Embedded Systems Design: An Introduction to Processes, Tools, and Techniques
An easy-to-understand guidebook for those embarking upon an embedded processor development project.
TABLE OF CONTENTS Embedded Systems Design: An Introduction to Processes, Tools, and Techniques
Chapter 5: Special Software Techniques
Chapter 4 looked at how the embedded systems software-development process differs from typical application development. This chapter introduces several programming techniques that belong in every embedded systems programmer s toolset. The chapter begins with a discussion of how to manipulate hardware directly from C, then discusses some algorithms that aren t seen outside the embedded domain, and closes with a pointer toward a portion of the Unified Modeling Language (UML) that has special significance for embedded systems programmers.
Manipulating the Hardware
Embedded systems programmers often need to write code that directly manipulates some peripheral device. Depending on your architecture, the device might be either port mapped or memory mapped. If your architecture supports a separate I/O address space and the device is port mapped, you have no choice but to drop down to assembly to perform the actual manipulation; this is because C has no intrinsic notion of ports. Some C compilers provide special CPU-specific intrinsic functions, which are replaced at translation time by CPU-specific assembly language operations. While still machine-specific, intrinsic functions do allow the programmer to avoid in-line assembly. Things are much simpler if the device is memory mapped.
In-line Assembly
If you only need to read or write from a particular port, in-line assembly is probably the easiest solution. In-line assembly is always extremely compiler dependent. Some vendors use a #pragma directive to escape the assembly instructions, some use special symbols such as _asm/_endasm, and some wrap the assembly in what looks like a function call.
asm(...
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