Glossary · Automation software engineering and architecture
Deadline (real-time)
Also known as: Deadline, Timing deadline
German: Ausführungsfrist
In real-time systems, a deadline is the latest point in time by which a task, job or response must be completed after its release or triggering event for the result to be correct or useful. Whether missing a deadline is a failure, a degradation or tolerable defines hard, firm and soft real time.
- Software engineering
In one sentence
A deadline is the latest time by which a real-time task or response must be completed for its result to be correct or useful.
Example
The position controller must finish its calculation within 250 µs of the cycle start; missing this deadline triggers a drive fault.
How it applies
- Engineering: Deadlines are derived from process requirements, such as control loop stability, reaction times or communication cycles. Worst-case execution times must be analyzed or measured to show that deadlines are met under all conditions.
- Operation: Controllers typically monitor deadlines with watchdogs or cycle time monitoring and react to overruns with a defined fault reaction. Overruns often appear after software extensions or when diagnostics are switched on.
- Documentation: Document the deadline of each time-critical task, how it is monitored and what happens when it is missed. Service documentation should explain cycle time overrun alarms and their typical causes.
Deadline vs. latency
A deadline is a requirement; Latency is the measured delay. A system meets its deadlines if its worst-case latency stays below them. For safety functions, the relevant timing requirement is expressed as a response time within the overall Protective response time, which includes sensors, logic and actuators.