Introductory Lecture

These are lecture notes from my Computer Science course. For learning about real-time systems, I recommend Real-Time Systems and Programming Languages.


  • Hard real-time: Systems where it is imperative that responses occur within the required deadline, e.g. a flight control system
  • Soft real-time: Systems where it would be useful to know the data immediately, but the data can still be useful after deadlines (degrading)
  • Firm real-time: Similar to hard real-time. Soft real-time but there’s no benefit to late delivery. Different to hard real-time in that in hard real-time old data has a negative use, with firm real-time it just has zero use.

  • Time-aware: System that makes an explicit reference to time
  • Reactive: Control systems, systems that must react (produce output) within deadline based on input. Subject to jitter – variability in input/output read/write.

  • Time-triggered: computation is triggered by passage of time, e.g. a periodic activity. Polling
  • Event-triggered: Javascript. A sporadic activity is where there is a bound on the arrival interval of the event (no two interrupts within a period). An aperiodic activity is when intervals could be made at any time. This is important because might need to know about load on processor.
This entry was posted in lecture, rts. Bookmark the permalink.