![](https://csdnimg.cn/release/download_crawler_static/10764122/bg12.jpg)
Introduction
ARM DEN0024A Copyright © 2015 ARM. All rights reserved. 1-3
ID050815 Non-Confidential
1.1 How to use this book
This book provides a single guide for programmers who want to use the Cortex-A series
processors that implement the ARMv8 architecture. The guide brings together information from
a wide variety of sources that is useful to both ARM assembly language and C programmers. It
is meant to complement rather than replace other ARM documentation available for ARMv8
processors. The other documents for specific information includes the ARM Technical
Reference Manuals (TRMs) for the processors themselves, documentation for individual
devices or boards or, most importantly, the ARM Architecture Reference Manual - ARMv8, for
ARMv8-A architecture profile - the ARM ARM.
This book is not written at an introductory level. It assumes some knowledge of the C
programming language and microprocessors. Hardware concepts such as caches and Memory
Management Units are covered, but only where this knowledge is valuable to the application
writer. The book looks at the way operating systems utilize ARMv8 features, and how to take
full advantage of the capabilities of the ARMv8 processors. Some chapters contain pointers to
additional reading. We also refer to books and web sites that can give a deeper level of
background to the subject matter, but often the main focus is the ARM-specific detail. No
assumptions are made on the use of any particular toolchain, and both GNU and ARM tools are
mentioned throughout the book.
If you are new to the ARMv8 architecture, Chapter 2 ARMv8-A Architecture and Processors
describes the previous 32-bit ARM architectures, introduces ARMv8, and describes some of the
properties of the ARMv8 processors. Next, Chapter 3 Fundamentals of ARMv8 describes the
building blocks of the architecture in the form of Exception levels and Execution states.
Chapter 4 ARMv8 Registers then describes the registers available to you in the ARMv8
architecture.
One of the most significant changes introduced in the ARMv8 architecture is the addition of a
64-bit instruction set, which complements the existing 32-bit architecture. Chapter 5 An
Introduction to the ARMv8 Instruction Sets describes the differences between the Instruction Set
Architecture (ISA) of ARMv7 (A32), and that of the A64 instruction set. Chapter 6 The A64
instruction set looks at the Instruction Set and its use in more detail. In addition to a new
instruction set for general operation, ARMv8 also has a changed NEON and floating-point
instruction set. Chapter 7 AArch64 Floating-point and NEON describes the changes in ARMv8
to ARM Advanced SIMD (NEON) and floating-point instructions. For a more detailed guide to
NEON and its capabilities at ARMv7, refer to the ARM
®
NEON
™
Programmer’s Guide.
Chapter 8 Porting to A64 of this book covers the problems you might encounter when porting
code from other architectures, or previous ARM architectures to ARMv8. Chapter 9 The ABI
for ARM 64-bit Architecture describes the Application Binary Interface (ABI) for the ARM
architecture specification. The ABI is a specification for all the programming behavior of an
ARM target, which governs the form your 64-bit code takes. Chapter 10 AArch64 Exception
Handling describes the exception handling behavior of ARMv8 in AArch64 state.
Following this, the focus moves to the internal architecture of the processor. Chapter 11 Caches
describes the design of caches and how the use of caches can improve performance.
An important motivating factor behind ARMv8 and moving to a 64-bit architecture is
potentially enabling access to larger address space than is possible using just 32 bits. Chapter 12
The Memory Management Unit describes how the MMU converts virtual memory addresses to
physical addresses.
Chapter 13 Memory Ordering describes the weakly-ordered model of memory in the ARMv8
architecture. Generally, this means that the order of memory accesses is not required to be the
same as the program order for load and store operations. Only some programmers must be aware
of memory ordering issues. If your code interacts directly with the hardware or with code