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Introduction to real time software systems script


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Introduces real-time software systems and discusses differences between these and other types of system. Accompanies video at:

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Introduction to real time software systems script

  1. 1. Real-time Software Engineering Software Engineering 10
  2. 2. Computers are used to control a wide range of systems from simple domestic machines, through games controllers, to entire manufacturing plants.
  3. 3. The software in these systems is embedded in system hardware, often in read-only memory, and usually responds, in real time, to events from the system’s environment.
  4. 4. Their software must react to events generated by the hardware and, often, issue control signals in response to these events.
  5. 5. Responsiveness in real-time is the critical difference between embedded systems and other software systems, such as web- based systems or personal software systems.
  6. 6. In a real-time system, the correctness depends both on the response to an input and the time taken to generate that response.
  7. 7. If the response to a stimulus in a real-time system is too late, the system is considered to be incorrect.
  8. 8. A real-time system is a software system where the correct functioning of the system depends on the results produced by the system and the time at which these results are produced.
  9. 9. A soft real-time system is a system whose operation is degraded if results are not produced according to the specified timing requirements.
  10. 10. A hard real-time system is a system whose operation is incorrect if results are not produced according to the timing specification.
  11. 11. Embedded systems generally run continuously. They start when the system is powered up and do not terminate until the power is switched off.
  12. 12. Interactions with the system’s environment are unpredictable. Events may not occur when expected.
  13. 13. There may be physical limitations, such as battery power, that affect the design of a system.
  14. 14. Real-time systems often interact directly with hardware through specialized hardware interfaces.
  15. 15. Issues of safety and reliability may may be the most important factors to be considered when designing the system.
  16. 16. Real-time systems are often considered to be reactive systems. Given a stimulus, the system must produce a reaction or response within a specified time.
  17. 17. Periodic stimuli. Stimuli which occur at predictable time intervals A sensor may return a value every 250 milliseconds. The system response depends on that value.
  18. 18. Aperiodic stimuli. Stimuli which occur at unpredictable times For example, it is impossible to know when a power failure will occur.
  19. 19. A general model of an embedded real- time system 04/12/2014 19
  20. 20. Real-time systems are usually organised as a number of parallel processes.
  21. 21. This allows them to respond in a timely way to events from the system’s environment.
  22. 22. It is difficult to design a sequential process in such a way that you can guarantee that predict the responsiveness of the system.
  23. 23. Sensor and actuator processes 04/12/2014 23