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
15.4.3. Debugging Bootloader/Flash Code
15.4.3. Debugging Bootloader/Flash Code
Debugging Flash resident code presents its own unique challenges. The most obvious limitation is the way in which GDB and gdbserver cooperate in setting target breakpoints. When we discussed the GDB remote serial protocol in Chapter 14, you learned how breakpoints are inserted into an application.[104] GDB replaces the opcode at the breakpoint location with an architecture-specific opcode that passes control to the debugger. However, in ROM or Flash, GDB cannot overwrite the opcode, so this method of setting breakpoints is useless.
Most modern processors contain some number of debug registers that can be used to get around this limitation. These capabilities must be supported by architecture-and processor-specific hardware probes or stubs. The most common technique for debugging Flash and ROM resident code is to use JTAG hardware probes. These probes support the setting of processor-specific hardware breakpoints. This topic was covered in detail in Chapter 14. Refer back to Section 14.4.2, "Debugging with a JTAG Probe," for details.
