Embedded Linux Primer, Second Edition

Transcription

1 Toronto Montreal Boston Paris Embedded Linux Primer, Second Edition A Practical, Real-World Approach Christopher Hallinan PRENTICE HALL Prentice Hall Professional Technical Reference Upper Saddle River, New York - Capetown Sydney NJ Tokyo Indianapolis San Francisco London Munich Singapore Mexico City Madrid

2 Contents Foreword for the First Edition Foreword for the Second Edition Preface Acknowledgments for the First Edition Acknowledgments for the Second Edition About the Author xxv xxvi xxvii xxxiii xxxv xxxvi Chapter 1 Introduction Why Linux? Embedded Linux Today Open Source and the GPL Free Versus Freedom Standards and Relevant Bodies Linux Standard Base Linux Foundation Carrier-Grade Linux Mobile Linux Initiative: Moblin Service Availability Forum Summary Suggestions for Additional Reading 8 VII

3 viii Embedded Linux Primer, Second Edirion Chapter 2 The Big Picture Embedded or Not? BIOS Versus Bootloader Anatomy of an Embedded System Typical Embedded Linux Setup Starting the Target Board Booting the Kernel Kernel Initialization: Overview First User Space Process: init Storage Considerations Flash Memory NAND Flash Flash Usage Flash File Systems Memory Space Execution Contexts Process Virtual Memory Cross-Development Environment Embedded Linux Distributions Commercial Linux Distributions Do-It-Yourself Linux Distributions Summary Suggestions for Additional Reading 35 Chapter 3 Processor Basics Stand-Alone Processors IBM 970FX Intel Pentium M 39

4 Contents ix Intel Atom Freescale MPC Companion Chipsets 4l 3.2 Integrated Processors: Systems on Chip Power Architecture Freescale Power Architecture Freescale PowerQUICC I Freescale PowerQUICC II PowerQUICC II Pro Freescale PowerQUICC III Freescale QorlQ AMCC Power Architecture MIPS Broadcom MIPS Other MIPS ARM TIARM Freescale ARM Other ARM Processors Other Architectures Hardware Platforms CompactPCI ATCA Summary Suggestions for Additional Reading 62

5 x Embedded Linux Primer, Second Edition Chapter 4 The Linux Kernel: A Different Perspective Background Kernel Versions Kernel Source Repositories Using git to Download a Kernel Linux Kernel Construction Top-Level Source Directory Compiling the Kernel The Kernel Proper: vmlinux Kernel Image Components Subdirectory Layout Kernel Build System The Dot-Config Configuration Editor(s) Makefile Targets Kernel Configuration Custom Configuration Options Kernel Makefiles Kernel Documentation Obtaining a Custom Linux Kernel What Else Do I Need? Summary Suggestions for Additional Reading 98 Chapter 5 Kernel Initialization Composite Kernel Image: Piggy and Friends The Image Object Architecture Objects 104

6 Contents xi Bootstrap Loader Boot Messages Initialization Flow of Control Kernel Entry Point: head. o Ill Kernel Startup: main. c Architecture Setup Kernel Command-Line Processing The setup Macro Subsystem Initialization The * initcall Macros The init Thread Initialization Via initcalls initcall_debug Final Boot Steps Summary Suggestions for Additional Reading 130 Chapter 6 User Space Initialization Root File System FHS: File System Hierarchy Standard File System Layout Minimal File System The Embedded Root FS Challenge Trial-and-Error Method Automated File System Build Tools 137

7 xii Embedded Linux Primer, Second Edition 6.2 Kernel's Last Boot Steps First User Space Program Resolving Dependencies Customized Initial Process The init Process inittab Sample Web Server Startup Script Initial RAM Disk Booting with initrd Bootloader Support for initrd initrd Magic: linuxrc The initrd Plumbing Building an initrd Image Using initramfs Customizing initramfs Shutdown Summary Suggestions for Additional Reading 157 Chapter 7 Bootloaders Role of a Bootloader Bootloader Challenges DRAM Controller Flash Versus RAM Image Complexity Execution Context 165

8 Contents xiii 7.3 A Universal Bootloader: Das U-Boot Obtaining U-Boot Configuring U-Boot U-Boot Monitor Commands Network Operations Storage Subsystems Booting from Disk Porting U-Boot EP405 U-Boot Port U-Boot Makefile Configuration Target EP405 First Build EP405 Processor Initialization Board-Specific Initialization Porting Summary U-Boot Image Format Device Tree Blob (Flat Device Tree) Device Tree Source Device Tree Compiler Alternative Kernel Images Using DTB Other Bootloaders Lilo GRUB Still More Bootloaders Summary Suggestions for Additional Reading 198

9 xiv Embedded Linux Primer, Second Edition Chapter 8 Device Driver Basics Device Driver Concepts Loadable Modules Device Driver Architecture Minimal Device Driver Example Module Build Infrastructure Installing a Device Driver Loading a Module Module Parameters Module Utilities insmod Ismod modprobe depmod rmmod modinfo Driver Methods Driver File System Operations Allocation of Device Numbers Device Nodes and mknod B ringing It All Together Building Out-of-Tree Drivers Device Drivers and the GPL Summary Suggestions for Additional Reading 226

10 Contents xv Chapter 9 File Systems Linux File System Concepts Partitions ext2 : Mounting a File System Checking File System Integrity ext ext ReiserFS JFFS Building a JFFS2 Image cramfs Network File System Root File System on NFS Pseudo File Systems /proc File System sysfs Other File Systems Building Simple File a System Summary Suggestions for Additional Reading 259 Chapter 10 MTD Subsystem MTD Overview Enabling MTD Services MTD Basics Configuring MTD on Your Target 267

