| 1 | .. -*- coding: utf-8; mode: rst -*- |
| 2 | |
| 3 | .. _VIDIOC_STREAMON: |
| 4 | |
| 5 | *************************************** |
| 6 | ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF |
| 7 | *************************************** |
| 8 | |
| 9 | Name |
| 10 | ==== |
| 11 | |
| 12 | VIDIOC_STREAMON - VIDIOC_STREAMOFF - Start or stop streaming I/O |
| 13 | |
| 14 | |
| 15 | Synopsis |
| 16 | ======== |
| 17 | |
| 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 |
| 23 | |
| 24 | |
| 25 | Arguments |
| 26 | ========= |
| 27 | |
| 28 | ``fd`` |
| 29 | File descriptor returned by :ref:`open() <func-open>`. |
| 30 | |
| 31 | ``argp`` |
| 32 | |
| 33 | |
| 34 | Description |
| 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 |
| 60 | :ref:`VIDIOC_REQBUFS` and can be restarted |
| 61 | accordingly. |
| 62 | |
| 63 | If buffers have been queued with :ref:`VIDIOC_QBUF` and |
| 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 |
| 67 | calling :ref:`VIDIOC_REQBUFS` and can be restarted |
| 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 |
| 72 | :c:type:`v4l2_requestbuffers` ``type``. |
| 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 | |
| 80 | .. note:: |
| 81 | |
| 82 | Applications can be preempted for unknown periods right before |
| 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. |
| 86 | |
| 87 | |
| 88 | Return Value |
| 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. |