1.2 Real-Time Embedded Systems
In the simplest form, real-time systems can be defined as those systems that respond to external events in a timely fashion, as shown in Figure 1.5. The response time is guaranteed. We revisit this definition after presenting some examples of real-time systems.
Figure 1.5: A simple view of real-time systems.
External events can have synchronous or asynchronous characteristics. Responding to external events includes recognizing when an event occurs, performing the required processing as a result of the event, and outputting the necessary results within a given time constraint. Timing constraints include finish time, or both start time and finish time.
A good way to understand the relationship between real-time systems and embedded systems is to view them as two intersecting circles, as shown in Figure 1.6. It can be seen that not all embedded systems exhibit real-time behaviors nor are all real-time systems embedded. However, the two systems are not mutually exclusive, and the area in which they overlap creates the combination of systems known as real-time embedded systems.
Figure 1.6: Real-time embedded systems.
Knowing this fact and because we have covered the various aspects of embedded systems in the previous sections, we can now focus our attention on real-time systems.
Figure 1.7: Structure of real-time systems.