May 10th, 2019 by
Real time systems are designed to respond to real events within a bounded time frame and before measurable deadlines. However, they are also designed to uphold precision. This means that the measurable speed of a system report to an event is as crucial as the system’s ability to respond to real time events at the right moment in time. To guarantee this, a high resolution timer that preforms actions within precise durations may be used. As such, a real time system can be defined using it acceptable behavior; ability to react to events before their given deadline and ability to accurately execute periodic processes despite the overall system work load.
In real time systems, deadlines can be relative whereby, the system is required to respond to a message or event within a predetermined period after receiving the message or confirming the event. The elevator is a good example of relative deadline in a real time system. As the elevator passes through the sensor notifying it that it should stop at the next floor, the elevator’s real time software must respond to the notification within milliseconds others, the elevator will not stop at the marked floor.
Relative deadline is the amount of time within which a system must respond upon receiving a request. Absolute deadline is the precise time that a task should complete regardless of its start time or request arrival. Absolute deadlines are mainly applied where real time system checks are conducted on regular intervals. A good example is the aircraft control system from which critical flight data such as; core temperature and altitude is polled continuously. Failure to monitor such information variables at precise time durations can cause entire aircraft system problems with potential to cause catastrophic disasters.
However, regardless of whether relative or absolute deadline is in use, time remains a core real time system component that ensure proper system operations. The elevator sensor should know and react to floor sensors within a predetermined deadline in order to guarantee proper system operations. Similarly, a flight control system must move at the precise time in reaction to recent and accurate data sets to guarantee safe flights.
Real time systems must strictly adhere to end to end deadlines. For example, if a system is required to send a request response within a millisecond but does so in 500 microseconds, the system requirement may be met. However, should the system request experience delays, the required response will not be sent within the specified time of one millisecond given that, the time requirement starts when the request is sent.
In real time systems, time delays from when a real event take place to the time system codes process the event must be bounded. The ability to meets real time deadlines should by guaranteed and predictable always to provide the amount of determinism required for each real time system to operate effectively.