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Real-Time Design

Real-Time Design. Richard Gharaat. Time-Relevant Systems Vs. Time-Irrelevant Systems. Time-irrelevant systems don’t 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:

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Real-Time Design

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  1. Real-Time Design Richard Gharaat Richard Gharaat, SPSU, Fall 2008

  2. Time-Relevant Systems Vs. Time-Irrelevant Systems • Time-irrelevant systems don’t 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. Richard Gharaat, SPSU, Fall 2008

  3. 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 Richard Gharaat, SPSU, Fall 2008

  4. 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) Richard Gharaat, SPSU, Fall 2008

  5. Real-Time System Categorization • Soft systems • Machinery condition monitoring • Man - Machine interfacing • Games • Hard systems • Missile point defense system • Airbag control system • Embedded systems Richard Gharaat, SPSU, Fall 2008

  6. 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. Richard Gharaat, SPSU, Fall 2008

  7. Important Questions • How fast? • How large? Richard Gharaat, SPSU, Fall 2008

  8. Timing And Sequence Issues • The whole point of using STDs is to show how system changes with time. Yet time itself hasn’t 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. Richard Gharaat, SPSU, Fall 2008

  9. Real-Time Data Flow Diagram Richard Gharaat, SPSU, Fall 2008

  10. 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 Richard Gharaat, SPSU, Fall 2008

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