Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 EST.
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 54 or output process during streaming (<link linkend="mmap">memory 55 mapping</link>, <link linkend="userp">user pointer</link> or 56 <link linkend="dmabuf">DMABUF</link>) I/O.</para> 57 58 <para>Capture hardware is disabled and no input 59 buffers are filled (if there are any empty buffers in the incoming 60 queue) until <constant>VIDIOC_STREAMON</constant> has been called. 61 Output hardware is disabled and no video signal is 62 produced until <constant>VIDIOC_STREAMON</constant> has been called. 63 The ioctl will succeed when at least one output buffer is in the 64 incoming queue.</para> 65 66 <para>Memory-to-memory devices will not start until 67 <constant>VIDIOC_STREAMON</constant> has been called for both the capture 68 and output stream types.</para> 69 70 <para>If <constant>VIDIOC_STREAMON</constant> fails then any already 71 queued buffers will remain queued.</para> 72 73 <para>The <constant>VIDIOC_STREAMOFF</constant> ioctl, apart of 74 aborting or finishing any DMA in progress, unlocks any user pointer 75 buffers locked in physical memory, and it removes all buffers from the 76 incoming and outgoing queues. That means all images captured but not 77 dequeued yet will be lost, likewise all images enqueued for output but 78 not transmitted yet. I/O returns to the same state as after calling 79 &VIDIOC-REQBUFS; and can be restarted accordingly.</para> 80 81 <para>If buffers have been queued with &VIDIOC-QBUF; and 82 <constant>VIDIOC_STREAMOFF</constant> is called without ever having 83 called <constant>VIDIOC_STREAMON</constant>, then those queued buffers 84 will also be removed from the incoming queue and all are returned to the 85 same state as after calling &VIDIOC-REQBUFS; and can be restarted 86 accordingly.</para> 87 88 <para>Both ioctls take a pointer to an integer, the desired buffer or 89 stream type. This is the same as &v4l2-requestbuffers; 90 <structfield>type</structfield>.</para> 91 92 <para>If <constant>VIDIOC_STREAMON</constant> is called when streaming 93 is already in progress, or if <constant>VIDIOC_STREAMOFF</constant> is called 94 when streaming is already stopped, then 0 is returned. Nothing happens in the 95 case of <constant>VIDIOC_STREAMON</constant>, but <constant>VIDIOC_STREAMOFF</constant> 96 will return queued buffers to their starting state as mentioned above.</para> 97 98 <para>Note that applications can be preempted for unknown periods right 99 before or after the <constant>VIDIOC_STREAMON</constant> or 100 <constant>VIDIOC_STREAMOFF</constant> calls, there is no notion of 101 starting or stopping "now". Buffer timestamps can be used to 102 synchronize with other events.</para> 103 </refsect1> 104 105 <refsect1> 106 &return-value; 107 108 <variablelist> 109 <varlistentry> 110 <term><errorcode>EINVAL</errorcode></term> 111 <listitem> 112 <para>The buffer <structfield>type</structfield> is not supported, 113 or no buffers have been allocated (memory mapping) or enqueued 114 (output) yet.</para> 115 </listitem> 116 </varlistentry> 117 <varlistentry> 118 <term><errorcode>EPIPE</errorcode></term> 119 <listitem> 120 <para>The driver implements <link 121 linkend="pad-level-formats">pad-level format configuration</link> and 122 the pipeline configuration is invalid. 123 </para> 124 </listitem> 125 </varlistentry> 126 <varlistentry> 127 <term><errorcode>ENOLINK</errorcode></term> 128 <listitem> 129 <para>The driver implements Media Controller interface and 130 the pipeline link configuration is invalid. 131 </para> 132 </listitem> 133 </varlistentry> 134 </variablelist> 135 </refsect1> 136 </refentry>
