V4L/DVB: V4L: Events: Add documentation
Add documentation on how to use V4L2 events, both for V4L2 drivers and for V4L2 applications. Signed-off-by: Sakari Ailus <sakari.ailus@maxwell.research.nokia.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Sakari Ailus
Mauro Carvalho Chehab
Родитель
d3d7c96356
Коммит
dd96608369
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@ -17,6 +17,7 @@
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<!ENTITY VIDIOC-DBG-G-REGISTER "<link linkend='vidioc-dbg-g-register'><constant>VIDIOC_DBG_G_REGISTER</constant></link>">
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<!ENTITY VIDIOC-DBG-S-REGISTER "<link linkend='vidioc-dbg-g-register'><constant>VIDIOC_DBG_S_REGISTER</constant></link>">
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<!ENTITY VIDIOC-DQBUF "<link linkend='vidioc-qbuf'><constant>VIDIOC_DQBUF</constant></link>">
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<!ENTITY VIDIOC-DQEVENT "<link linkend='vidioc-dqevent'><constant>VIDIOC_DQEVENT</constant></link>">
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<!ENTITY VIDIOC-ENCODER-CMD "<link linkend='vidioc-encoder-cmd'><constant>VIDIOC_ENCODER_CMD</constant></link>">
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<!ENTITY VIDIOC-ENUMAUDIO "<link linkend='vidioc-enumaudio'><constant>VIDIOC_ENUMAUDIO</constant></link>">
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<!ENTITY VIDIOC-ENUMAUDOUT "<link linkend='vidioc-enumaudioout'><constant>VIDIOC_ENUMAUDOUT</constant></link>">
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@ -60,6 +61,7 @@
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<!ENTITY VIDIOC-REQBUFS "<link linkend='vidioc-reqbufs'><constant>VIDIOC_REQBUFS</constant></link>">
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<!ENTITY VIDIOC-STREAMOFF "<link linkend='vidioc-streamon'><constant>VIDIOC_STREAMOFF</constant></link>">
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<!ENTITY VIDIOC-STREAMON "<link linkend='vidioc-streamon'><constant>VIDIOC_STREAMON</constant></link>">
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<!ENTITY VIDIOC-SUBSCRIBE-EVENT "<link linkend='vidioc-subscribe-event'><constant>VIDIOC_SUBSCRIBE_EVENT</constant></link>">
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<!ENTITY VIDIOC-S-AUDIO "<link linkend='vidioc-g-audio'><constant>VIDIOC_S_AUDIO</constant></link>">
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<!ENTITY VIDIOC-S-AUDOUT "<link linkend='vidioc-g-audioout'><constant>VIDIOC_S_AUDOUT</constant></link>">
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<!ENTITY VIDIOC-S-CROP "<link linkend='vidioc-g-crop'><constant>VIDIOC_S_CROP</constant></link>">
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@ -141,6 +143,8 @@
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<!ENTITY v4l2-enc-idx "struct <link linkend='v4l2-enc-idx'>v4l2_enc_idx</link>">
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<!ENTITY v4l2-enc-idx-entry "struct <link linkend='v4l2-enc-idx-entry'>v4l2_enc_idx_entry</link>">
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<!ENTITY v4l2-encoder-cmd "struct <link linkend='v4l2-encoder-cmd'>v4l2_encoder_cmd</link>">
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<!ENTITY v4l2-event "struct <link linkend='v4l2-event'>v4l2_event</link>">
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<!ENTITY v4l2-event-subscription "struct <link linkend='v4l2-event-subscription'>v4l2_event_subscription</link>">
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<!ENTITY v4l2-ext-control "struct <link linkend='v4l2-ext-control'>v4l2_ext_control</link>">
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<!ENTITY v4l2-ext-controls "struct <link linkend='v4l2-ext-controls'>v4l2_ext_controls</link>">
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<!ENTITY v4l2-fmtdesc "struct <link linkend='v4l2-fmtdesc'>v4l2_fmtdesc</link>">
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@ -200,6 +204,7 @@
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<!ENTITY sub-controls SYSTEM "v4l/controls.xml">
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<!ENTITY sub-dev-capture SYSTEM "v4l/dev-capture.xml">
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<!ENTITY sub-dev-codec SYSTEM "v4l/dev-codec.xml">
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<!ENTITY sub-dev-event SYSTEM "v4l/dev-event.xml">
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<!ENTITY sub-dev-effect SYSTEM "v4l/dev-effect.xml">
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<!ENTITY sub-dev-osd SYSTEM "v4l/dev-osd.xml">
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<!ENTITY sub-dev-output SYSTEM "v4l/dev-output.xml">
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@ -292,6 +297,8 @@
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<!ENTITY sub-v4l2grab-c SYSTEM "v4l/v4l2grab.c.xml">
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<!ENTITY sub-videodev2-h SYSTEM "v4l/videodev2.h.xml">
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<!ENTITY sub-v4l2 SYSTEM "v4l/v4l2.xml">
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<!ENTITY sub-dqevent SYSTEM "v4l/vidioc-dqevent.xml">
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<!ENTITY sub-subscribe-event SYSTEM "v4l/vidioc-subscribe-event.xml">
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<!ENTITY sub-intro SYSTEM "dvb/intro.xml">
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<!ENTITY sub-frontend SYSTEM "dvb/frontend.xml">
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<!ENTITY sub-dvbproperty SYSTEM "dvb/dvbproperty.xml">
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@ -381,3 +388,5 @@
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<!ENTITY reqbufs SYSTEM "v4l/vidioc-reqbufs.xml">
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<!ENTITY s-hw-freq-seek SYSTEM "v4l/vidioc-s-hw-freq-seek.xml">
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<!ENTITY streamon SYSTEM "v4l/vidioc-streamon.xml">
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<!ENTITY dqevent SYSTEM "v4l/vidioc-dqevent.xml">
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<!ENTITY subscribe_event SYSTEM "v4l/vidioc-subscribe-event.xml">
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@ -0,0 +1,31 @@
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<title>Event Interface</title>
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<para>The V4L2 event interface provides means for user to get
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immediately notified on certain conditions taking place on a device.
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This might include start of frame or loss of signal events, for
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example.
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</para>
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<para>To receive events, the events the user is interested in first must
