Real-Time Systems
Use this page to revise what "real-time" means — it is about meeting deadlines, not about being fast in general.
Hard, firm, and soft
- Hard real-time: a missed deadline is a system failure (airbag, some motor commutation).
- Firm: a late result is useless but the system can continue (some control samples).
- Soft: late is degraded quality (UI animation, best-effort telemetry).
Latency, jitter, deadline
- Latency is the delay from event to response. Jitter is variation in that delay. A deadline is the latest acceptable completion time.
- Worst-case timing matters more than average timing on a microcontroller.
Scheduling ideas
A super-loop runs tasks in sequence; an interrupt preempts for an event; an RTOS schedules tasks by priority. Blocking (delay, waiting on I/O) in the wrong place is a typical way to miss a deadline.
Starting Points
- Liu, J. W. S. Real-Time Systems. Prentice Hall (concepts: deadline, latency).
- Real-time & constraint analysis
- Operating systems & RTOS
Key Points
- You can distinguish hard, firm, and soft real-time with an embedded example of each.
- You can define latency, jitter, and deadline in plain language.
- You can explain why worst-case time matters on an MCU.
- You can contrast super-loop, interrupts, and an RTOS at a conceptual level.