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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Chapter 2. Industrial I/O core</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="Industrial I/O driver developer's guide"><link rel="up" href="index.html" title="Industrial I/O driver developer's guide"><link rel="prev" href="intro.html" title="Chapter 1. Introduction"><link rel="next" href="API-struct-iio-dev.html" title="struct iio_dev"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 2. Industrial I/O core</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="intro.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="API-struct-iio-dev.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="iiosubsys"></a>Chapter 2. Industrial I/O core</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="sect1"><a href="iiosubsys.html#iiodevice"> Industrial I/O devices </a></span></dt><dd><dl><dt><span class="sect2"><a href="iiosubsys.html#iioattr"> IIO device sysfs interface </a></span></dt><dt><span class="sect2"><a href="iiosubsys.html#iiochannel"> IIO device channels </a></span></dt></dl></dd><dt><span class="sect1"><a href="iiobuffer.html"> Industrial I/O buffers </a></span></dt><dd><dl><dt><span class="sect2"><a href="iiobuffer.html#iiobuffersysfs">IIO buffer sysfs interface </a></span></dt><dt><span class="sect2"><a href="iiobuffer.html#iiobuffersetup"> IIO buffer setup </a></span></dt></dl></dd><dt><span class="sect1"><a href="iiotrigger.html"> Industrial I/O triggers  </a></span></dt><dd><dl><dt><span class="sect2"><a href="iiotrigger.html#iiotrigsysfs"> IIO trigger sysfs interface </a></span></dt><dt><span class="sect2"><a href="iiotrigger.html#iiotrigattr"> IIO trigger setup</a></span></dt><dt><span class="sect2"><a href="iiotrigger.html#iiotrigsetup"> IIO trigger ops</a></span></dt></dl></dd><dt><span class="sect1"><a href="iiotriggered_buffer.html"> Industrial I/O triggered buffers </a></span></dt><dd><dl><dt><span class="sect2"><a href="iiotriggered_buffer.html#iiotrigbufsetup"> IIO triggered buffer setup</a></span></dt></dl></dd></dl></div><p>
      The Industrial I/O core offers:
      </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
         a unified framework for writing drivers for many different types of
         embedded sensors.
        </li><li class="listitem">
         a standard interface to user space applications manipulating sensors.
        </li></ul></div><p>
      The implementation can be found under <code class="filename">
      drivers/iio/industrialio-*</code>
  </p><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="iiodevice"></a> Industrial I/O devices </h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="refentrytitle"><a href="API-struct-iio-dev.html"><span class="phrase">struct iio_dev</span></a></span><span class="refpurpose"> —
  industrial I/O device
 </span></dt><dt><span class="refentrytitle"><a href="API-iio-device-alloc.html"><span class="phrase">iio_device_alloc</span></a></span><span class="refpurpose"> —
  allocate an iio_dev from a driver
 </span></dt><dt><span class="refentrytitle"><a href="API-iio-device-free.html"><span class="phrase">iio_device_free</span></a></span><span class="refpurpose"> —
  free an iio_dev from a driver
 </span></dt><dt><span class="refentrytitle"><a href="API-iio-device-register.html"><span class="phrase">iio_device_register</span></a></span><span class="refpurpose"> —
  register a device with the IIO subsystem
 </span></dt><dt><span class="refentrytitle"><a href="API-iio-device-unregister.html"><span class="phrase">iio_device_unregister</span></a></span><span class="refpurpose"> —
  unregister a device from the IIO subsystem
 </span></dt><dt><span class="sect2"><a href="iiosubsys.html#iioattr"> IIO device sysfs interface </a></span></dt><dt><span class="sect2"><a href="iiosubsys.html#iiochannel"> IIO device channels </a></span></dt></dl></div><p>
      An IIO device usually corresponds to a single hardware sensor and it
      provides all the information needed by a driver handling a device.
      Let's first have a look at the functionality embedded in an IIO
      device then we will show how a device driver makes use of an IIO
      device.
    </p><p>
        There are two ways for a user space application to interact
        with an IIO driver.
      </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="filename">/sys/bus/iio/iio:deviceX/</code>, this
          represents a hardware sensor and groups together the data
          channels of the same chip.
        </li><li class="listitem"><code class="filename">/dev/iio:deviceX</code>, character device node
          interface used for buffered data transfer and for events information
          retrieval.
        </li></ul></div><p>
    </p>
    A typical IIO driver will register itself as an I2C or SPI driver and will
    create two routines, <code class="function"> probe </code> and <code class="function"> remove
    </code>. At <code class="function">probe</code>:
    <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">call <code class="function">iio_device_alloc</code>, which allocates memory
      for an IIO device.
    </li><li class="listitem"> initialize IIO device fields with driver specific information
              (e.g. device name, device channels).
    </li><li class="listitem">call <code class="function"> iio_device_register</code>, this registers the
      device with the IIO core. After this call the device is ready to accept
      requests from user space applications.
    </li></ul></div>
      At <code class="function">remove</code>, we free the resources allocated in
      <code class="function">probe</code> in reverse order:
    <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="function">iio_device_unregister</code>, unregister the device
      from the IIO core.
    </li><li class="listitem"><code class="function">iio_device_free</code>, free the memory allocated
      for the IIO device.
    </li></ul></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="iioattr"></a> IIO device sysfs interface </h3></div></div></div><p>
        Attributes are sysfs files used to expose chip info and also allowing
        applications to set various configuration parameters. For device
        with index X, attributes can be found under
        <code class="filename">/sys/bus/iio/iio:deviceX/ </code> directory.
