One of the large segments in the IT industry today is the development of device drivers — specially designed pieces of software that enable the communication of hardware with high-level software. With the help of drivers, you can control physical devices and make them operate as intended. This is especially crucial for embedded solutions and the rapidly growing Internet of Things market.

Linux device drivers development is one of the most demanded service of IT companies, because Linux is the basis for the majority of modern IoT and embedded projects. In this article, we offer a brief overview of the Linux OS and the process of developing drivers for it.

What is Linux?

Linux is an operating system (or more precisely, a family of systems) originated from Unix and based on the Linux kernel, which was created by Linus Torvalds in 1991. For over two decades, Linux has been the main system for mobile devices, servers, embedded solutions, and even personal computers.

Thanks to the free and open-source model, thousands of specialists worldwide contribute to Linux, making significant improvements and adding new features to the technology.

Moreover, Linux is platform-agnostic, which means that most of its source code doesn’t depend on the hardware platform it operates on. The OS needs drivers to be able to work on a particular hardware because drivers keep in them data on the device features.

Linux system architecture

Any system based on Linux comprises a set of typical elements:

Hardware — physical appliances (e.g., printers, terminals, HDD).
Kernel — the heart of the operating system that directly communicates with the hardware layer and transmits data from it to the upper elements.
Shell — an interface enabling interaction between users and the kernel. It transmits users’ commands to the central part of OS and runs operations, thus concealing the complexity of kernels’ functioning.
Applications — Linux distributions provide app stores where users can find applications that will meet their requirements and install them to the system.
Bootloader — a software program responsible for placing an OS into the hardware memory. The widely used bootloaders for Linux are LILO and LOADLIN.

Linux OS features and benefits

Free and open-source — multiple teams and individual developers from all over the world can freely use the Linux source code and alter it, making improvements and adding new capabilities, that’s why this technology is constantly evolving.
Portable — you can install Linux software on any hardware platform, and it will run flawlessly. This feature ensures the flexibility of Linux-based projects and gives more freedom to software developers.
Lightweight — compared to other operating systems, Linux is lightweight. It uses less memory and storage space, which is essential for embedded and Internet of Things solutions.
Multilingual — Linux can be used in various languages, hence its geography of usage is extensive.

Secure — Linux OS provides end-to-end encryption and authentication to keep critical data safe.

What are device drivers?

Device drivers play a special role in the Linux kernel. These are pieces of low-level software that process certain requests to the hardware through a well-organized internal interface. Typically, a device driver is a shared library that handles the peculiar features of hardware devices. However, you can create a driver for one particular device.

The operational features of each specific device are hidden in the driver code. User requests are sent through a standard set of system calls, which doesn’t depend on a particular driver but somewhat depends on the class of the device. These requests are mapped to hardware-specific functions that control real devices. And device drivers play the role of this set of functions.

Developing Linux device drivers: what you need to know

If you are a business owner, and you need device drivers for your project, you’d better turn to an embedded IT solutions company that provides relevant development services. Their specialists are experienced in developing, updating, packaging and porting drivers and can easily solve your issue.

For those who start their career as embedded developers, we provide some tips on what you need to know to write a driver for Linux.

First, you should clearly understand the functioning principles of Linux itself. Actually, the stages of driver development are similar for all operating systems, be it Windows, Linux or some other OS. If you once wrote a driver for Windows, creating a Linux driver will not be difficult, but you need to get a general vision of the system.
Then, you should be good in the C and Assembly languages, because the OS kernel is written in them.
Of course, you should learn the specifics of the hardware for which you are going to write software: the type of the device (SoC, SoM, etc.), its bus interface type, what communication protocol is uses, how to detect and initialize the device in the system, etc.

And finally, you need patience and desire to read the documentation and the source code.

The programming interface provides two options for creating drivers:

Implement drivers as part of the kernel, i.e., create an integrated system.

Write separate modules (specific files) and connect them to the kernel when needed. This option is more efficient because you don’t have to recompile the kernel, thus you can avoid issues and manage files easier.

To start writing your first driver for Linux, follow the guidance from the development documentation.

For example, if you write a module driver, the first functions you’ll need to create are load and unload. The my_init function will initialize your driver when starting the system, and the my_exit function will unload it when shutting down the system.

As soon as your simple driver is ready, it can interact with special files in the device tree. Device files are divided into two types:

Character files — represent data character by character
Block files — represent data in blocks

The final but no less important stage of driver creation is testing. You can use a virtual machine or a physical device to fine-tune and debug your driver. There are also tools such as SymDrive that eliminate the need to use hardware for testing.

Conclusion

An overwhelming majority of embedded solutions are based on Linux OS distributions nowadays. Device drivers play a critical role in the functioning of this operating system. That’s why the demand for driver development services remains high.

In this article, we outlined the basic information on Linux and what you should know to write custom device drivers from scratch.