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1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_STREAMON: |
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4 | |
5 | *************************************** | |
6 | ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF | |
7 | *************************************** | |
8 | ||
15e7d615 | 9 | Name |
586027ce | 10 | ==== |
5377d91f | 11 | |
586027ce | 12 | VIDIOC_STREAMON - VIDIOC_STREAMOFF - Start or stop streaming I/O |
5377d91f | 13 | |
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14 | |
15 | Synopsis | |
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16 | ======== |
17 | ||
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18 | .. c:function:: int ioctl( int fd, VIDIOC_STREAMON, const int *argp ) |
19 | :name: VIDIOC_STREAMON | |
20 | ||
21 | .. c:function:: int ioctl( int fd, VIDIOC_STREAMOFF, const int *argp ) | |
22 | :name: VIDIOC_STREAMOFF | |
5377d91f | 23 | |
586027ce | 24 | |
15e7d615 | 25 | Arguments |
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26 | ========= |
27 | ||
28 | ``fd`` | |
29 | File descriptor returned by :ref:`open() <func-open>`. | |
30 | ||
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31 | ``argp`` |
32 | ||
33 | ||
15e7d615 | 34 | Description |
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35 | =========== |
36 | ||
37 | The ``VIDIOC_STREAMON`` and ``VIDIOC_STREAMOFF`` ioctl start and stop | |
38 | the capture or output process during streaming | |
39 | (:ref:`memory mapping <mmap>`, :ref:`user pointer <userp>` or | |
40 | :ref:`DMABUF <dmabuf>`) I/O. | |
41 | ||
42 | Capture hardware is disabled and no input buffers are filled (if there | |
43 | are any empty buffers in the incoming queue) until ``VIDIOC_STREAMON`` | |
44 | has been called. Output hardware is disabled and no video signal is | |
45 | produced until ``VIDIOC_STREAMON`` has been called. The ioctl will | |
46 | succeed when at least one output buffer is in the incoming queue. | |
47 | ||
48 | Memory-to-memory devices will not start until ``VIDIOC_STREAMON`` has | |
49 | been called for both the capture and output stream types. | |
50 | ||
51 | If ``VIDIOC_STREAMON`` fails then any already queued buffers will remain | |
52 | queued. | |
53 | ||
54 | The ``VIDIOC_STREAMOFF`` ioctl, apart of aborting or finishing any DMA | |
55 | in progress, unlocks any user pointer buffers locked in physical memory, | |
56 | and it removes all buffers from the incoming and outgoing queues. That | |
57 | means all images captured but not dequeued yet will be lost, likewise | |
58 | all images enqueued for output but not transmitted yet. I/O returns to | |
59 | the same state as after calling | |
7347081e | 60 | :ref:`VIDIOC_REQBUFS` and can be restarted |
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61 | accordingly. |
62 | ||
7347081e | 63 | If buffers have been queued with :ref:`VIDIOC_QBUF` and |
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64 | ``VIDIOC_STREAMOFF`` is called without ever having called |
65 | ``VIDIOC_STREAMON``, then those queued buffers will also be removed from | |
66 | the incoming queue and all are returned to the same state as after | |
7347081e | 67 | calling :ref:`VIDIOC_REQBUFS` and can be restarted |
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68 | accordingly. |
69 | ||
70 | Both ioctls take a pointer to an integer, the desired buffer or stream | |
71 | type. This is the same as struct | |
e8be7e97 | 72 | :c:type:`v4l2_requestbuffers` ``type``. |
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73 | |
74 | If ``VIDIOC_STREAMON`` is called when streaming is already in progress, | |
75 | or if ``VIDIOC_STREAMOFF`` is called when streaming is already stopped, | |
76 | then 0 is returned. Nothing happens in the case of ``VIDIOC_STREAMON``, | |
77 | but ``VIDIOC_STREAMOFF`` will return queued buffers to their starting | |
78 | state as mentioned above. | |
79 | ||
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80 | .. note:: |
81 | ||
82 | Applications can be preempted for unknown periods right before | |
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83 | or after the ``VIDIOC_STREAMON`` or ``VIDIOC_STREAMOFF`` calls, there is |
84 | no notion of starting or stopping "now". Buffer timestamps can be used | |
85 | to synchronize with other events. | |
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86 | |
87 | ||
15e7d615 | 88 | Return Value |
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89 | ============ |
90 | ||
91 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
92 | appropriately. The generic error codes are described at the | |
93 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
94 | ||
95 | EINVAL | |
96 | The buffer ``type`` is not supported, or no buffers have been | |
97 | allocated (memory mapping) or enqueued (output) yet. | |
98 | ||
99 | EPIPE | |
100 | The driver implements | |
101 | :ref:`pad-level format configuration <pad-level-formats>` and the | |
102 | pipeline configuration is invalid. | |
103 | ||
104 | ENOLINK | |
105 | The driver implements Media Controller interface and the pipeline | |
106 | link configuration is invalid. |