Book Image

Linux Device Driver Development - Second Edition

By : John Madieu
Book Image

Linux Device Driver Development - Second Edition

By: John Madieu

Overview of this book

Linux is by far the most-used kernel on embedded systems. Thanks to its subsystems, the Linux kernel supports almost all of the application fields in the industrial world. This updated second edition of Linux Device Driver Development is a comprehensive introduction to the Linux kernel world and the different subsystems that it is made of, and will be useful for embedded developers from any discipline. You'll learn how to configure, tailor, and build the Linux kernel. Filled with real-world examples, the book covers each of the most-used subsystems in the embedded domains such as GPIO, direct memory access, interrupt management, and I2C/SPI device drivers. This book will show you how Linux abstracts each device from a hardware point of view and how a device is bound to its driver(s). You’ll also see how interrupts are propagated in the system as the book covers the interrupt processing mechanisms in-depth and describes every kernel structure and API involved. This new edition also addresses how not to write device drivers using user space libraries for GPIO clients, I2C, and SPI drivers. By the end of this Linux book, you’ll be able to write device drivers for most of the embedded devices out there.
Table of Contents (23 chapters)
1
Section 1 -Linux Kernel Development Basics
6
Section 2 - Linux Kernel Platform Abstraction and Device Drivers
12
Section 3 - Making the Most out of Your Hardware
18
Section 4 - Misc Kernel Subsystems for the Embedded World

Accessing IIO data

You may have guessed, there are only two ways to access data with the IIO framework: one-shot capture through sysfs channels or continuous mode (triggered buffer) via an IIO character device.

Single-shot capture

Single-shot data capture is done through the sysfs interface. By reading the sysfs entry that corresponds to a channel, you'll capture only the data specific to that channel. Say we have a temperature sensor with two channels: one for the ambient temperature and the other for the thermocouple temperature:

# cd /sys/bus/iio/devices/iio:device0
# cat in_voltage3_raw
6646 
# cat in_voltage_scale
0.305175781

The processed value is obtained by multiplying the scale by the raw value:

Voltage value: 6646 * 0.305175781 = 2028.19824053

The device datasheet says the process value is given in mV. In our case, it corresponds to 2.02819 V.

Accessing the data buffer

To get a triggered acquisition working, trigger support must have been implemented...