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Message-Id: <1438094234-2894-2-git-send-email-daniel.baluta@intel.com>
Date: Tue, 28 Jul 2015 17:37:14 +0300
From: Daniel Baluta <daniel.baluta@...el.com>
To: jic23@...nel.org, corbet@....net, rdunlap@...radead.org
Cc: pmeerw@...erw.net, knaack.h@....de, lars@...afoo.de,
linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
herbert@...dor.apana.org.au, smueller@...onox.de, mmarek@...e.cz,
daniel.baluta@...el.com, linux-doc@...r.kernel.org,
cristina.opriceana@...il.com
Subject: [PATCH v3] DocBook: Add initial documentation for IIO
This is intended to help developers faster find their way
inside the Industrial I/O core and reduce time spent on IIO
drivers development.
Signed-off-by: Daniel Baluta <daniel.baluta@...el.com>
---
Documentation/DocBook/Makefile | 2 +-
Documentation/DocBook/iio.tmpl | 701 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 702 insertions(+), 1 deletion(-)
create mode 100644 Documentation/DocBook/iio.tmpl
diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile
index b6a6a2e..9e08606 100644
--- a/Documentation/DocBook/Makefile
+++ b/Documentation/DocBook/Makefile
@@ -15,7 +15,7 @@ DOCBOOKS := z8530book.xml device-drivers.xml \
80211.xml debugobjects.xml sh.xml regulator.xml \
alsa-driver-api.xml writing-an-alsa-driver.xml \
tracepoint.xml drm.xml media_api.xml w1.xml \
- writing_musb_glue_layer.xml crypto-API.xml
+ writing_musb_glue_layer.xml crypto-API.xml iio.xml
include Documentation/DocBook/media/Makefile
diff --git a/Documentation/DocBook/iio.tmpl b/Documentation/DocBook/iio.tmpl
new file mode 100644
index 0000000..0d696e2
--- /dev/null
+++ b/Documentation/DocBook/iio.tmpl
@@ -0,0 +1,701 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+ "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="iioid">
+ <bookinfo>
+ <title>Industrial I/O driver developer's guide </title>
+
+ <authorgroup>
+ <author>
+ <firstname>Daniel</firstname>
+ <surname>Baluta</surname>
+ <affiliation>
+ <address>
+ <email>daniel.baluta@...el.com</email>
+ </address>
+ </affiliation>
+ </author>
+ </authorgroup>
+
+ <copyright>
+ <year>2015</year>
+ <holder>Intel Corporation</holder>
+ </copyright>
+
+ <legalnotice>
+ <para>
+ This documentation is free software; you can redistribute
+ it and/or modify it under the terms of the GNU General Public
+ License version 2.
+ </para>
+ </legalnotice>
+ </bookinfo>
+
+ <toc></toc>
+
+ <chapter id="intro">
+ <title>Introduction</title>
+ <para>
+ The main purpose of the Industrial I/O subsystem (IIO) is to provide
+ support for devices that in some sense perform either analog-to-digital
+ conversion (ADC) or digital-to-analog conversion (DAC) or both. The aim
+ is to fill the gap between the somewhat similar hwmon and input
+ subsystems.
+ Hwmon is very much directed at low sample rate sensors used in
+ applications such as fan speed control and temperature measurement. Input
+ is, as its name suggests, focused on human interaction input devices
+ (keyboard, mouse, touchscreen). In some cases there is considerable
+ overlap between these and IIO.
+ </para>
+ <para>
+ Devices that fall into this category include:
+ <itemizedlist>
+ <listitem>
+ analog to digital converters (ADCs)
+ </listitem>
+ <listitem>
+ accelerometers
+ </listitem>
+ <listitem>
+ capacitance to digital converters (CDCs)
+ </listitem>
+ <listitem>
+ digital to analog converters (DACs)
+ </listitem>
+ <listitem>
+ gyroscopes
+ </listitem>
+ <listitem>
+ inertial measurement units (IMUs)
+ </listitem>
+ <listitem>
+ color and light sensors
+ </listitem>
+ <listitem>
+ magnetometers
+ </listitem>
+ <listitem>
+ pressure sensors
+ </listitem>
+ <listitem>
+ proximity sensors
+ </listitem>
+ <listitem>
+ temperature sensors
+ </listitem>
+ </itemizedlist>
+ Usually these sensors are connected via SPI or I2C. It is also a common
+ use case to have combo functionality (e.g. light plus proximity sensor).
