Introductory Lecture

19th January 2010

These are lecture notes from my Computer Science course, not a general reference for "Introductory Lecture"

Terminology

• 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.

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