Markus Heiser | 5377d91 | 2016-06-30 15:18:56 +0200 | [diff] [blame^] | 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 | .. ------------------------------------------------------------------------------ |