Classification of Events in Real-time System

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 thereafter timing constraints are categorized accordingly.

Classification of Events :

1. On the basis of generation :
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 :

  1. Typing on keyboard is a stimulus event that acts on the computer system.
  2. 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 :

  1. Alarm ringing at 4 o’clock is a response event.
  2. Switching off the induction at temperature exceeding 100 degree.

2. 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 :

  1. Pressing a key at a instant.
  2. 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 :

  1. Measuring of temperature is a durational event.
  2. All the computational events inside computer system are durational events.