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1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
3 | .. _vidioc-streamon: | |
4 | ||
5 | *************************************** | |
6 | ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF | |
7 | *************************************** | |
8 | ||
9 | *man VIDIOC_STREAMON(2)* | |
10 | ||
11 | VIDIOC_STREAMOFF | |
12 | Start or stop streaming I/O | |
13 | ||
14 | ||
15 | Synopsis | |
16 | ======== | |
17 | ||
18 | .. c:function:: int ioctl( int fd, int request, const int *argp ) | |
19 | ||
20 | Arguments | |
21 | ========= | |
22 | ||
23 | ``fd`` | |
24 | File descriptor returned by :ref:`open() <func-open>`. | |
25 | ||
26 | ``request`` | |
27 | VIDIOC_STREAMON, VIDIOC_STREAMOFF | |
28 | ||
29 | ``argp`` | |
30 | ||
31 | ||
32 | Description | |
33 | =========== | |
34 | ||
35 | The ``VIDIOC_STREAMON`` and ``VIDIOC_STREAMOFF`` ioctl start and stop | |
36 | the capture or output process during streaming | |
37 | (:ref:`memory mapping <mmap>`, :ref:`user pointer <userp>` or | |
38 | :ref:`DMABUF <dmabuf>`) I/O. | |
39 | ||
40 | Capture hardware is disabled and no input buffers are filled (if there | |
41 | are any empty buffers in the incoming queue) until ``VIDIOC_STREAMON`` | |
42 | has been called. Output hardware is disabled and no video signal is | |
43 | produced until ``VIDIOC_STREAMON`` has been called. The ioctl will | |
44 | succeed when at least one output buffer is in the incoming queue. | |
45 | ||
46 | Memory-to-memory devices will not start until ``VIDIOC_STREAMON`` has | |
47 | been called for both the capture and output stream types. | |
48 | ||
49 | If ``VIDIOC_STREAMON`` fails then any already queued buffers will remain | |
50 | queued. | |
51 | ||
52 | The ``VIDIOC_STREAMOFF`` ioctl, apart of aborting or finishing any DMA | |
53 | in progress, unlocks any user pointer buffers locked in physical memory, | |
54 | and it removes all buffers from the incoming and outgoing queues. That | |
55 | means all images captured but not dequeued yet will be lost, likewise | |
56 | all images enqueued for output but not transmitted yet. I/O returns to | |
57 | the same state as after calling | |
58 | :ref:`VIDIOC_REQBUFS <vidioc-reqbufs>` and can be restarted | |
59 | accordingly. | |
60 | ||
61 | If buffers have been queued with :ref:`VIDIOC_QBUF <vidioc-qbuf>` and | |
62 | ``VIDIOC_STREAMOFF`` is called without ever having called | |
63 | ``VIDIOC_STREAMON``, then those queued buffers will also be removed from | |
64 | the incoming queue and all are returned to the same state as after | |
65 | calling :ref:`VIDIOC_REQBUFS <vidioc-reqbufs>` and can be restarted | |
66 | accordingly. | |
67 | ||
68 | Both ioctls take a pointer to an integer, the desired buffer or stream | |
69 | type. This is the same as struct | |
70 | :ref:`v4l2_requestbuffers <v4l2-requestbuffers>` ``type``. | |
71 | ||
72 | If ``VIDIOC_STREAMON`` is called when streaming is already in progress, | |
73 | or if ``VIDIOC_STREAMOFF`` is called when streaming is already stopped, | |
74 | then 0 is returned. Nothing happens in the case of ``VIDIOC_STREAMON``, | |
75 | but ``VIDIOC_STREAMOFF`` will return queued buffers to their starting | |
76 | state as mentioned above. | |
77 | ||
78 | Note that applications can be preempted for unknown periods right before | |
79 | or after the ``VIDIOC_STREAMON`` or ``VIDIOC_STREAMOFF`` calls, there is | |
80 | no notion of starting or stopping "now". Buffer timestamps can be used | |
81 | to synchronize with other events. | |
82 | ||
83 | ||
84 | Return Value | |
85 | ============ | |
86 | ||
87 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
88 | appropriately. The generic error codes are described at the | |
89 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
90 | ||
91 | EINVAL | |
92 | The buffer ``type`` is not supported, or no buffers have been | |
93 | allocated (memory mapping) or enqueued (output) yet. | |
94 | ||
95 | EPIPE | |
96 | The driver implements | |
97 | :ref:`pad-level format configuration <pad-level-formats>` and the | |
98 | pipeline configuration is invalid. | |
99 | ||
100 | ENOLINK | |
101 | The driver implements Media Controller interface and the pipeline | |
102 | link configuration is invalid. | |
103 | ||
104 | ||
105 | .. ------------------------------------------------------------------------------ | |
106 | .. This file was automatically converted from DocBook-XML with the dbxml | |
107 | .. library (https://github.com/return42/sphkerneldoc). The origin XML comes | |
108 | .. from the linux kernel, refer to: | |
109 | .. | |
110 | .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook | |
111 | .. ------------------------------------------------------------------------------ |