forked from luck/tmp_suning_uos_patched
8e080c2e6c
The V4L and DVB API's are there for a long time. however, up to now, no efforts were done to merge them to kernel DocBook. This patch adds the current versions of the specs as an unique compendium. Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
107 lines
3.3 KiB
XML
107 lines
3.3 KiB
XML
<refentry id="vidioc-streamon">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_STREAMON</refname>
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<refname>VIDIOC_STREAMOFF</refname>
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<refpurpose>Start or stop streaming I/O</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>const int *<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_STREAMON, VIDIOC_STREAMOFF</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>The <constant>VIDIOC_STREAMON</constant> and
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<constant>VIDIOC_STREAMOFF</constant> ioctl start and stop the capture
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or output process during streaming (<link linkend="mmap">memory
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mapping</link> or <link linkend="userp">user pointer</link>) I/O.</para>
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<para>Specifically the capture hardware is disabled and no input
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buffers are filled (if there are any empty buffers in the incoming
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queue) until <constant>VIDIOC_STREAMON</constant> has been called.
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Accordingly the output hardware is disabled, no video signal is
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produced until <constant>VIDIOC_STREAMON</constant> has been called.
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The ioctl will succeed only when at least one output buffer is in the
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incoming queue.</para>
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<para>The <constant>VIDIOC_STREAMOFF</constant> ioctl, apart of
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aborting or finishing any DMA in progress, unlocks any user pointer
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buffers locked in physical memory, and it removes all buffers from the
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incoming and outgoing queues. That means all images captured but not
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dequeued yet will be lost, likewise all images enqueued for output but
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not transmitted yet. I/O returns to the same state as after calling
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&VIDIOC-REQBUFS; and can be restarted accordingly.</para>
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<para>Both ioctls take a pointer to an integer, the desired buffer or
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stream type. This is the same as &v4l2-requestbuffers;
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<structfield>type</structfield>.</para>
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<para>Note applications can be preempted for unknown periods right
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before or after the <constant>VIDIOC_STREAMON</constant> or
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<constant>VIDIOC_STREAMOFF</constant> calls, there is no notion of
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starting or stopping "now". Buffer timestamps can be used to
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synchronize with other events.</para>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>Streaming I/O is not supported, the buffer
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<structfield>type</structfield> is not supported, or no buffers have
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been allocated (memory mapping) or enqueued (output) yet.</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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</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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