PROFESSIONAL EMBEDDED ARM DEVELOPMENT

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3 PROFESSIONAL EMBEDDED ARM DEVELOPMENT INTRODUCTION xxi PART I ARM SYSTEMS AND DEVELOPMENT CHAPTER 1 The History of ARM CHAPTER 2 ARM Embedded Systems CHAPTER 3 ARM Architecture CHAPTER 4 ARM Assembly Language CHAPTER 5 First Steps CHAPTER 6 Thumb Instruction Set CHAPTER 7 Assembly Instructions CHAPTER 8 NEON CHAPTER 9 Debugging CHAPTER 10 Writing Optimized C PART II REFERENCE APPENDIX A Terminology APPENDIX B ARM Architecture Versions APPENDIX C ARM Core Versions APPENDIX D NEON Intrinsics and Instructions APPENDIX E Assembly Instructions INDEX

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5 PROFESSIONAL Embedded ARM Development

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7 PROFESSIONAL Embedded ARM Development James A. Langbridge

8 Professional Embedded ARM Development Published by John Wiley & Sons, Inc Crosspoint Boulevard Indianapolis, IN Copyright 2014 by John Wiley & Sons, Inc., Indianapolis, Indiana ISBN: ISBN: (ebk) ISBN: (ebk) Manufactured in the United States of America No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) , fax (978) Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) , fax (201) , or online at Limit of Liability/Disclaimer of Warranty: The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation warranties of fitness for a particular purpose. No warranty may be created or extended by sales or promotional materials. The advice and strategies contained herein may not be suitable for every situation. This work is sold with the understanding that the publisher is not engaged in rendering legal, accounting, or other professional services. If professional assistance is required, the services of a competent professional person should be sought. Neither the publisher nor the author shall be liable for damages arising herefrom. The fact that an organization or Web site is referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the organization or Web site may provide or recommendations it may make. Further, readers should be aware that Internet Web sites listed in this work may have changed or disappeared between when this work was written and when it is read. For general information on our other products and services please contact our Customer Care Department within the United States at (877) , outside the United States at (317) or fax (317) Wiley publishes in a variety of print and electronic formats and by print-on-demand. Some material included with standard print versions of this book may not be included in e-books or in print-on-demand. If this book refers to media such as a CD or DVD that is not included in the version you purchased, you may download this material at For more information about Wiley products, visit Trademarks: Wiley, Wrox, the Wrox logo, Wrox Programmer to Programmer, and related trade dress are trademarks or registered trademarks of John Wiley & Sons, Inc. and/or its affiliates, in the United States and other countries, and may not be used without written permission. All other trademarks are the property of their respective owners. John Wiley & Sons, Inc., is not associated with any product or vendor mentioned in this book. ACQUISITIONS EDITOR Mary James PROJECT EDITOR Christina Haviland TECHNICAL EDITORS Jean-Michel Hautbois Chris Shore PRODUCTION EDITOR Christine Mugnolo COPY EDITOR San Dee Phillips EDITORIAL MANAGER Mary Beth Wakefield BUSINESS MANAGER Amy Knies VICE PRESIDENT AND EXECUTIVE GROUP PUBLISHER Richard Swadley ASSOCIATE PUBLISHER Jim Minatel PROJECT COORDINATOR, COVER Patrick Redmond PROOFREADER Nancy Carrasco TECHNICAL PROOFREADER Stephan Cadene INDEXER Robert Swanson COVER DESIGNER Ryan Sneed COVER IMAGE Background: PhotoAlto Images/Fotosearch FREELANCER EDITORIAL MANAGER Rosemarie Graham ASSOCIATE DIRECTOR OF MARKETING David Mayhew MARKETING MANAGER Ashley Zurcher

9 For my loving girlfriend, Anne-Laure, who put up with entire weekends spent on my PC (while she spent her weekend on her laptop, sending me encouraging electronic messages). Thank you for supporting me when I should have been paying attention to you. For my wonderful daughter, Eléna. Thank you for letting daddy work when I really should have spent more time playing with you, and despite what I might have said at the time, thank you for unplugging my computer when I ignored you for too long. Your smiles and first words are what powered me through the late nights and tight deadlines.

10 ABOUT THE AUTHOR JAMES A. LANGBRIDGE does not like talking about himself in the third person, but he will try anyway. James was born in Singapore, and followed his parents to several countries before settling down in Nantes, France, where he lives with his partner and their daughter. James is an embedded systems consultant and has worked for more than 15 years on industrial, military, mobile telephony, and aviation security systems. He works primarily on low-level development, creating bootloaders or optimizing routines in assembly, making the most of small processors. When not on contract, James trains engineers on embedded systems, or he makes new gizmos, much to the dismay of his partner. James wrote his first computer program at age six and has never stopped tinkering since. He began using Apple IIs, ZX80s and ZX81s, before moving on to BBC Micros and the Amiga, before finally having no other option but to use PCs. ABOUT THE TECHNICAL EDITORS CHRIS SHORE is the Training and Education Manager at ARM Ltd, based in Cambridge, UK. He has been responsible for training ARM s global customer base for over 13 years, delivering nearly 200 training courses per year on everything from chip design to software optimization. Chris has taught classes on every continent except Antarctica opportunities there are limited, but surely it s only a matter of time! He is a regular speaker at industry conferences. Following graduation with his degree in Computer Science from Cambridge University, Chris worked as a software consultant for over 15 years, primarily in embedded real-time systems, before moving to ARM in He is a Chartered Engineer and Member of the Institute of Engineering and Technology, and he sits on the Industry Advisory Board of Queen Mary College, London. In his free time he keeps bees, tries to play the guitar, and is always looking for ways to visit new countries. JEAN-MICHEL HAUTBOIS lives in France and has been developing software professionally, or as a hobbyist, for more than 15 years. He is currently employed as an embedded Linux consultant with Vodalys, and is the architect of his company s main video product which was developed on an ARM-based SoC. He is involved in the decision-making process when a new hardware product needs to be created and performance is critical. In his free time Jean-Michel likes to travel, and he enjoys spending time with his wife and newborn son.

