107 lines
3.4 KiB
ReStructuredText
107 lines
3.4 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_STREAMON:
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***************************************
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ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF
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***************************************
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Name
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====
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VIDIOC_STREAMON - VIDIOC_STREAMOFF - Start or stop streaming I/O
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Synopsis
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========
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.. c:function:: int ioctl( int fd, VIDIOC_STREAMON, const int *argp )
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:name: VIDIOC_STREAMON
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.. c:function:: int ioctl( int fd, VIDIOC_STREAMOFF, const int *argp )
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:name: VIDIOC_STREAMOFF
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <func-open>`.
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``argp``
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Description
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===========
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The ``VIDIOC_STREAMON`` and ``VIDIOC_STREAMOFF`` ioctl start and stop
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the capture or output process during streaming
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(:ref:`memory mapping <mmap>`, :ref:`user pointer <userp>` or
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:ref:`DMABUF <dmabuf>`) I/O.
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Capture hardware is disabled and no input buffers are filled (if there
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are any empty buffers in the incoming queue) until ``VIDIOC_STREAMON``
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has been called. Output hardware is disabled and no video signal is
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produced until ``VIDIOC_STREAMON`` has been called. The ioctl will
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succeed when at least one output buffer is in the incoming queue.
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Memory-to-memory devices will not start until ``VIDIOC_STREAMON`` has
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been called for both the capture and output stream types.
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If ``VIDIOC_STREAMON`` fails then any already queued buffers will remain
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queued.
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The ``VIDIOC_STREAMOFF`` ioctl, apart of aborting or finishing any DMA
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in progress, unlocks any user pointer buffers locked in physical memory,
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and it removes all buffers from the incoming and outgoing queues. That
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means all images captured but not dequeued yet will be lost, likewise
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all images enqueued for output but not transmitted yet. I/O returns to
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the same state as after calling
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:ref:`VIDIOC_REQBUFS` and can be restarted
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accordingly.
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If buffers have been queued with :ref:`VIDIOC_QBUF` and
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``VIDIOC_STREAMOFF`` is called without ever having called
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``VIDIOC_STREAMON``, then those queued buffers will also be removed from
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the incoming queue and all are returned to the same state as after
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calling :ref:`VIDIOC_REQBUFS` and can be restarted
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accordingly.
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Both ioctls take a pointer to an integer, the desired buffer or stream
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type. This is the same as struct
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:c:type:`v4l2_requestbuffers` ``type``.
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If ``VIDIOC_STREAMON`` is called when streaming is already in progress,
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or if ``VIDIOC_STREAMOFF`` is called when streaming is already stopped,
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then 0 is returned. Nothing happens in the case of ``VIDIOC_STREAMON``,
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but ``VIDIOC_STREAMOFF`` will return queued buffers to their starting
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state as mentioned above.
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.. note::
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Applications can be preempted for unknown periods right before
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or after the ``VIDIOC_STREAMON`` or ``VIDIOC_STREAMOFF`` calls, there is
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no notion of starting or stopping "now". Buffer timestamps can be used
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to synchronize with other events.
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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EINVAL
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The buffer ``type`` is not supported, or no buffers have been
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allocated (memory mapping) or enqueued (output) yet.
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EPIPE
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The driver implements
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:ref:`pad-level format configuration <pad-level-formats>` and the
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pipeline configuration is invalid.
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ENOLINK
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The driver implements Media Controller interface and the pipeline
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link configuration is invalid.
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