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Linux Device Driver Development

You're reading from   Linux Device Driver Development Everything you need to start with device driver development for Linux kernel and embedded Linux

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Product type Paperback
Published in Apr 2022
Publisher Packt
ISBN-13 9781803240060
Length 708 pages
Edition 2nd Edition
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Author (1):
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John Madieu John Madieu
Author Profile Icon John Madieu
John Madieu
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Toc

Table of Contents (23) Chapters Close

Preface 1. Section 1 -Linux Kernel Development Basics
2. Chapter 1: Introduction to Kernel Development FREE CHAPTER 3. Chapter 2: Understanding Linux Kernel Module Basic Concepts 4. Chapter 3: Dealing with Kernel Core Helpers 5. Chapter 4: Writing Character Device Drivers 6. Section 2 - Linux Kernel Platform Abstraction and Device Drivers
7. Chapter 5: Understanding and Leveraging the Device Tree 8. Chapter 6: Introduction to Devices, Drivers, and Platform Abstraction 9. Chapter 7: Understanding the Concept of Platform Devices and Drivers 10. Chapter 8: Writing I2C Device Drivers 11. Chapter 9: Writing SPI Device Drivers 12. Section 3 - Making the Most out of Your Hardware
13. Chapter 10: Understanding the Linux Kernel Memory Allocation 14. Chapter 11: Implementing Direct Memory Access (DMA) Support 15. Chapter 12: Abstracting Memory Access – Introduction to the Regmap API: a Register Map Abstraction 16. Chapter 13: Demystifying the Kernel IRQ Framework 17. Chapter 14: Introduction to the Linux Device Model 18. Section 4 - Misc Kernel Subsystems for the Embedded World
19. Chapter 15: Digging into the IIO Framework 20. Chapter 16: Getting the Most Out of the Pin Controller and GPIO Subsystems 21. Chapter 17: Leveraging the Linux Kernel Input Subsystem 22. Other Books You May Enjoy

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...

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