In this chapter, you are introduced to Linux kernel programming on an embedded device such as the Raspberry Pi (RPi). Kernel programming is an advanced topic that requires in-depth study of the source code for the Linux kernel; however, this chapter is structured as a practical step-by-step guide to the focused task of writing Linux loadable kernel modules (LKMs) that interface to general-purpose inputs/outputs (GPIOs). The first example is a straightforward “Hello World” module that can be used to establish a configuration for LKM development on the RPi. The second LKM example introduces interrupt service routines (ISRs), and interfaces a simple GPIO button and LED circuit to Linux kernel space. Two further examples are provided that introduce the kobject interface and the use of kernel threads to build kernel-space sysfs devices for the RPi. By the end of this chapter, you should be familiar with the steps required to write kernel code, and appreciate the programming constraints that such development entails.
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As introduced in Chapter 3, a loadable kernel module (LKM) is a mechanism for adding code to, or removing code from, the Linux kernel at run time. They are ideal for device drivers, enabling the kernel to communicate with the hardware without it having to know how the hardware works. ...