5.1 Introduction

In this chapter we study in detail the process of creating programs for embedded processors. The creation of embedded programs is at the heart of embedded system design. If you are reading this book, you almost certainly have an understanding of programming, but designing and implementing embedded programs is different and more challenging than writing typical workstation or PC programs. Embedded code must not only provide rich functionality, it must also often run at a required rate to meet system deadlines, fit into the allowed amount of memory, and meet power consumption requirements. Designing code that simultaneously meets multiple design constraints is a considerable challenge, but luckily there are techniques and tools that we can use to help us through the design process. Making sure that the program works is also a challenge, but once again methods and tools come to our aid.

Throughout the discussion we concentrate on high-level programming languages, specifically C. High-level languages were once shunned as too inefficient for embedded microcontrollers, but better compilers, more compiler-friendly architectures, and faster processors and memory have made high-level language programs common. Some sections of a program may still need to be written in assembly language if the compiler doesn’t give sufficiently good results, but even when coding in assembly language it is often helpful to think about the program’s functionality in high-level form. Many of the analysis and optimization techniques that we study in this chapter are equally applicable to programs written in assembly language.

The next section talks about some software components that are commonly used in embedded software. Section 5.3 introduces the control/data flow graph as a model for high-level language programs (which can also be applied to programs written originally in assembly language). Section 5.4 reviews the assembly and linking process while Section 5.5 introduces some compilation techniques. Section 5.6 introduces methods for analyzing the performance of programs. We talk about optimization techniques specific to embedded computing in the next three sections: performance in Section 5.7, energy consumption in Section 5.8, and size in Section 5.9. In Section 5.10, we discuss techniques for ensuring that the programs you write are correct. We close with two design examples: a software modem as a design example in Section 5.11 and a digital still camera in Section 5.12.