Book Image

Mastering Linux Device Driver Development

By : John Madieu
Book Image

Mastering Linux Device Driver Development

By: John Madieu

Overview of this book

Linux is one of the fastest-growing operating systems around the world, and in the last few years, the Linux kernel has evolved significantly to support a wide variety of embedded devices with its improved subsystems and a range of new features. With this book, you’ll find out how you can enhance your skills to write custom device drivers for your Linux operating system. Mastering Linux Device Driver Development provides complete coverage of kernel topics, including video and audio frameworks, that usually go unaddressed. You’ll work with some of the most complex and impactful Linux kernel frameworks, such as PCI, ALSA for SoC, and Video4Linux2, and discover expert tips and best practices along the way. In addition to this, you’ll understand how to make the most of frameworks such as NVMEM and Watchdog. Once you’ve got to grips with Linux kernel helpers, you’ll advance to working with special device types such as Multi-Function Devices (MFD) followed by video and audio device drivers. By the end of this book, you’ll be able to write feature-rich device drivers and integrate them with some of the most complex Linux kernel frameworks, including V4L2 and ALSA for SoC.
Table of Contents (19 chapters)
1
Section 1:Kernel Core Frameworks for Embedded Device Driver Development
6
Section 2: Multimedia and Power Saving in Embedded Linux Systems
13
Section 3: Staying Up to Date with Other Linux Kernel Subsystems

Chapter 13: Watchdog Device Drivers

A watchdog is a hardware (sometimes emulated by software) device intended to ensure the availability of a given system. It helps make sure that the system always reboots upon a critical hang, thus allowing to monitor the "normal" behavior of the system.

Whether it is hardware-based or emulated by software, the watchdog is, most of the time, nothing but a timer initialized with a reasonable timeout that should be periodically refreshed by software running on the monitored system. If for any reason the software stops/fails at refreshing the timer (and has not explicitly shut it down) before it expires (it runs to timeout), this will trigger a (hardware) reset of the whole system (the computer, in our case). Such a mechanism can even help with recovering from a kernel panic. By the end of this chapter, you will be able to do the following:

  • Read/understand an existing watchdog kernel driver and use what it exposes in user space.
  • ...