+ </para>
+ </chapter>
+ <chapter id='iiosubsys'>
+ <title>Industrial I/O core</title>
+ <para>
+ The Industrial I/O core offers:
+ <itemizedlist>
+ <listitem>
+ a unified framework for writing drivers for many different types of
+ embedded sensors.
+ </listitem>
+ <listitem>
+ a standard interface to user space applications manipulating sensors.
+ </listitem>
+ </itemizedlist>
+ The implementation can be found under <filename>
+ drivers/iio/industrialio-*</filename>
+ </para>
+ <sect1 id="iiodevice">
+ <title> Industrial I/O devices </title>
+
+!Finclude/linux/iio/iio.h iio_dev
+!Fdrivers/iio/industrialio-core.c iio_device_alloc
+!Fdrivers/iio/industrialio-core.c iio_device_free
+!Fdrivers/iio/industrialio-core.c iio_device_register
+!Fdrivers/iio/industrialio-core.c iio_device_unregister
+
+ <para>
+ 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.
+ </para>
+ <para>
+ There are two ways for a user space application to interact
+ with an IIO driver.
+ <itemizedlist>
+ <listitem>
+ <filename>/sys/bus/iio/iio:deviceX/</filename>, this
+ represents a hardware sensor and groups together the data
+ channels of the same chip.
+ </listitem>
+ <listitem>
+ <filename>/dev/iio:deviceX</filename>, character device node
+ interface used for faster data transfer and for events information
+ retrieval.
+ </listitem>
+ </itemizedlist>
+ </para>
+ A typical IIO driver will register itself as an I2C or SPI driver and will
+ create two routines, <function> probe </function> and <function> remove
+ </function>. At <function>probe</function>:
+ <itemizedlist>
+ <listitem>call <function>iio_device_alloc</function>, which allocates memory
+ for an IIO device.
+ </listitem>
+ <listitem> initialize IIO device fields with driver specific information
+ (e.g. device name, device channels).
+ </listitem>
+ <listitem>call <function> iio_device_register</function>, this registers the
+ device with the IIO core. After this call the device is ready to accept
+ requests from user space applications.
+ </listitem>
+ </itemizedlist>
+ At <function>remove</function>, we free the resources allocated in
+ <function>probe</function> in reverse order:
+ <itemizedlist>
+ <listitem><function>iio_device_unregister</function>, unregister the device
+ from the IIO core.
+ </listitem>
+ <listitem><function>iio_device_free</function>, free the memory allocated
+ for the IIO device.
+ </listitem>
+ </itemizedlist>
+
+ <sect2 id="iioattr"> <title> IIO device sysfs interface </title>
+ <para>
+ 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
+ <filename>/sys/bus/iio/iio:deviceX/ </filename> directory.
+ Common attributes are:
+ <itemizedlist>
+ <listitem><filename>name</filename>, description of the physical
+ chip.
+ </listitem>
+ <listitem><filename>dev</filename>, shows the major:minor pair
+ associated with <filename>/dev/iio:deviceX</filename> node.
+ </listitem>
+ <listitem><filename>sampling_frequency_available</filename>,
+ available discrete set of sampling frequency values for
+ device.
+ </listitem>
+ </itemizedlist>
+ Available standard attributes for IIO devices are described in the
+ <filename>Documentation/ABI/testing/sysfs-bus-iio </filename> file
+ in the Linux kernel sources.
+ </para>
+ </sect2>
+ <sect2 id="iiochannel"> <title> IIO device channels </title>
+!Finclude/linux/iio/iio.h iio_chan_spec structure.
+ <para>
+ An IIO device channel is a representation of a data channel. An
+ IIO device can have one or multiple channels. For example:
+ <itemizedlist>
+ <listitem>
+ a thermometer sensor has one channel representing the
+ temperature measurement.
+ </listitem>
+ <listitem>
+ a light sensor with two channels indicating the measurements in
+ the visible and infrared spectrum.
+ </listitem>
+ <listitem>
+ an accelerometer can have up to 3 channels representing
+ acceleration on X, Y and Z axes.