        Common attributes are:
        </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="filename">name</code>, description of the physical
            chip.
          </li><li class="listitem"><code class="filename">dev</code>, shows the major:minor pair
            associated with <code class="filename">/dev/iio:deviceX</code> node.
          </li><li class="listitem"><code class="filename">sampling_frequency_available</code>,
            available discrete set of sampling frequency values for
            device.
          </li></ul></div><p>
      Available standard attributes for IIO devices are described in the
      <code class="filename">Documentation/ABI/testing/sysfs-bus-iio </code> file
      in the Linux kernel sources.
      </p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="iiochannel"></a> IIO device channels </h3></div></div></div><div class="toc"><dl class="toc"><dt><span class="refentrytitle"><a href="API-struct-iio-chan-spec.html"><span class="phrase">struct iio_chan_spec</span></a></span><span class="refpurpose"> —
  specification of a single channel
 </span></dt></dl></div><p>
        An IIO device channel is a representation of a data channel. An
        IIO device can have one or multiple channels. For example:
        </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
          a thermometer sensor has one channel representing the
          temperature measurement.
          </li><li class="listitem">
          a light sensor with two channels indicating the measurements in
          the visible and infrared spectrum.
          </li><li class="listitem">
          an accelerometer can have up to 3 channels representing
          acceleration on X, Y and Z axes.
          </li></ul></div><p>
      An IIO channel is described by the <span class="type"> struct iio_chan_spec
      </span>. A thermometer driver for the temperature sensor in the
      example above would have to describe its channel as follows:
      </p><pre class="programlisting">
      static const struct iio_chan_spec temp_channel[] = {
          {
              .type = IIO_TEMP,
              .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
          },
      };

      </pre><p>
      Channel sysfs attributes exposed to userspace are specified in
      the form of <span class="emphasis"><em>bitmasks</em></span>. Depending on their
      shared info, attributes can be set in one of the following masks:
      </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="emphasis"><em>info_mask_separate</em></span>, attributes will
        be specific to this channel</li><li class="listitem"><span class="emphasis"><em>info_mask_shared_by_type</em></span>,
        attributes are shared by all channels of the same type</li><li class="listitem"><span class="emphasis"><em>info_mask_shared_by_dir</em></span>, attributes
        are shared by all channels of the same direction </li><li class="listitem"><span class="emphasis"><em>info_mask_shared_by_all</em></span>,
        attributes are shared by all channels</li></ul></div><p>
      When there are multiple data channels per channel type we have two
      ways to distinguish between them:
      </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> set <span class="emphasis"><em> .modified</em></span> field of <span class="type">
        iio_chan_spec</span> to 1. Modifiers are specified using
        <span class="emphasis"><em>.channel2</em></span> field of the same
        <span class="type">iio_chan_spec</span> structure and are used to indicate a
        physically unique characteristic of the channel such as its direction
        or spectral response. For example, a light sensor can have two channels,
        one for infrared light and one for both infrared and visible light.
      </li><li class="listitem"> set <span class="emphasis"><em>.indexed </em></span> field of
        <span class="type">iio_chan_spec</span> to 1. In this case the channel is
        simply another instance with an index specified by the
        <span class="emphasis"><em>.channel</em></span> field.
      </li></ul></div><p>
      Here is how we can make use of the channel's modifiers:
      </p><pre class="programlisting">
      static const struct iio_chan_spec light_channels[] = {
          {
              .type = IIO_INTENSITY,
              .modified = 1,
              .channel2 = IIO_MOD_LIGHT_IR,
              .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
              .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ),
          },
          {
              .type = IIO_INTENSITY,
              .modified = 1,
              .channel2 = IIO_MOD_LIGHT_BOTH,
              .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
              .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ),
          },
          {
              .type = IIO_LIGHT,
              .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
              .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ),
          },

      }
      </pre><p>
      This channel's definition will generate two separate sysfs files
      for raw data retrieval:
      </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="filename">/sys/bus/iio/iio:deviceX/in_intensity_ir_raw</code></li><li class="listitem"><code class="filename">/sys/bus/iio/iio:deviceX/in_intensity_both_raw</code></li></ul></div><p>
      one file for processed data:
      </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="filename">/sys/bus/iio/iio:deviceX/in_illuminance_input
      </code></li></ul></div><p>
      and one shared sysfs file for sampling frequency:
      </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="filename">/sys/bus/iio/iio:deviceX/sampling_frequency.
      </code></li></ul></div><p>
      </p><p>
      Here is how we can make use of the channel's indexing:
      </p><pre class="programlisting">
      static const struct iio_chan_spec light_channels[] = {
          {
              .type = IIO_VOLTAGE,
              .indexed = 1,
              .channel = 0,
              .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
          },
          {
              .type = IIO_VOLTAGE,
              .indexed = 1,
              .channel = 1,
              .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
          },
      }
      </pre><p>
      This will generate two separate attributes files for raw data
      retrieval:
      </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="filename">/sys/bus/iio/devices/iio:deviceX/in_voltage0_raw</code>,
          representing voltage measurement for channel 0.
      </li><li class="listitem"><code class="filename">/sys/bus/iio/devices/iio:deviceX/in_voltage1_raw</code>,
          representing voltage measurement for channel 1.
      </li></ul></div><p>
      </p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="intro.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="API-struct-iio-dev.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 1. Introduction </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> <span class="phrase">struct iio_dev</span></td></tr></table></div></body></html>