Rapid development of reliable embedded systems

At TTE Systems, we receive many enquiries from people who want to learn how to program embedded systems. The questions come from professional programmers (particularly those who are considering a career change from “desktop” to “embedded” systems) as well as from students and hobbyists.

In many cases, the people concerned have limited funds available.

In response to these questions, we’ve created this webpage. On this page, we provide a “10-step guide” for people who want to learn how to program embedded systems. Our focus is on ways in which people can learn how to create reliable systems.

1. Learn how to program in C for a “desktop” computer

Before you can start to program embedded systems, you need to learn how to program. While it is not impossible to begin programming using an embedded board, most people find it much easier to learn how to program on a desktop computer before they start to deal with the complexities of cross-compilation, debugging over a JTAG link, etc.

We therefore recommend that you learn how to program a desktop computer, in C, before you start trying to program an embedded processor.

To explain why we recommend learning C, we make the following observations:

• Computers (such as microcontroller, microprocessor or DSP chips) only accept instructions in “machine code” (“object code”).
• Machine code is, by definition, in the language of the computer, rather than that of the programmer. Interpretation of the code by the programmer is difficult and error prone.
• All software, whether in assembly, C, C++, Java or Ada must ultimately be translated into machine code in order to be executed by the computer.
• There is no point in creating ‘perfect’ source code, if we then make use of a poor translator program (such as an assembler or compiler) and thereby generate executable code that does not operate as we intended.
• When compared to “desktop” processors, embedded processors tend to have limited processor power and very limited memory available: the language used must be efficient.
• To program embedded systems, we need low-level access to the hardware: this means, at least, being able to read from and write to particular memory locations (using ‘pointers’ or an equivalent mechanism).

Of course, not all of the issues involved in language selection are purely technical:

• No software company remains in business for very long if it generates new code, from scratch, for every project. The language used must support the creation of flexible libraries, making it easy to re-use (well-tested) code components in a range of projects. It must also be possible to adapt complete code systems to work with a new or updated processor with minimal difficulty.
• Staff members change and existing personnel have limited memory spans. At the same time, systems evolve and processors are updated. Many embedded systems have a long lifespan. During this time, their code will often have to be maintained. Good code must therefore be easy to understand now, and in five years time (and not just by those who first wrote it).
• The language chosen should be in common use. This will ensure that you can continue to recruit experienced developers who have knowledge of the language. It will also mean that your existing developers will have access to sources of information (such as books, training courses, WWW sites) which give examples of good design and programming practice.

Even this short list immediately raises the paradox of programming language selection. From one point of view, only machine code is safe, since every other language involves a translator, and any code you create is only as safe as the code written by the manufacturers of the translator. On the other hand, real code needs to be maintained and re-used in new projects, possibly on different hardware: few people would argue that machine code is easy to understand, debug or to port.

Inevitably, therefore, we need to make compromises; there is no perfect solution. All we can really say is that we require a language that is efficient, high-level, gives low-level access to hardware, and is well defined. In addition - of course - the language must be available for the platforms we wish to use. Against all of these points, C scores well.

We can summarise C’s features as follows:

• It is a ‘mid-level’ language, with ‘high-level’ features (such as support for functions and modules), and ‘low-level’ features (such as good access to hardware via pointers);
• It is very efficient;
• It is popular and well understood;
• Even desktop developers who have used only Java or C++ can soon understand C syntax;
• Good, well-proven compilers are available for every embedded processor (8-bit to 32-bit or more);
• Experienced staff are available;
• Books, training courses, code samples and WWW sites discussing the use of the language are all widely available.

Overall, C’s strengths for embedded system development greatly outweigh its weakness. It may not be an ideal language for developing embedded systems, but is unlikely that a perfect language will ever be created.

2. Learn the basics of “embedded C”

When you are familiar with desktop C, we suggest that you begin to explore embedded systems using a simple processor. For example, the 8051 microcontroller is a popular “starter” processor which is still used in many “real” systems.

If you decide to start with the 8051 microcontroller, “Embedded C” provides a gentle introduction to the programming of embedded systems (using 8051 microcontrollers). Please note that Embedded C is a self-contained “teach yourself” program: the package includes both a compiler and processor simulator (on CD), which means that you can run all of the examples in the book (and learn a great deal about the programming of embedded systems in C) without buying — or building — any hardware.

Please note that two Chinese translations of “EC” are available (one for Taiwan, one for mainland China).

• Pont, M.J. (2002) “Embedded C”, Addison-Wesley. ISBN: 0-201-79523-X.
• Pont, M.J. (2003) “Embedded C”, Chinese Electric Power Press. ISBN: 7-5083-1814-5.
• Pont, M.J. (2004) “Embedded C”, Pearson Education Taiwan. ISBN: 986-7491-52-1.