+ </listitem>
+ </itemizedlist>
+ An IIO channel is described by the <type> struct iio_chan_spec
+ </type>. A thermometer driver for the temperature sensor in the
+ example above would have to describe its channel as follows:
+ <programlisting>
+ static const struct iio_chan_spec temp_channel[] = {
+ {
+ .type = IIO_TEMP,
+ .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
+ },
+ };
+
+ </programlisting>
+ Channel sysfs attributes exposed to userspace are specified in
+ the form of <emphasis>bitmasks</emphasis>. Depending on their
+ shared info, attributes can be set in one of the following masks:
+ <itemizedlist>
+ <listitem><emphasis>info_mask_separate</emphasis>, attributes will
+ be specific to this channel</listitem>
+ <listitem><emphasis>info_mask_shared_by_type</emphasis>,
+ attributes are shared by all channels of the same type</listitem>
+ <listitem><emphasis>info_mask_shared_by_dir</emphasis>, attributes
+ are shared by all channels of the same direction </listitem>
+ <listitem><emphasis>info_mask_shared_by_all</emphasis>,
+ attributes are shared by all channels</listitem>
+ </itemizedlist>
+ When there are multiple data channels per sensor type there are two
+ ways to distinguish between them:
+ <itemizedlist>
+ <listitem> set <emphasis> .modified</emphasis> field of <type>
+ iio_chan_spec</type> to 1. Modifiers are specified using
+ <emphasis>.channel2</emphasis> field of the same
+ <type>iio_chan_spec</type> 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.
+ </listitem>
+ <listitem> set <emphasis>.indexed </emphasis> field of
+ <type>iio_chan_spec</type> to 1. In this case the channel is
+ simply another instance with an index specified by the
+ <emphasis>.channel</emphasis> field.
+ </listitem>
+ </itemizedlist>
+ Here is how we can make use of the channel's modifiers:
+ <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),
+ },
+
+ }
+ </programlisting>
+ This channel's definition will generate two separate sysfs files
+ for raw data retrieval:
+ <itemizedlist>
+ <listitem>
+ <filename>/sys/bus/iio/iio:deviceX/in_intensity_ir_raw</filename>
+ </listitem>
+ <listitem>
+ <filename>/sys/bus/iio/iio:deviceX/in_intensity_both_raw</filename>
+ </listitem>
+ </itemizedlist>
+ one file for processed data:
+ <itemizedlist>
+ <listitem>
+ <filename>/sys/bus/iio/iio:deviceX/in_illuminance_input
+ </filename>
+ </listitem>
+ </itemizedlist>
+ and one shared sysfs file for sampling frequency:
+ <itemizedlist>
+ <listitem>
+ <filename>/sys/bus/iio/iio:deviceX/in_intensity_sampling_frequency.
+ </filename>
+ </listitem>
+ </itemizedlist>
+ </para>
+ <para>
+ Here is how we can make use of the channel's indexing:
+ <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),
+ },
+ }
+ </programlisting>
+ This will generate two separate attributes files for raw data
+ retrieval:
+ <itemizedlist>
+ <listitem>
+ <filename>/sys/bus/iio/devices/iio:deviceX/in_voltage0_raw</filename>,
+ representing voltage measurement for channel 0.
+ </listitem>
+ <listitem>
+ <filename>/sys/bus/iio/devices/iio:deviceX/in_voltage1_raw</filename>,
+ representing voltage measurement for channel 1.
+ </listitem>
+ </itemizedlist>
+ </para>
+ </sect2>
+ </sect1>
+
+ <sect1 id="iiobuffer"> <title> Industrial I/O buffers </title>
+!Finclude/linux/iio/buffer.h iio_buffer
+!Edrivers/iio/industrialio-buffer.c
+
+ <para>
+ The Industrial I/O core offers a way for continuous data capture
+ based on a trigger source. Multiple data channels can be read at once
+ from <filename>/dev/iio:deviceX</filename> character device node,
+ thus reducing the CPU load.
+ </para>
+
+ <sect2 id="iiobuffersysfs">
+ <title>IIO buffer sysfs interface </title>
+ <para>
+ An IIO buffer has an associated attributes directory under <filename>
+ /sys/bus/iio/iio:deviceX/buffer/</filename>. Here are the existing
+ attributes:
+ <itemizedlist>
+ <listitem>
+ <emphasis>length</emphasis>, number of data samples contained by the
+ buffer.
+ </listitem>
+ <listitem>
+ <emphasis>enable</emphasis>, activate buffer capture.
