How to read iio device in user space

[deepanrajanbara]

Hi,

we are using a custom sensor which uses iio subsystem.We are able to read the data from the device in filesystem using cat and echo commands. But how do i read the data from the device in my application.Is there any sample code available to test my iio device.

Thank you,

Deepanraj.A

[Carlos_Musich]

Hi Depanraj,

you may find useful this documents Interfacing FXLS8471Q with i.MX6Q 

Regards,
Carlos
NXP Technical Support
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[deepanrajanbara]

Hi Carlos,

In this example it is connected to spi. But in my case we wanted to read the device data by opening the node /dev/iio:device0.

[Carlos_Musich]

Hi Deepanraj,

The iio subsystem provides two ways to program the ADC and read the values:

1. One-shot conversions performed by reading the files in /sys/bus/iio/devices/iio\:device0/
2. Continuous conversions of a single channel at a time using the /dev/iio:device0 character device file

There is no other API. Nothing like an ioctl that would let you program the device and do multiple conversions and read the results with a single system call. So you need to write your own code to open the /sys/bus/iio/devices/iio\:device0/ files, read the contents, and convert them from ASCII to unsigned int for doing whatever your program needs to do with the values.

The iioutils package (http://sourceforge.net/projects/iioutils/) does all of this for you, so that's probably the best place to copy the code from.

There is some nice backgroud documentation for other processors and sensors on http://processors.wiki.ti.com/index.php/AM335x_ADC_Driver%27s_Guide and in Enabling input (sensor) access for ARM devices : Blueprints : Ubuntu.

There is also a libiio package (analogdevicesinc/libiio · GitHub) that adds a lot of syntactic sugar, but at the lower level doesn't do things differently than iioutils.

Regards,
Carlos
NXP Technical Support
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