1<refentry id="vidioc-streamon"> 2 <refmeta> 3 <refentrytitle>ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF</refentrytitle> 4 &manvol; 5 </refmeta> 6 7 <refnamediv> 8 <refname>VIDIOC_STREAMON</refname> 9 <refname>VIDIOC_STREAMOFF</refname> 10 <refpurpose>Start or stop streaming I/O</refpurpose> 11 </refnamediv> 12 13 <refsynopsisdiv> 14 <funcsynopsis> 15 <funcprototype> 16 <funcdef>int <function>ioctl</function></funcdef> 17 <paramdef>int <parameter>fd</parameter></paramdef> 18 <paramdef>int <parameter>request</parameter></paramdef> 19 <paramdef>const int *<parameter>argp</parameter></paramdef> 20 </funcprototype> 21 </funcsynopsis> 22 </refsynopsisdiv> 23 24 <refsect1> 25 <title>Arguments</title> 26 27 <variablelist> 28 <varlistentry> 29 <term><parameter>fd</parameter></term> 30 <listitem> 31 <para>&fd;</para> 32 </listitem> 33 </varlistentry> 34 <varlistentry> 35 <term><parameter>request</parameter></term> 36 <listitem> 37 <para>VIDIOC_STREAMON, VIDIOC_STREAMOFF</para> 38 </listitem> 39 </varlistentry> 40 <varlistentry> 41 <term><parameter>argp</parameter></term> 42 <listitem> 43 <para></para> 44 </listitem> 45 </varlistentry> 46 </variablelist> 47 </refsect1> 48 49 <refsect1> 50 <title>Description</title> 51 52 <para>The <constant>VIDIOC_STREAMON</constant> and 53<constant>VIDIOC_STREAMOFF</constant> ioctl start and stop the capture 54or output process during streaming (<link linkend="mmap">memory 55mapping</link> or <link linkend="userp">user pointer</link>) I/O.</para> 56 57 <para>Specifically the capture hardware is disabled and no input 58buffers are filled (if there are any empty buffers in the incoming 59queue) until <constant>VIDIOC_STREAMON</constant> has been called. 60Accordingly the output hardware is disabled, no video signal is 61produced until <constant>VIDIOC_STREAMON</constant> has been called. 62The ioctl will succeed only when at least one output buffer is in the 63incoming queue.</para> 64 65 <para>The <constant>VIDIOC_STREAMOFF</constant> ioctl, apart of 66aborting or finishing any DMA in progress, unlocks any user pointer 67buffers locked in physical memory, and it removes all buffers from the 68incoming and outgoing queues. That means all images captured but not 69dequeued yet will be lost, likewise all images enqueued for output but 70not transmitted yet. I/O returns to the same state as after calling 71&VIDIOC-REQBUFS; and can be restarted accordingly.</para> 72 73 <para>Both ioctls take a pointer to an integer, the desired buffer or 74stream type. This is the same as &v4l2-requestbuffers; 75<structfield>type</structfield>.</para> 76 77 <para>Note applications can be preempted for unknown periods right 78before or after the <constant>VIDIOC_STREAMON</constant> or 79<constant>VIDIOC_STREAMOFF</constant> calls, there is no notion of 80starting or stopping "now". Buffer timestamps can be used to 81synchronize with other events.</para> 82 </refsect1> 83 84 <refsect1> 85 &return-value; 86 87 <variablelist> 88 <varlistentry> 89 <term><errorcode>EINVAL</errorcode></term> 90 <listitem> 91 <para>Streaming I/O is not supported, the buffer 92<structfield>type</structfield> is not supported, or no buffers have 93been allocated (memory mapping) or enqueued (output) yet.</para> 94 </listitem> 95 </varlistentry> 96 </variablelist> 97 </refsect1> 98</refentry> 99 100<!-- 101Local Variables: 102mode: sgml 103sgml-parent-document: "v4l2.sgml" 104indent-tabs-mode: nil 105End: 106--> 107