+ </listitem>
+ </itemizedlist>
+ </para>
+ </sect2>
+ <sect2 id="iiobuffersetup"> <title> IIO buffer setup </title>
+ <para>The meta information associated with a channel reading
+ placed in a buffer is called a <emphasis> scan element </emphasis>.
+ The important bits configuring scan elements are exposed to
+ userspace applications via the <filename>
+ /sys/bus/iio/iio:deviceX/scan_elements/</filename> directory. This
+ file contains attributes of the following form:
+ <itemizedlist>
+ <listitem><emphasis>enable</emphasis>, used for enabling a channel.
+ If and only if its attribute is non zero, then a triggered capture
+ will contain data samples for this channel.
+ </listitem>
+ <listitem><emphasis>type</emphasis>, description of the scan element
+ data storage within the buffer and hence the form in which it is
+ read from user space. Format is <emphasis>
+ [be|le]:[s|u]bits/storagebitsXrepeat[>>shift] </emphasis>.
+ <itemizedlist>
+ <listitem> <emphasis>be</emphasis> or <emphasis>le</emphasis> specifies
+ big or little endian.
+ </listitem>
+ <listitem>
+ <emphasis>s </emphasis>or <emphasis>u</emphasis> specifies if
+ signed (2's complement) or unsigned.
+ </listitem>
+ <listitem><emphasis>bits</emphasis> is the number of bits of data
+ </listitem>
+ <listitem><emphasis>storagebits</emphasis> is the space (after padding)
+ that it occupies in the buffer.
+ </listitem>
+ <listitem>
+ <emphasis>shift</emphasis> if specified, is the shift that needs
+ to be a applied prior to masking out unused bits
+ </listitem>
+ <listitem>
+ <emphasis>repeat</emphasis>, specifies the number of real/storage bits
+ repetitions. When the repeat element is 0 or 1, then the repeat
+ value is omitted.
+ </listitem>
+ </itemizedlist>
+ </listitem>
+ </itemizedlist>
+ For example, a driver for a 3-axis accelerometer with 12 bit
+ resolution where data is stored in two 8-bits registers as
+ follows:
+ <programlisting>
+ 7 6 5 4 3 2 1 0
+ +---+---+---+---+---+---+---+---+
+ |D3 |D2 |D1 |D0 | X | X | X | X | (LOW byte, address 0x06)
+ +---+---+---+---+---+---+---+---+
+
+ 7 6 5 4 3 2 1 0
+ +---+---+---+---+---+---+---+---+
+ |D11|D10|D9 |D8 |D7 |D6 |D5 |D4 | (HIGH byte, address 0x07)
+ +---+---+---+---+---+---+---+---+
+ </programlisting>
+
+ will have the following scan element type for each axis:
+ <programlisting>
+ $ cat /sys/bus/iio/devices/iio:device0/scan_elements/in_accel_y_type
+ le:s12/16>>4
+ </programlisting>
+ The userspace applications will interpret data samples read from buffer
+ as two byte little endian signed data, that needs a 4 bits right
+ shift before masking out the only 12 valid bits of real data.
+ </para>
+ <para>
+ For implementing buffer support a driver should initialize the following
+ fields in <type>iio_chan_spec</type> definition:
+ <programlisting>
+ struct iio_chan_spec {
+ /* other members */
+ int scan_index
+ struct {
+ char sign;
+ u8 realbits;
+ u8 storagebits;
+ u8 shift;
+ u8 repeat;
+ enum iio_endian endianness;
+ } scan_type;
+ };
+ </programlisting>
+ The driver implementing the accelerometer described above will
+ have the following channel definition:
+ <programlisting>
+ struct struct iio_chan_spec accel_channels[] = {
+ {
+ .type = IIO_ACCEL,
+ .modified = 1,
+ .channel2 = IIO_MOD_X,
+ /* other stuff here */
+ .scan_index = 0,
+ .scan_type = {
+ .sign = 's',
+ .realbits = 12,
+ .storgebits = 16,
+ .shift = 4,
+ .endianness = IIO_LE,
+ },
+ }
+ /* similar for Y and Z axis */
+ }
+ </programlisting>
+ </para>
+ <para>
+ Here <emphasis> scan_index </emphasis> defines the relative order in which
+ the enabled channels are placed inside the buffer, a channel with a lower
+ scan_index will be placed before a channel with a higher index. Each
+ channels needs to have a unique scan_index.