11 ACKNOWLEDGMENTS I CAN T FIND THE WORDS to thank everyone who has helped me with this project. It all started with the questions of junior developers; I hope I ve answered your questions. The LinkedIn ARM group has been an excellent source of information, both by the questions asked and the quality of the answers. I would like to thank everyone at ARM who has helped me. My thanks especially to my two technical editors, Chris Shore and Jean-Michel Hautbois; without your help, this book would not have been possible. My thanks also to Philippe Lançon for your support, to Atmel and Silicon Labs for your boards and your time, and to all my friends and family who helped me with this project. And, of course, the Wiley team, who helped me every time I had a question or a doubt, and who put up with me. To Christina Haviland, Mary James, San Dee Phillips, and everyone else who helped me thank you.

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13 CONTENTS INTRODUCTION xxi PART I: ARM SYSTEMS AND DEVELOPMENT CHAPTER 1: THE HISTORY OF ARM 3 The Origin of ARM 3 Why Acorn Decided to Create a New Processor 5 Why Acorn Became ARM 5 Why ARM Doesn t Actually Produce Microprocessors 6 ARM Naming Conventions 7 How to Tell What Processor You Are Dealing With 8 Differences between ARM7TDMI and ARM926EJ-S 9 Differences between ARM7 and ARMv7 10 Differences between Cortex-M and Cortex-A 11 Manufacturer Documentation 11 What Is ARM Doing Today? 11 Summary 12 CHAPTER 2: ARM EMBEDDED SYSTEMS 13 ARM Embedded Systems Defined 15 What Is a System on Chip? 15 What s the Difference between Embedded Systems and System Programming? 16 Why Is Optimization So Important? 17 What Is the Advantage of a RISC Architecture? 19 Choosing the Right Processor 21 What Should You Start With? 22 What Boards Are Available? 23 What Operating Systems Exist? 24 Which Compiler Is Best Suited to My Purpose? 25 Getting Ready for Debugging 26 Are There Any Complete Development Environments? 26 Is There Anything Else I Need to Know? 27 Summary 28

14 CONTENTS CHAPTER 3: ARM ARCHITECTURE 29 Understanding the Basics 29 Register 30 Stack 31 Internal RAM 31 Cache 31 Getting to Know the Different ARM Subsystems 33 Presenting the Processor Registers 33 Presenting the CPSR 35 Calculation Unit 37 Pipeline 37 Tightly Coupled Memory 39 Coprocessors 39 Understanding the Different Concepts 40 What Is an Exception? 40 Handling Different Exceptions 42 Modes of Operation 43 Vector Table 44 Memory Management 45 Presenting Different Technologies 47 JTAG Debug (D) 47 Enhanced DSP (E) 47 Vector Floating Point (F) 48 EmbeddedICE (I) 48 Jazelle (J) 48 Long Multiply (M) 48 Thumb (T) 49 Synthesizable (S) 49 TrustZone 49 NEON 50 big.little 50 Summary 51 CHAPTER 4: ARM ASSEMBLY LANGUAGE 53 Introduction to Assembly Language 53 Talking to a Computer 54 Why Learn Assembly? 55 Speed 55 Size 56 Fun! 57 Compilers Aren t Perfect 57 xii

15 CONTENTS Understanding Computer Science through Assembly 58 Shouldn t You Just Write in Assembly? 58 Uses of Assembly 59 Writing Bootloaders 59 Reverse Engineering 59 Optimization 60 ARM Assembly Language 60 Layout 61 Instruction Format 61 Condition Codes 62 Updating Condition Flags 65 Addressing Modes 66 ARM Assembly Primer 69 Loading and Storing 69 Setting Values 69 Branching 69 Mathematics 70 Understanding an Example Program 70 Summary 71 CHAPTER 5: FIRST STEPS 73 Hello World! 74 Taking the World Apart 77 Hello World, for Real This Time! 79 Software Implementation 81 Memory Mapping 83 Real World Examples 85 Silicon Labs STK Silicon Labs STK Atmel D20 Xplained Pro 95 Case Study: U-Boot 102 Machine Study: Raspberry Pi 103 Boot Procedure 103 Compiling Programs for the Raspberry Pi 104 What s Next? 105 Summary 105 CHAPTER 6: THUMB INSTRUCTION SET 107 Thumb 108 Thumb-2 Technology 109 How Thumb Is Executed 109 xiii