Professional Embedded ARM Development

Chapter 4

ARM Assembly Language

WHAT’S IN THIS CHAPTER?

• Introduction to ARM assembly
• Use of assembly
• Understanding condition codes
• Understanding addressing modes
• Understanding your first ARM assembly program

Assembly language is the most basic programming language available for any processor. It is a collection of commands, or instructions, that the processor can execute. A program is a list of instructions in a specific order telling the computer what to do. Just like a calculator, you can tell a processor to take a number, to multiply it by 2, and to give you the answer. However, you need to supply some more information; you need to tell the processor where to get the number and what to do with it afterward.

INTRODUCTION TO ASSEMBLY LANGUAGE

A processor runs machine code, and machine code can be specific from one processor to another. Machine code written for a 6502 cannot, and will not, run on a 68000. Machine code is a list of numbers that make no sense whatsoever to (most) humans. To make the programmer’s life a little more bearable, Assembly language was invented. Assembly language consists of words and numbers, and although it isn’t as easy to understand as the English language, it is much easier to understand than reading numbers or punch cards.

Assembly language enables programmers to write computer programs, telling the processor exactly what it must do.

TALKING TO A COMPUTER

Talking to a computer isn’t as easy as you would think. Hollywood has made a good job of making ...