11 xvi Embedded Linux Primer, Second Edition 10.2 MTD Partitions Redboot Partition Table Partitioning Kernel Command-Line Partitioning Mapping Driver Flash Chip Drivers Board-Specific Initialization MTD Utilities JFFS2 Root File System UBI File System Configuring for UBIFS Building a UBIFS Image Using UBIFS as the Root File System Summary Suggestions for Additional Reading 288 Chapter 11 BusyBox Introduction to BusyBox BusyBox Is Easy BusyBox Configuration Cross-Compiling BusyBox BusyBox Operation BusyBox init Sample rcs Initialization Script BusyBox Target Installation BusyBox Applets Summary Suggestions for Additional Reading 304

12 Contents xvii Chapter 12 Embedded Development Environment Cross-Development Environment "Hello World" Embedded Host System Requirements Hardware Debug Probe Hosting Target Boards TFTP Server BOOTP/DHCP Server NFS Server Target NFS Root Mount U-Boot NFS Root Mount Example Summary Suggestions for Additional Reading 323 Chapter 13 Development Tools GNU Debugger (GDB) Debugging a Core Dump Invoking GDB Debug Session in GDB Data Display Debugger cbrowser/cscope Tracing and Profiling Tools strace strace Variations Itrace ' ps top 346

13 xviii [imbedded Linux Primer, Second Edition mfcrace dmalloc Kernel Oops Binary Utilities readelf Examining Debug Information Using readelf objdump objcopy Miscellaneous Binary Utilities strip addr21ine strings ldd nm prelink Summary Suggestions for Additional Reading 365 Chapter 14 Kernel Debugging Techniques Challenges to Kernel Debugging Using KGDB for Kernel Debugging KGDB Kernel Configuration Target Boot with KGDB Support Useful Kernel Breakpoints Sharing a Console Serial Port with KGDB Debugging Very Early Kernel Code KGDB Support in the Mainline Kernel 380

14 Contents xix 14.3 Kernel Debugging Techniques gdb Remote Serial Protocol Debugging Optimized Kernel Code GDB User-Defined Commands Useful Kernel GDB Macros Debugging Loadable Modules printk Debugging Magic SysReq Key Hardware-Assisted Debugging Programming Flash Using a JTAG Probe Debugging with a JTAG Probe When It Doesn't Boot Early Serial Debug Output Dumping the printk Log Buffer KGDB on Panic Summary Suggestions for Additional Reading 422 Chapter 15 Debugging Embedded Linux Applications Target Debugging Remote (Cross) Debugging gdbserver Debugging with Shared Libraries Shared Library Events in GDB Debugging Multiple Tasks Debugging Multiple Processes Debugging Multithreaded Applications Debugging Bootloader/Flash Code 441

15 xx Embedded Linux Primer, Second Edition 15.5 Additional Remote Debug Options Debugging Using a Serial Port Attaching to a Running Process Summary Suggestions for Additional Reading 444 Chapter 16 Open Source Build Systems Why Use a Build System? Scratchbox Installing Scratchbox Creating a Cross-Compilation Target Buildroot Buildroot Installation Buildroot Configuration Buildroot Build OpenEmbedded OpenEmbedded Composition BitBake Metadata Recipe Basics Metadata Tasks Metadata Classes Configuring OpenEmbedded Building Images Summary Suggestions for Additional Reading 464

16 Contents xxi Chapter 17 Linux and Real Time What Is Real Time? Soft Real Time Hard Real Time Linux Scheduling Latency Kernel Preemption Impediments to Preemption Preemption Models SMP Kernel Sources of Preemption Latency Real-Time Kernel Patch Real-Time Features O(l) Scheduler Creating a Real-Time Process Real-Time Kernel Performance Analysis Using Ftrace for Tracing Preemption Off Latency Measurement Walceup Latency Measurement Interrupt Off Timing Soft Lockup Detection Summary Suggestion for Additional Reading 485 Chapter 18 Universal Serial Bus USB Overview USB Physical Topology USB Logical Topology 490

17 xxii Embedded Linux Primer, Second Edition USB Revisions USB Connectors USB Cable Assemblies USB Modes Configuring USB USB Initialization sysfs and USB Device Naming Useful USB Tools USB File System Using usbview USBUtils(lsusb) Common USB Subsystems USB Mass Storage Class USB HID Class USB CDC Class Drivers USB Network Support USB Debug usbraon Useful USB Miscellanea Summary Suggestions for Additional Reading 519 Chapter 19 udev What Is udev? Device Discovery Default udev Behavior 525

18 Contents xxiii 19.4 Understanding udev Rules Modalias Typical udev Rules Configuration Initial System Setup for udev Loading Platform Device Drivers Customizing udev Behavior udev Customization Example: USB Automounting Persistent Device Naming udev Helper Utilities Using udev with busybox busybox Configuring mdev 545 mdev Summary Suggestions for Additional Reading 548 Appendix A GNU Public License 549 Preamble 550 Terms and Conditions for Copying, Distribution, and Modification 551 No Warranty 555 Appendix B U-Boot Configurable Commands 557 Appendix C BusyBox Commands 561 Appendix D SDRAM Interface Considerations 571 D.l SDRAM Basics 572 D.l.l SDRAM Refresh 573 D.2 Clocking 574

19 xxiv Embedded Linux Primer, Second Edition D.3 SDRAM Setup 575 D.4 Summary 580 D.4.1 Suggestions for Additional Reading 580 Appendix E Open Source Resources 581 Source Repositories and Developer Information 582 Mailing Lists 582 Linux News and Developments 583 Open Source Legal Insight and Discussion 583 Appendix F Sample BDI-2000 Configuration File 585 Index 593