+ </para>
+ <para>
+ It is important to realize that the scan_index does not define the
+ absolution position in the buffer. E.g. a channel with the scan_index = 3
+ will not be at offset 3 bytes or 3 words, but rather will be placed in the
+ buffer after any channel with a scan_index lower than 3 and before
+ any channel with a scan_index larger than 3.
+ Furthermore the scan indices do not have to be consecutive. E.g. A
+ channel spec array that defines 3 channels with the indices 1, 2 and 3 is
+ just as valid as a channel spec that uses the indices 100, 200, 300. The
+ relative order of the channels will be the same.
+ </para>
+ <para>
+ Setting scan_index to -1 can be used to indicate that the specific
+ channel does not support buffered capture. In this case no entries will
+ be created for the channel in the scan_elements directory.
+ </para>
+ </sect2>
+ </sect1>
+
+ <sect1 id="iiotrigger"> <title> Industrial I/O triggers </title>
+!Finclude/linux/iio/trigger.h iio_trigger
+!Edrivers/iio/industrialio-trigger.c
+ <para>
+ In many situations it is useful for a driver to be able to
+ capture data based on some external event (trigger) as opposed
+ to periodically polling for data. An IIO trigger can be provided
+ by a device driver that also has an IIO device based on hardware
+ generated events (e.g. data ready or threshold exceeded) or
+ provided by a separate driver from an independent interrupt
+ source (e.g. GPIO line connected to some external system, timer
+ interrupt or user space reading a specific file in sysfs). A
+ trigger may initialize data capture for a number of sensors and
+ also it may be completely unrelated to the sensor itself.
+ </para>
+
+ <sect2 id="iiotrigsysfs"> <title> IIO trigger sysfs interface </title>
+ There are two locations in sysfs related to triggers:
+ <itemizedlist>
+ <listitem><filename>/sys/bus/iio/devices/triggerX</filename>,
+ this file is created once an IIO triggered is registered with
+ the IIO core and corresponds to trigger with index X. Because
+ triggers can be very different depending on type there are few
+ standard attributes that we can describe here:
+ <itemizedlist>
+ <listitem>
+ <emphasis>name</emphasis>, trigger name that can be later
+ used to for association with a device.
+ </listitem>
+ <listitem>
+ <emphasis>sampling_frequency</emphasis>, some timer based
+ triggers use this attribute to specify the frequency for
+ trigger calls.
+ </listitem>
+ </itemizedlist>
+ </listitem>
+ <listitem>
+ <filename>/sys/bus/iio/devices/iio:deviceX/trigger/</filename>, this
+ directory is created once the device supports a triggered
+ buffer. We can associate a trigger with our device by writing
+ trigger's name in the<filename>current_trigger</filename> file.
+ </listitem>
+ </itemizedlist>
+ </sect2>
+
+ <sect2 id="iiotrigattr"> <title> IIO trigger setup</title>
+
+ <para>
+ Let's see a simple example of how to setup a trigger to be used
+ by a driver.
+
+ <programlisting>
+ struct iio_trigger_ops trigger_ops = {
+ .set_trigger_state = sample_trigger_state,
+ .validate_device = sample_validate_device,
+ }
+
+ struct iio_trigger *trig;
+
+ /* first, allocate memory for our trigger */
+ trig = iio_trigger_alloc(dev, "trig-%s-%d", name, idx);
+
+ /* setup trigger operations field */
+ trig->ops = &trigger_ops;
+
+ /* now register the trigger with the IIO core */
+ iio_trigger_register(trig);
+ </programlisting>
+ </para>
+ </sect2>
+
+ <sect2 id="iiotrigsetup"> <title> IIO trigger ops</title>
+!Finclude/linux/iio/trigger.h iio_trigger_ops
+ <para>
+ Notice that a trigger has a set of operations attached:
+ <itemizedlist>
+ <listitem>
+ <function>set_trigger_state</function>, switch the trigger on/off
+ on demand.
+ </listitem>
+ <listitem>
+ <function>validate_device</function>, function to validate the
+ device when the current trigger gets changed.
+ </listitem>
+ </itemizedlist>
+ </para>
+ </sect2>
+ </sect1>
+ <sect1 id="iiotriggered_buffer">
+ <title> Industrial I/O triggered buffers </title>
+ <para>
+ Now that we know what buffers and triggers are let's see how they
+ work together.
