C is a relatively "low level" language. This characterization is not pejorative; it simply means that C deals with the same sort of objects that most computers do. These may be combined and moved about with the arithmetic and logical operators implemented by real machines.
1.3.1 Other Embedded Languages
mentioning in greater detail.
In the early days, embedded software was written exclusively in the assembly language of the target processor. This gave programmers complete control of the processor and other hardware, but at a price. Assembly languages have many disadvantages, not the least of which are higher software development costs and a lack of code portability. In addition, finding skilled assembly programmers has become much more difficult in recent years. Assembly is now used primarily as an adjunct to the high-level language, usually only for those small pieces of code that must be extremely efficient or ultra-compact, or cannot be written in any other way.
C++ is an object-oriented superset of C that is increasingly popular among embedded programmers. All of the core language features are the same as C, but C++ adds new functionality for better data abstraction and a more object-oriented style of programming. These new features are very helpful to software developers, but some of them do reduce the efficiency of the executable program. So C++ tends to be most popular with large development teams, where the benefits to developers outweigh the loss of program efficiency.
Ada is also an object-oriented language, though it is substantially different than C++. Ada was originally designed by the U.S. Department of Defense for the development of mission-critical military software. Despite being twice accepted as an international standard (Ada83 and Ada95), it has not gained much of a foothold outside of the defense and aerospace industries. And it is losing ground there in recent years. This is unfortunate because the Ada language has many features that would simplify embedded software development if used instead of C++.
1.3.2 Choosing a Language for the Book
Certainly, C must be the centerpiece of any book about embedded programming and this book will be no exception. More than half of the sample code is written in C, and the discussion will focus primarily on C-related programming issues. Of course, everything that is said about C programming applies equally to C++. In addition, I will cover those features of C++ that are most useful for embedded software development and use them in the later examples. Assembly language will be discussed in certain limited contexts, but will be avoided whenever possible. In other words, I will mention assembly language only when a particular programming task cannot be accomplished in any other way.
I feel that this mixed treatment of C, C++, and assembly most accurately reflects how embedded software is actually developed today and how it will continue to be developed in the near-term future. I hope that this choice will keep the discussion clear, provide information that is useful to people developing actual systems, and include as large a potential audience as possible.
1.4 A Few Words About Hardware
Even selecting a standard embedded platform is difficult. As you have already learned, there is no such thing as a "typical" embedded system. Whatever hardware is selected, the majority of readers will not have access to it. But despite this rather significant problem, I do feel it is important to select a reference hardware platform for use in the examples. In so doing, I hope to make the examples consistent and, thus, the entire discussion more clear.
In order to illustrate as many points as possible with a single piece of hardware, I have found it necessary to select a middle-of-the-road platform. This hardware consists of a 16-bit processor (Intel's 80188EB),
a decent amount of memory (128KB of RAM and 256 KB of ROM), and some common types of inputs, outputs, and peripheral components. The board I've chosen is called the Target188EB and is manufactured and sold by Arcom Control Systems. More information about the Arcom board and instructions for obtaining one can be found in Appendix A.
If you have access to the reference hardware, you will be able to work through the examples in the book exactly as they are presented. Otherwise, you will need to port the example code to an embedded platform that you do have access to. Toward that end, every effort has been made to make the example programs as portable as possible. However, the reader should bear in mind that the hardware in each embedded system is different and that some of the examples might be meaningless on his hardware. For example, it wouldn't make sense to port the Flash memory driver presented in Chapter 6 to a board that had no Flash memory devices.