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be subscribed using the &VIDIOC-SUBSCRIBE-EVENT; ioctl. Once an event is
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subscribed, the events of subscribed types are dequeueable using the
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&VIDIOC-DQEVENT; ioctl. Events may be unsubscribed using
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VIDIOC_UNSUBSCRIBE_EVENT ioctl. The special event type V4L2_EVENT_ALL may
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be used to unsubscribe all the events the driver supports.</para>
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<para>The event subscriptions and event queues are specific to file
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handles. Subscribing an event on one file handle does not affect
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other file handles.
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</para>
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<para>The information on dequeueable events is obtained by using select or
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poll system calls on video devices. The V4L2 events use POLLPRI events on
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poll system call and exceptions on select system call. </para>
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<!--
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Local Variables:
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mode: sgml
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sgml-parent-document: "v4l2.sgml"
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indent-tabs-mode: nil
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End:
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-->
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@ -401,6 +401,7 @@ and discussions on the V4L mailing list.</revremark>
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<section id="ttx"> &sub-dev-teletext; </section>
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<section id="radio"> &sub-dev-radio; </section>
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<section id="rds"> &sub-dev-rds; </section>
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<section id="event"> &sub-dev-event; </section>
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</chapter>
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<chapter id="driver">
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@ -426,6 +427,7 @@ and discussions on the V4L mailing list.</revremark>
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&sub-cropcap;
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&sub-dbg-g-chip-ident;
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&sub-dbg-g-register;
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&sub-dqevent;
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&sub-encoder-cmd;
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&sub-enumaudio;
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&sub-enumaudioout;
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@ -467,6 +469,7 @@ and discussions on the V4L mailing list.</revremark>
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&sub-reqbufs;
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&sub-s-hw-freq-seek;
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&sub-streamon;
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&sub-subscribe-event;
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<!-- End of ioctls. -->
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&sub-mmap;
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&sub-munmap;
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@ -0,0 +1,124 @@
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<refentry id="vidioc-dqevent">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_DQEVENT</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_DQEVENT</refname>
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<refpurpose>Dequeue event</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_event
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*<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_DQEVENT</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>Dequeue an event from a video device. No input is required
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for this ioctl. All the fields of the &v4l2-event; structure are
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filled by the driver. The file handle will also receive exceptions
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which the application may get by e.g. using the select system
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call.</para>
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<table frame="none" pgwide="1" id="v4l2-event">
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<title>struct <structname>v4l2_event</structname></title>
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<tgroup cols="4">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>type</structfield></entry>
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<entry></entry>
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<entry>Type of the event.</entry>
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</row>
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<row>
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<entry>union</entry>
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<entry><structfield>u</structfield></entry>
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<entry></entry>
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<entry></entry>
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</row>
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<row>
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<entry></entry>
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<entry>__u8</entry>
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<entry><structfield>data</structfield>[64]</entry>
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<entry>Event data. Defined by the event type. The union
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should be used to define easily accessible type for
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events.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>pending</structfield></entry>
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<entry></entry>
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<entry>Number of pending events excluding this one.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>sequence</structfield></entry>
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<entry></entry>
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<entry>Event sequence number. The sequence number is
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incremented for every subscribed event that takes place.
