Introduction

The title of the last chapter included the phrase, "Real Time". The term, Real Time, is used to describe a computing system that must meet deadlines. We did not define this term in Chapter 7, Real-Time Signal Processing because, in the context of handling audio samples, an implicit deadline is the sampling rate. However, you may recall that our ISR illuminated an error LED if the main super loop did not output the previous sample before a new sample arrived.

The audio application is an example of a soft deadline. It wouldn't be a catastrophe if the system missed this deadline once or twice; the audio quality would suffer, but this may go unnoticed. Contrast this with other applications, such as an embedded system used in fly-by-wire avionic applications, medical equipment, or a nuclear reactor. In these cases, missing a deadline could be catastrophic and result in death. Deadlines in these cases are known as hard deadlines and, in order to meet safety standards, designers need...