Professional Embedded ARM Development

Chapter 7

Assembly Instructions

WHAT’S IN THIS CHAPTER?

• Different assembly instructions
• Assembly arithmetic
• Different branch instructions
• Use of assembly instructions

Assembly is just like any other computer language; you must first know the basics: the syntax of the language. After you know how to speak assembly, then comes the interesting part — vocabulary.

ARM cores follow a Reduced Instruction Set Computing (RISC) design philosophy. They have fewer instructions than CISC counterparts, but each individual instruction, being simpler, is also faster. Just like a box of Legos, it is possible to make amazing sculptures with simple pieces. Learning ARM Assembly is the same; after you grasp the power of each simple instruction, it becomes easy to read and write programs.

Because most ARM cores now support two instruction sets, ARM and Thumb, ARM created the Unified Assembler Language (UAL) to write programs for both languages. The following chapter is written in UAL, and as such, the instruction format should be supported by all the modern compilers and environments.

ARM assembly instructions have gone through different versions, as architectures have added more and more instructions. Some cores may have more instructions due to its architecture; for more information, consult the manufacturer’s documentation. This documentation will contain the ARM Architecture version. ARM’s documentation will list all the instructions available.

MOVEMENT

Movement instructions are used to transfer ...