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
17.3.1.2. ISRs as Kernel Tasks
17.3.1.2. ISRs as Kernel Tasks
With CONFIG_PREEMPT_HARDIRQ selected, interrupt service routines[118] (ISRs) are forced to run in process context. This gives the developer control over the priority of ISRs because they become schedulable entities. As such, they also become preemptable to allow higher-priority hardware interrupts to be handled first.
This is a powerful feature. Some hardware architectures do not enforce interrupt priorities. Those that do might not enforce the priorities consistent with your specified real-time design goals. Using CONFIG_PREEMPT_HARDIRQ, you are free to define the priorities at which each IRQ will run.
Conversion of ISRs to threads can be disabled at runtime through the /proc file system or at boot time by entering a parameter on the kernel command line. When enabled in the configuration, unless you specify otherwise, ISR threading is enabled by default.
To disable ISR threading at runtime, issue the following command as root:
# echo '0' >/proc/sys/kernel/hardirq_preemption
To verify the setting, display it as follows:
# cat /proc/sys/kernel/hardirq_preemption
1
To disable ISR threading at boot time, add the following parameter to the kernel command line:
hardirq-preempt=0
