RealTime Scheduling Chapter 5.5

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Real-Time SchedulingChapter 5.5

• Aravind Venkataraman

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Topics of Discussion

• Real-time Computing
• Synchronous Programming Languages
• Real-time Operating Systems
• Real-time System Types
• Real-time System Key factors, terminology
• Real-time System Methodologies
• Real-time Scheduling Algorithms
• Real-time Scheduling Implementation Issues
• Real-time Computing Research Key People

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Real time Computing 1

• 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.

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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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Real-time System Types

• Hard Real-time System - Guaranteed,
  deterministic behaviour.
• - Critical Jobs.
• - Eg. Nuclear Power Plant
  controller.
• Soft Real-time System - High Throughput.
• - Concurrent
  access, Large demand.
• - Eg. Airline
  Reservation System.

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Hard deadline
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Soft deadline
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Real-Time System Key Factors Burns, 91

• Minimal Interrupt Latency
• Minimal Thread switching Latency

Other Terminology

• Task Deadline
• Maximum Response Time
• Worst case Execution Time
• Timing Analysis
• Priority Inversion
• Priority Inheritance
• Priority Ceiling Protocol.

Important Real-time System Property Stankovic,
84

• System Deadline gt Process Deadline
• Periodic, Aperiodic Process.

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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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Key People in Real-time Computing

• Edward Lee - UC Berkeley, Ptolemy Project
• - http//ptolemy.eecs.berkeley.ed
  u/eal/
• Alan Burns, Andy Wellings - Univ of York, RT
  Systems Research group
• - http//www.cs.york.ac.uk/rts/
• David Dill - Stanford University - Formal
  verification in RT Systems design
• - http//verify.stanford.edu/dill/
• Rajeev Alur - Univ of Pennsylvania - Hybrid
  systems, formal modeling, verification of
  reactive systems Automata Theory
• - http//www.cis.upenn.edu/alur/
• Nicolas Halbwachs - Grenoble University,
  Critical embedded systems, data flow synchronous
  programming languages
• - http//www-verimag.imag.fr/halbwach/

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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
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References

• http//en.wikipedia.org/wiki/Real-time_operating_s
  ystem
• 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).
• 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).
• A. Burns, Scheduling Hard Real-Time Systems A
  Review, Software Engineering Journal 6(3), pp.
  116-128 (1991).
• K. Ramamritham and J.A. Stankovic, Dynamic Task
  Scheduling in Hard Real-Time Distributed
  Systems, IEEE Software 1(3), pp. 65-75 (July
  1984).
• http//www.aadl.info/
• http//www.rtsj.org/
• http//ptolemy.eecs.berkeley.edu/