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8e080c2e MCC |
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> or <link linkend="userp">user pointer</link>) I/O.</para> | |
56 | ||
57 | <para>Specifically the capture hardware is disabled and no input | |
58 | buffers are filled (if there are any empty buffers in the incoming | |
59 | queue) until <constant>VIDIOC_STREAMON</constant> has been called. | |
60 | Accordingly the output hardware is disabled, no video signal is | |
61 | produced until <constant>VIDIOC_STREAMON</constant> has been called. | |
62 | The ioctl will succeed only when at least one output buffer is in the | |
63 | incoming queue.</para> | |
64 | ||
65 | <para>The <constant>VIDIOC_STREAMOFF</constant> ioctl, apart of | |
66 | aborting or finishing any DMA in progress, unlocks any user pointer | |
67 | buffers locked in physical memory, and it removes all buffers from the | |
68 | incoming and outgoing queues. That means all images captured but not | |
69 | dequeued yet will be lost, likewise all images enqueued for output but | |
70 | not 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 | |
74 | stream 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 | |
78 | before or after the <constant>VIDIOC_STREAMON</constant> or | |
79 | <constant>VIDIOC_STREAMOFF</constant> calls, there is no notion of | |
80 | starting or stopping "now". Buffer timestamps can be used to | |
81 | synchronize 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 | |
93 | been allocated (memory mapping) or enqueued (output) yet.</para> | |
94 | </listitem> | |
95 | </varlistentry> | |
96 | </variablelist> | |
97 | </refsect1> | |
98 | </refentry> | |
99 | ||
100 | <!-- | |
101 | Local Variables: | |
102 | mode: sgml | |
103 | sgml-parent-document: "v4l2.sgml" | |
104 | indent-tabs-mode: nil | |
105 | End: | |
106 | --> |