BeagleBone Blog
Writing a Linux Kernel Module — Part 3: Buttons and LEDs
Introduction
In this series of articles I describe how you can write a Linux loadable kernel module (LKM) for an embedded Linux device. This is the third article in the series — please read:
Writing a Linux Kernel Module — Part 1: Introduction, and
Writing a Linux Kernel Module — Part 2: A Character Device,
before moving on to this article, as those articles explain how to build, load and unload loadable kernel modules (LKMs) and character device drivers. Such detail is not repeated in this article.
This article describes how you can write kernel code that interfaces to custom electronics circuits that are attached to the GPIOs of a Linux embedded system, and how you can add enhanced functionality for such devices that is not available by default under embedded Linux. The BeagleBone is used as the deployment platform for this article, and while it is desirable that you use the BeagleBone in order […]
Writing a Linux Kernel Module — Part 2: A Character Device
Introduction
In this series of articles I describe how you can write a Linux loadable kernel module (LKM) for an embedded Linux device. This is the second article in the series — please read “Writing a Linux Kernel Module — Part 1: Introduction” before moving on to this article, as it explains how to build, load and unload loadable kernel modules (LKMs). Such description is not repeated in this article.
Character Device Drivers
A character device typically transfers data to and from a user application — they behave like pipes or serial ports, instantly reading or writing the byte data in a character-by-character stream. They provide the framework for many typical drivers, such as those that are required for interfacing to serial communications, video capture, and audio devices. The main alternative to a character device is a block device. Block devices behave in a similar fashion to regular files, allowing a buffered […]
Writing a Linux Kernel Module — Part 1: Introduction
Introduction
In this series of articles I describe how you can write a Linux kernel module for an embedded Linux device. I begin with a straightforward “Hello World!” loadable kernel module (LKM) and work towards developing a module that can control GPIOs on an embedded Linux device (such as the BeagleBone) through the use of IRQs. I will add further follow-up articles as I identify suitable applications.
This is a complex topic that will take time to work through. Therefore, I have broken the discussion up over a number of articles, each providing a practical example and outcome. There are entire books written on this topic, so it will be difficult to cover absolutely every aspect. There are also other articles available on writing kernel modules; however, the examples presented here are built and tested under the Linux kernel 3.8.X+, ensuring that the material is up to date and relevant, and I […]
Introduction to CMake by Example
Introduction
This article provides a straightforward set of “Hello World!” introductions to using CMake for building C++ projects. All steps are performed using Linux on the BeagleBone platform, but the instructions are relevant to most Linux platforms.
The make utility and Makefiles provide a build system that can be used to manage the compilation and re-compilation of programs that are written in any programming language. I use Makefiles quite often in my projects to automate the build process; however, there are times when Makefiles become overly complex for the task — particularly when building projects that have multiple sub directories, or projects that are to be deployed to multiple platforms.
Building complex projects is where CMake really shines — CMake is a cross-platform Makefile generator! Simply put, CMake automatically generates the Makefiles for your project. It can do much more than that too (e.g., build MS Visual Studio solutions), but in this discussion I focus on […]
CGI using C++ on the BeagleBone (Ggicc)
Introduction
In Chapter 10 of my book (pg. 388-393), Exploring BeagleBone, I describe how you can build web-based CGI applications that can interface with electronics hardware that is attached to the BeagleBone using Bash scripts that call C/C++ programs. The solution works well for very straightforward applications, but this discussion investigates more advanced solutions for applications where there are more complex interactions — for example, the use of web forms to pass data between your web browser and the application that is executing on the BeagleBone. In this discussion I begin by explaining how you can use a C/C++ program, rather than a CGI script, to display a web page. I then investigate the use of the GNU Cgicc library for more structured and complex interactions.
The approach describe here will work on any Linux machine, including other embedded platforms such as the Raspberry PI; however, the steps are structured for the BeagleBone platform and the […]