Real Time Systems

1
Real Time Systems

• Introduction
• to
• Real-Time Systems

2
Outline

• Definitions
• Applications of real-time computer systems
• Lifecycles
• Methodologies
• Tools

3
Definitions

• Real-Time System
• A real-time system is a software system that
  maintains an ongoing and timely interaction with
  its environment
• Bran Selic

4
Definitions (contd)

• Real-Time System
• We can think of real-time systems as those
  that react to external inputs and in a timely
  manner affect the environment in which they
  operate

5
Definitions (contd)

• Real-Time System
• any system in which the time at which output
  is produced is significant. This is usually
  because the input corresponds to some movement in
  the physical world, and the output has to relate
  to that same movement
• The Oxford Dictionary of Computing

6
Definitions (contd)

• Key characteristics of all the definitions
• timeliness
• timeliness correctness
• interaction with its environment
• hardware interfaces

7
Definitions (contd)

• Arent all computer systems real-time
• while almost all software does interface to
  hardware, Windows, Icons, Menus and Pointers
  (WIMP) programming is NOT considered real-time

?
8
Definitions (contd)

• Hard versus soft real-time
• hard real-time systems require that strict time
  deadlines are met the strictest are when an
  event must occur at time x, not just by time x.
• in soft real-time systems timeliness of events is
  important but not necessarily critical.
• Often expressed as
• x out of y events be on time, or
• by x time some slack

9
Definitions (contd)

• Real-time versus embedded software
• most real-time software is embedded within some
  larger system, and is usually the de facto
  central nervous system.
• therefore quite often real-time and embedded are
  used interchangeably when referring to the
  software of real-time systems.

10
Applications of real-time systems

• process control
• nuclear power plant
• production control
• automobile assembly line
• communication, command control
• air traffic control system
• embedded systems
• TV Satellite receiver

11
Life Cycles of real-time systems

• Small embedded commercial applications
• typically one-shot
• field and (hope to) forget
• high multiples
• cost driven efficiency requirements

12
Life Cycles (continued)

• Larger real-time systems
• (including most Military applications)
• generally subject to constant change
• very long life-cycles
• expensive to maintain
• robust designs are critical

the subject of this course
13
Methodologies

• A (very) simplified history
• flowcharts
• subroutines (functions procedures)
• structured programming
• data flow analysis
• structured analysis and design (data)
• real-time SAAD
• OOAD / UML 1.x
• ROOM / RT-UML
• UML 2.0

14
Methodologies (contd)

• Real-time Object-Oriented Modeling (ROOM)
• a method for modeling and executing large scale
  real-time systems
• originated at Nortel for the specification and
  design of telephone switching systems
• ROOM UML gt UML 1.3 (real-time semantics)
• basis of your one text
• UML 2.0
• Available in CASE tools now!
• Incorporates much of ROOM

15
Tools

• ObjecTime? Developer
• based upon ROOM (not UML)
• models based upon active objects - actors
• supports execution of the model at all stages
• simulation executable (Rapid Prototyping language
  (RPL))
• target executable (C, C)

• with the purchase of ObjecTime by Rational
• Developer becomes RoseRT
• with the purchase of Rational by IBM
• RoseRT becomes Rational Technical Developer

16
Tools (continued)

• RoseRT
• based upon UML
• uses stereotyping for domain specific semantics
• supports the Unified (software development)
  Process
• encourages rapidity of executable releases
• the micro-cycle
• translative versus elaborative

The current RMC installation is still RoseRT
and not Technical Developer
17
Tools (contd)

• Rhapsody by I-Logix
• Tau Developer by Telelogic
• Real-Time Studio by Artisan
• all based upon standard UML
• all encourage rapidity of executable releases
• also mostly translative (versus elaborative)
• There are alternatives!!
• RMC is not in the business of selling any
  specific tools

18
Summary

• Real-time and distributed systems design has
  proven to be one of the most difficult and
  intricate problems ever faced. This is primarily
  because of the complexity of the real world in
  which these systems operate. Their environment
  can be bewilderingly diverse, dynamic, and
  unpredictable - components fail at random,
  communications are corrupted, interruptions occur
  when they are most inappropriate, and so on.
• ROOM text