Real-Time Design

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Real-Time Design

• Richard Gharaat

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Time-Relevant Systems Vs. Time-Irrelevant Systems

• Time-irrelevant systems dont care about time at
  all.
• Example
• A system to print out reunion invitation cards
  for all CS graduates.
• Time-relevant systems deal with data with respect
  to time.
• Example
• A reporting system that reads in data of a period
  of time and makes a report or analyze it (Tax
  return).
• A billing system that checks if the bill has been
  paid before due date.

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Real-Time Systems

• They deal with data regarding the CURRENT time.
  There is some forbearance for malfunctioning,
  they can be restarted or reset.
• Example
• Sampling systems
• Feed-back systems
• Control systems
• Media players

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Time-Critical Systems

• Current time is the main concern of the system.
  The task must be done within a very short
  deadline. There is NO forbearance to malfunction
  or restart.
• Example
• Car brake system (ABS).
• Medical radiotherapy systems. (Therac 25)
• Missile control system / navigator (Ariane 5)

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Real-Time System Categorization

• Soft systems
• Machinery condition monitoring
• Man - Machine interfacing
• Games
• Hard systems
• Missile point defense system
• Airbag control system
• Embedded systems

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Real-Time Design

• Hard, fast embedded systems tend - in computing
  terms - to be small.
• Computation times are short and deadlines are
  critical.
• Software complexity is usually low.
• They are mostly event driven.

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Important Questions

• How fast?
• How large?

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Timing And Sequence Issues

• The whole point of using STDs is to show how
  system changes with time. Yet time itself hasnt
  been explicitly mentioned. The reason is our STD
  model of reality shows that
• Systems have a set of discrete, unique states
• Each state exists for a time determined by system
  events or conditions
• Transitions between states take zero time.

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Real-Time Data Flow Diagram
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Where to Get More Information

• J.E. Cooling 1997, Real-Time Software Systems
• An Introduction to Structured and Object-Oriented
  Design
• Booch Jacobson Rumbrugh 1998, Real-time UML
• Developing Efficient Objects for Embedded Systems
• Raymmond J.A. Buhr Donald L. Bailey 1999, An
  Introduction to Real-Time Systems
• From Design to Networking With C/C
• Luciano Lavagno Grant Martin Bran Selie 2003,
  UML for Real
• Design of Embedded Real-Time Systems