution.
• Mode-change delay
– Bounded by longest periodicity task.
• Schedulability
– Static checking.
Solution to mode-change…
• What triggers mode change?
LeadDist RoD OR OR
LeadDist FAR RoD DECR-FAST Mode SC
Further Work
• More experiments to evaluate the design.
• Implementing two-level repository on RealTime Data Base.
• Is printer port good enough or need for RTCommunication (TTP/TTCAN/CAN). • Merging with Lane Changing.
• Inter-Vehicle communication.
• Formal modeling using UPPAAL/KRONOS.
Goals Revisited
• Study the ACC application and to identify
– Components – Algorithms – Real-Time Issues
• Real-Time approach to Design • Setup a basic platform
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”. Technical Report: UM-CS-1989-060, University of Massachusetts Amherst, MA, USA.