IIO libiio

Applicable for

STM32MP13x lines, STM32MP15x lines, STM32MP25x lines

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Libiio is a complete library which offers tools and an interface to develop an application using IIO subsystem.

1. Article purpose

The purpose of this article is to:

• briefly introduce the libiio main features and API
• provide few examples, using libiio tools

2. Introduction

• Libiio is a user space library that provides an interface for user space applications. It is basically a wrapper that resides above the following interfaces:

1. /sys/bus/iio/devices sysfs interface (for configuration/setting)
2. /dev/iio/deviceX device interface (for data)

• Libiio also provides tools that can be used for testing
• Libiio design goals:

1. Interface with the kernel, to access IIO devices
2. Provide proper data structures and functions to the user application
3. Support for local and remote backends allowing applications to access the devices when running on a local or a remote machine

The full description of the IIO library is provided by the author of the library, see below references:

• What is libiio.
• About libiio.

3. API description

The API description can be found here: https://analogdevicesinc.github.io/libiio

4. Tools

Libiio offers tools such as:

• iiod server daemon
• iio_info to dump attributes

root@stm32mp1:~# iio_info 
Library version: 0.8 (git tag: v0.8)
IIO context created with local backend.
Backend version: 0.8 (git tag: v0.8)
Backend description string: Linux stm32mp1 4.14.0-00004-gafe4a31 #778 SMP PREEMPT Tue Aug 28 14:02:25 CEST 2018 armv7l
IIO context has 3 devices:
        trigger1: tim6_trgo
                0 channels found:
                3 device-specific attributes found:
                                attr 0: sampling_frequency value: 100
                                attr 1: master_mode value: reset
                                attr 2: master_mode_available value: reset enable update compare_pulse OC1REF OC2REF OC3REF OC4REF
        iio:device0: 48003000.adc:adc@0 (buffer capable)
                2 channels found:
                        voltage0:  (input, index: 0, format: le:U16/16>>0)
                        3 channel-specific attributes found:
                                attr 0: raw value: 72
                                attr 1: offset value: 0
                                attr 2: scale value: 0.044250488
                        voltage1:  (input, index: 1, format: le:U16/16>>0)
                        3 channel-specific attributes found:
                                attr 0: raw value: 1746
                                attr 1: offset value: 0
                                attr 2: scale value: 0.044250488
...

• iio_readdev (to read or scan from a device)

STM32AP [rc=0]# iio_readdev -t trigger1 -s 8 -b 8 iio:device0 voltage0 voltage1 | hexdump
0000000 0068 055a 0058 0520 00b4 03df 0070 055f
0000010 0096 03d6 0089 038f 0077 05c8 0096 03b3

See also: How to use the IIO user space interface

5. Source code

Libiio can be downloaded on a public github. It can be cloned using git command:

git clone https://github.com/analogdevicesinc/libiio.git

Tools source code can be found under libiio "tests" directory.

6. Installation on your target

Libiio and the tools it provides are embedded by default in OpenSTLinux distribution.

Application programming interface

System file system (see https://en.wikipedia.org/wiki/Sysfs for more details)

Industrial I/O Linux^® subsystem

Linux^® is a registered trademark of Linus Torvalds.

Symetric multiprocessing

Application programming interface

System file system (see https://en.wikipedia.org/wiki/Sysfs for more details)

Industrial I/O Linux^® subsystem

Linux^® is a registered trademark of Linus Torvalds.

Symetric multiprocessing