+ </para>
+ <sect2 id="iiotrigbufsetup"> <title> IIO triggered buffer setup</title>
+!Edrivers/iio/industrialio-triggered-buffer.c
+!Finclude/linux/iio/iio.h iio_buffer_setup_ops
+
+
+ <para>
+ A typical triggered buffer setup looks like this:
+ <programlisting>
+ const struct iio_buffer_setup_ops sensor_buffer_setup_ops = {
+ .preenable = sensor_buffer_preenable,
+ .postenable = sensor_buffer_postenable,
+ .postdisable = sensor_buffer_postdisable,
+ .predisable = sensor_buffer_predisable,
+ };
+
+ irqreturn_t sensor_iio_pollfunc(int irq, void *p)
+ {
+ pf->timestamp = iio_get_time_ns();
+ return IRQ_WAKE_THREAD;
+ }
+
+ irqreturn_t sensor_trigger_handler(int irq, void *p)
+ {
+ u16 buf[8];
+
+ /* read data for each active channel */
+ for_each_set_bit(bit, active_scan_mask, masklength)
+ buf[i++] = sensor_get_data(bit)
+
+ iio_push_to_buffers_with_timestamp(indio_dev, buffer, timestamp);
+
+ iio_trigger_notify_done(trigger);
+ }
+
+ /* setup triggered buffer, usually in probe function */
+ iio_triggered_buffer_setup(indio_dev, sensor_iio_polfunc,
+ sensor_trigger_handler,
+ sensor_buffer_setup_ops);
+ </programlisting>
+ </para>
+ The important things to notice here are:
+ <itemizedlist>
+ <listitem><function> iio_buffer_setup_ops</function>, the buffer setup
+ functions to be called at predefined points in buffer configuration
+ sequence (e.g. before enable, after disable). If not specified, the
+ IIO core uses the default <type>iio_triggered_buffer_setup_ops</type>.
+ </listitem>
+ <listitem><function>sensor_iio_pollfunc</function>, the function that
+ will be used as top half of poll function. It usually does little
+ processing (as it runs in interrupt context). The most common operation
+ is recording of the current timestamp and for this reason one can
+ use the IIO core defined <function>iio_pollfunc_store_time</function>
+ function.
+ </listitem>
+ <listitem><function>sensor_trigger_handler</function>, the function that
+ will be used as bottom half of the poll function. This runs in the
+ context of a kernel thread and all the processing takes place here.
+ It usually reads data from the device and stores it in the internal
+ buffer together with the timestamp recorded in the top half.
+ </listitem>
+ </itemizedlist>
+ </sect2>
+ </sect1>
+ </chapter>
+ <chapter id='iioresources'>
+ <title> Resources </title>
+ IIO core may change during time so the best documentation to read is the
+ source code. There are several locations where you should look:
+ <itemizedlist>
+ <listitem>
+ <filename>drivers/iio/</filename>, contains the IIO core plus
+ and directories for each sensor type (e.g. accel, magnetometer,
+ etc.)
+ </listitem>
+ <listitem>
+ <filename>include/linux/iio/</filename>, contains the header
+ files, nice to read for the internal kernel interfaces.
+ </listitem>
+ <listitem>
+ <filename>include/uapi/linux/iio/</filename>, contains files to be
+ used by user space applications.
+ </listitem>
+ <listitem>
+ <filename>tools/iio/</filename>, contains tools for rapidly
+ testing buffers, events and device creation.
+ </listitem>
+ <listitem>
+ <filename>drivers/staging/iio/</filename>, contains code for some
+ drivers or experimental features that are not yet mature enough
+ to be moved out.
+ </listitem>
+ </itemizedlist>
+ <para>
+ Besides the code, there are some good online documentation sources:
+ <itemizedlist>
+ <listitem>
+ <ulink url="http://marc.info/?l=linux-iio"> Industrial I/O mailing
+ list </ulink>
+ </listitem>
+ <listitem>
+ <ulink url="http://wiki.analog.com/software/linux/docs/iio/iio">
+ Analog Device IIO wiki page </ulink>
+ </listitem>
+ <listitem>
+ <ulink url="https://fosdem.org/2015/schedule/event/iiosdr/">
+ Using the Linux IIO framework for SDR, Lars-Peter Clausen's
+ presentation at FOSDEM </ulink>
+ </listitem>
+ </itemizedlist>
+ </para>
+ </chapter>
+</book>
+
+<!--
+vim: softtabstop=2:shiftwidth=2:expandtab:textwidth=72
+-->
--
1.9.1
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