Here, we will cover both the original 32-bit and the newer 64-bit architectures. There were multiple versions released over time, starting from the ARMv1. In this book, we will focus on the recent versions of them.
ARM is a load-store architecture; it divides all instructions into the following two categories:
- Memory access: Moves data between memory and registers
- Arithmetic Logic Unit (ALU) operations: Does computations involving registers
ARM supports arithmetic operations for adding, subtracting, and multiplying, and some new versions, starting from ARMv7, also support division operations. It supports big-endian order, and uses the little-endian format by default.
There are 16 registers visible at any time on the 32-bit ARM: R0-R15. This number is convenient as it takes only 4 bits to define which register is going to be used. Out of them, 13 (sometimes referred to as 14, including R14 , or 15, also including R13) are general-purpose registers: R13 and R15 each have a special...
