by Alan C. Shaw
Real-time systems are those that must perform computations by specific times -- late results are considered incorrect. In a weak way, all computations are real-time: for example, if your PC took a year to respond to a keystroke, it would not be considered to be operating correctly. Systems that are strongly real-time have very specific time constraints that are generally imposed on them by requirements in the physical world. For example, if the avionics system on a computer-controlled aircraft fails to update the positions of the control surfaces many times per second, the aircraft can become unstable or even break up in the air. When designing and implementing the control software for this type of aircraft it may be extremely difficult to guarantee that all real-time constraints will be met under all conditions.
The purpose of Real-Time Systems and Software is not to describe how real-time systems are currently built in practice. Rather, it provides an overview of academic research in real-time systems, where the goal has been to help create real-time software that is guaranteed to be correct, while minimizing hardware costs and development effort. This distinction is important because a lot of the work that Shaw describes is not particularly practical at the moment, and a lot of it may never be.
Does the book accomplish its goals? Well, that depends. It is good in that it covers quite a wide range of material including often-neglected topics such as determination of worst-case execution time. It is less than good in the sense that at only two hundred pages, it is too short to provide more than a brief introduction to each topic and some pointers to the original sources. Unfortunately, quite a few of the references in the text cannot be found in the bibliography: an inexcusable oversight in a book of this type. Otherwise, this is a pretty good book and it should be useful as background reading for professionals and academics, or as a textbook in a class about real-time systems.
copyright © 2001 John Regehr