Niranjan Rao Julapelly

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Real-Time SchedulingChapter 5.5

• Niranjan Rao Julapelly

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Topics of Discussion

• Real-time Computing
• Synchronous Programming Languages
• Real-time Operating Systems
• Real-time System Types
• Real-time System Methodologies
• Real-time Scheduling Algorithms
• Real-time Scheduling Implementation Issues

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Real time Computing

• Software hardware for systems which have
  real-time constraints and are interrupted often.
• Comprises of
• Synchronous Programming Language.
• Real-time Operating System.
• Real-time Design Methodologies.

Synchronous Programming Language

• Provides abstract modules for scheduling
  algorithms, parallelism, pre-emption.
• Finite state (execution time predictable),
  deterministic, synchronous dataflow.
• Declarative and Imperative Languages.
• Examples Lustre, Quartz, SOL, Esterel.

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Real-Time Operating System (RTOS)

• Examples Embedded Systems (Appliance
  Controller, Spacecraft, Robots, Industrial
  Control.

Early Real-time Systems

• Control Program American Airlines, IBM
  Later called Sabre Airline Reservation System.

Recent Important Real-time Systems

• DSOS (Deep Six OS) Geophysical Services
  Division, Texas Instruments.
• Ptolemy Project, University of California,
  Berkeley 8.
• MARS (MAintainable Real-time System).
• ARTS Kernel.
• Spring Kernel.
• CHAOS Kernel.
• Alpha Kernel .
• Dragon Kernel.

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Hard Real Time vs. Soft Real Time McObject,
2006

• Critical real-time systems such as nuclear
  power plants or fly-by-wire airplanes are
  Hard Real Time
• Non-critical real time systems where missed
  transactions only degrade system quality are Soft
  Real Time
• Firm real-time systems are similar to soft
  real-time, except late tasks are discarded.
• Scheduling algorithm depends on real time
  system characteristics

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Hard deadline
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Soft deadline
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Real-time System Design Methodologies

• MASCOT (Modular Approach to Software
  Construction Operation and Test)
• - Architecture Oriented (RT Control
  interface definition between concurrent
  processes)
• - British ground-air missile system.
• HOOD (Hierarchic Object-Oriented Design)
• - Hierarchical decomposition.
• - European Space Agency Aerospace project.
• AADL (Architecture Analysis and Design Language)
  6 - Automotive, aerospace industry.
• RTSJ (Real-Time Specification for Java) 7

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Real-time Scheduling Algorithms Stankovic,88

• Classification
• Static vs Dynamic
• Preemptive vs Non-preemptive
• Global vs Local

• Examples
• Static
• - Fixed-priority Rate-monotonic algorithm
• - Fixed-priority Deadline-monotonic algorithm
• - Graph based Approach
• Dynamic
• - Earliest Deadline First
• - Least Laxity

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Real-time Implementation issues in Distributed
Systems Kasavant, 88

• Communication Delay - worst case execution time,
  non-deterministic
• RPC - Remote blocking

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RT Research Groups

• RT computing lab http//www.eecs.umich.edu/RTCL/
  
• RT computation and communication group
  http//www.cs.bu.edu/groups/realtime/
• RT and embedded systems laboratory
  http//www.cs.virginia.edu/control/
• Supercomputing and Parallel computing research
  group http//www.cs.cmu.edu/scandal/research-gro
  ups.html
• Systems Research group http//www.cc.gatech.edu/
  systems/
• Distributed systems research group
  http//www-dsg.stanford.edu/
• Institute for systems engineering, RT Systems
  group
  
  http//www.rts.uni-hannover.de/index.php/Main_Pa
  ge/index.htm
• Institute for computer engineering, RT Systems
  group http//www.vmars.tuwien.ac.at/

RT Technical Commitees

• IEEE Technical Committee on Real-Time Systems
  http//cs-www.bu.edu/pub/ieee-rts/
• Euromicro Technical Committee on Real-time
  Systems http//www.ecrts.org

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RT Scientific conferences
Event Website
IEEE Real-time Technology and Applications Symposium, St. Louis, Missouri, USA - April 22-24, 2008 http//www.rtas.org/
ECRTS Euromicro Conference on Real-time Systems http//www.ecrts.org/
IEEE Real-time Systems Symposium, Tuscon, Arizona, USA Dec 3-6, 2007 http//www.rtss.org/
International Symposium on Object oriented Real-time Distributed systems http//ise.gmu.edu/isorco7
IEEE International Conference on Embedded and Real-time Computing systems and Applications http//ssl.snu.ac.kr/rtcsa2007/
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References

1. http//en.wikipedia.org/wiki/Real-time_operating_s
   ystem
2. S. Cheng, J.A. Stankovic and K. Ramamritham,
   Scheduling Algorithms for Hard Real-Time
   Systems A Brief Survey, pp. 150-173 in Hard
   Real-Time Systems Tutorial, IEEE (1988).
3. T. L. Casavant and J. G. Kuhl, A Taxonomy of
   Scheduling in General Purpose Distributed
   Computing Systems, IEEE Transactions on
   Software Engineering 14(2), pp. 141-154 (February
   1988).
4. A. Burns, Scheduling Hard Real-Time Systems A
   Review, Software Engineering Journal 6(3), pp.
   116-128 (1991).
5. K. Ramamritham and J.A. Stankovic, Dynamic Task
   Scheduling in Hard Real-Time Distributed
   Systems, IEEE Software 1(3), pp. 65-75 (July
   1984).
6. McObject LLC, Real-time Databases for Embedded
   Systems, Precision Data Management, 2006