Classification of Events in Real-time System
Last Updated : 09 May, 2025
Events in a real-time System are the actions or the result of the actions that are generated by the system or the environment. An event in a real-tie system is either a instantaneous or may have certain duration. The classification of events in a real-time system is based on different theories. Once the events in real-time system are classified then timing constraints are categorized accordingly.
Classification of Events
1. On the Basis of Timing Urgency
Hard Real-Time Events: These events must be completed within strict deadlines. Missing a deadline can lead to catastrophic failure or system breakdown. Such events are critical for the system's correct functioning, and they cannot tolerate any delays.
Examples: Safety-critical systems like airbags in cars or medical devices.
Hard real-time eventsSoft Real-Time Events: These events must be completed in a timely manner, but missing the deadline occasionally does not result in system failure. However, the performance of the system can degrade if deadlines are frequently missed.
Examples: Video streaming applications or online gaming, where occasional delays may affect the quality but not the overall functionality.
Soft real-time eventsFirm Real-Time Events: These events must be completed within their deadlines, but missing a deadline does not result in catastrophic failure. However, missing deadlines too often results in significant performance degradation. Firm real-time events balance between hard and soft real-time systems.
Example: A stock trading system where timely processing is critical, but occasional deadline misses may not lead to complete failure.
Firm real-time events2. On the Basis of Arrival Pattern
Periodic Events: These events occur at regular, predictable intervals. The system knows exactly when the event will occur, and it has a fixed periodicity.
Example: Sensor readings that occur every second or clock ticks in embedded systems.
Periodic EventsAperiodic Events: These events occur at unpredictable times without any specific regularity or fixed intervals. The timing of these events is unknown until they happen.
Example: User input or external triggers like incoming network requests.
Aperiodic EventsSporadic Events: These are similar to aperiodic events, but they have a known minimum inter-arrival time between occurrences. Although the exact arrival times are not predictable, they are spaced apart by at least a defined interval.
Example: A network packet arriving sporadically but at least 10 milliseconds apart.
Sporadic Events3. On the Basis of Duration
An event in a real-time system may be instantaneous or may have some duration. On this basis events in a real-time system are classified into two categories:
Instantaneous Events: In a real-time system, instantaneous events are the events having duration time zero. These events may be generated by the environment or the computer system but these are generated at instant time. Instantaneous events may be stimulus events or response events. Example :
- Pressing a key at a instant.
- Display of alert notice at any instant.
Durational Events: In a real-time system, duration events are the events having duration time greater than zero. These events may be generated by the environment or the computer system but these events have some duration time. Duration events may be stimulus events or response events. Example :
- Measuring of temperature is a durational event.
- All the computational events inside computer system are durational events.
4. On the Basis of Response
An event in a real-time system may be generated by either system of the environment. On this basis events are classified into two categories:
Stimulus Events: In a real-time system, stimulus events are generated by the environment. Stimulus events act on the computer system. Stimulus events are aperiodic and asynchronous. These events are not generated for a response. Stimulus events may be instantaneous or may have some duration. Example :
- Typing on keyboard is a stimulus event that acts on the computer system.
- Measuring of temperature in a plant.
Response Events: In a real-time system, response events are generated by the computer system. These events act on the environment. These events are generated in response of stimulus events. Response events may be periodic or aperiodic. These events are generated for a response. Response events are generally instantaneous events. Example :
- Alarm ringing at 4 o’clock is a response event.
- Switching off the induction at temperature exceeding 100 degree.
5. On the Basis of Criticality
Critical Events: These events are essential for the system's core functionality and failure to process them in time can result in significant consequences, including system failure, loss of critical data, or safety hazards. Example:
- Real-time monitoring systems
- Medical devices
- Flight control systems
Non-Critical Events: These events are not essential for the core functionality of the system and can tolerate delays or even be missed without causing significant problems. Non-critical events often relate to background tasks or low-priority operations. Example:
- Data backups
- Routine maintenance tasks.
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