Comprehensive Real-World Guidance for Every Embedded Developer and Engineer
This book brings together indispensable knowledge for building efficient, high-value, Linux-based embedded products: information that has never been assembled in one place before. Drawing on years of experience as an embedded Linux consultant and field application engineer, Christopher Hallinan offers solutions for the specific technical issues you're most likely to face, demonstrates how to build an effective embedded Linux environment, and shows how to use it as productively as possible.
Hallinan begins by touring a typical Linux-based embedded system, introducing key concepts and components, and calling attention to differences between Linux and traditional embedded environments. Writing from the embedded developer's viewpoint, he thoroughly addresses issues ranging from kernel building and initialization to bootloaders, device drivers to file systems.
Hallinan thoroughly covers the increasingly popular BusyBox utilities; presents a step-by-step walkthrough of porting Linux to custom boards; and introduces real-time configuration via CONFIG_RT--one of today's most exciting developments in embedded Linux. You'll find especially detailed coverage of using development tools to analyze and debug embedded systems--including the art of kernel debugging.
• Compare leading embedded Linux processors
• Understand the details of the Linux kernel initialization process
• Learn about the special role of bootloaders in embedded Linux systems, with specific emphasis on U-Boot
• Use embedded Linux file systems, including JFFS2--with detailed guidelines for building Flash-resident file system images
• Understand the Memory Technology Devices subsystem for flash (and other) memory devices
• Master gdb, KGDB, and hardware JTAG debugging
• Learn many tips and techniques for debugging within the Linux kernel
• Maximize your productivity in cross-development environments
• Prepare your entire development environment, including TFTP, DHCP, and NFS target servers
• Configure, build, and initialize BusyBox to support your unique requirements
6.4.6. Building an initrd Image
6.4.6. Building an initrd Image
Constructing a suitable root file system image is one of the more challenging aspects of embedded systems. Creating a proper initrd image is even more challenging because it needs to be small and specialized. For this section, we examine initrd requirements and file system contents.
Listing 6-12 was produced by running the tree utility on our example initrd image from this chapter.
Listing 6-12. Contents of Example initrd
.
|-- bin
| |-- busybox
| |-- echo -> busybox
| |-- mount -> busybox
| '-- sh -> busybox
|-- dev
| |-- console
| |-- ram0
| '-- ttyS0
|-- etc
|-- linuxrc
'-- proc
4 directories, 8 files
As you can see, it is very small indeed; it takes up a little more than 500KB in uncompressed form. Since it is based on busybox, it has many capabilities. Because busybox is statically linked, it has no dependencies on any system libraries. You will learn more about busybox in Chapter 11.