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If sequence numbers are not contiguous it means that
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events have been lost.
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</entry>
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</row>
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<row>
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<entry>struct timeval</entry>
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<entry><structfield>timestamp</structfield></entry>
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<entry></entry>
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<entry>Event timestamp.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield>[9]</entry>
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<entry></entry>
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<entry>Reserved for future extensions. Drivers must set
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the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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</refentry>
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<!--
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Local Variables:
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mode: sgml
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sgml-parent-document: "v4l2.sgml"
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indent-tabs-mode: nil
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End:
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-->
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@ -0,0 +1,104 @@
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<refentry id="vidioc-subscribe-event">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT</refname>
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<refpurpose>Subscribe or unsubscribe event</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_event_subscription
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*<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>Subscribe or unsubscribe V4L2 event. Subscribed events are
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dequeued by using the &VIDIOC-DQEVENT; ioctl.</para>
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<table frame="none" pgwide="1" id="v4l2-event-subscription">
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<title>struct <structname>v4l2_event_subscription</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>type</structfield></entry>
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<entry>Type of the event.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield>[7]</entry>
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<entry>Reserved for future extensions. Drivers and applications
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must set the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table frame="none" pgwide="1" id="event-type">
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<title>Event Types</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_EVENT_ALL</constant></entry>
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<entry>0</entry>
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<entry>All events. V4L2_EVENT_ALL is valid only for
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VIDIOC_UNSUBSCRIBE_EVENT for unsubscribing all events at once.
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</entry>
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</row>
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<row>
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<entry><constant>V4L2_EVENT_PRIVATE_START</constant></entry>
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<entry>0x08000000</entry>
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<entry>Base event number for driver-private events.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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</refentry>
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<!--
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Local Variables:
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mode: sgml
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sgml-parent-document: "v4l2.sgml"
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indent-tabs-mode: nil
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End:
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-->
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@ -680,3 +680,63 @@ int my_release(struct file *file)
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...
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}
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V4L2 events
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-----------
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The V4L2 events provide a generic way to pass events to user space.
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The driver must use v4l2_fh to be able to support V4L2 events.
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Useful functions:
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- v4l2_event_alloc()
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To use events, the driver must allocate events for the file handle. By
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calling the function more than once, the driver may assure that at least n
|
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events in total have been allocated. The function may not be called in
|
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atomic context.
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- v4l2_event_queue()
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Queue events to video device. The driver's only responsibility is to fill
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in the type and the data fields. The other fields will be filled in by
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V4L2.
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- v4l2_event_subscribe()
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The video_device->ioctl_ops->vidioc_subscribe_event must check the driver
|
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is able to produce events with specified event id. Then it calls
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v4l2_event_subscribe() to subscribe the event.
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- v4l2_event_unsubscribe()
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vidioc_unsubscribe_event in struct v4l2_ioctl_ops. A driver may use
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v4l2_event_unsubscribe() directly unless it wants to be involved in
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unsubscription process.
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The special type V4L2_EVENT_ALL may be used to unsubscribe all events. The
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drivers may want to handle this in a special way.
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- v4l2_event_pending()
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Returns the number of pending events. Useful when implementing poll.
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Drivers do not initialise events directly. The events are initialised
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through v4l2_fh_init() if video_device->ioctl_ops->vidioc_subscribe_event is
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non-NULL. This *MUST* be performed in the driver's
|
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v4l2_file_operations->open() handler.
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Events are delivered to user space through the poll system call. The driver
|
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can use v4l2_fh->events->wait wait_queue_head_t as the argument for
|
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poll_wait().
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There are standard and private events. New standard events must use the
|
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smallest available event type. The drivers must allocate their events from
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their own class starting from class base. Class base is
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V4L2_EVENT_PRIVATE_START + n * 1000 where n is the lowest available number.
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The first event type in the class is reserved for future use, so the first
|
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available event type is 'class base + 1'.
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An example on how the V4L2 events may be used can be found in the OMAP
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3 ISP driver available at <URL:http://gitorious.org/omap3camera> as of
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writing this.
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