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@@ -52,16 +52,24 @@
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<para>The <constant>VIDIOC_STREAMON</constant> and
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<constant>VIDIOC_STREAMOFF</constant> ioctl start and stop the capture
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or output process during streaming (<link linkend="mmap">memory
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-mapping</link> or <link linkend="userp">user pointer</link>) I/O.</para>
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+mapping</link>, <link linkend="userp">user pointer</link> or
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+<link linkend="dmabuf">DMABUF</link>) I/O.</para>
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- <para>Specifically the capture hardware is disabled and no input
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+ <para>Capture hardware is disabled and no input
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buffers are filled (if there are any empty buffers in the incoming
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queue) until <constant>VIDIOC_STREAMON</constant> has been called.
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-Accordingly the output hardware is disabled, no video signal is
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+Output hardware is disabled and no video signal is
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produced until <constant>VIDIOC_STREAMON</constant> has been called.
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The ioctl will succeed when at least one output buffer is in the
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incoming queue.</para>
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+ <para>Memory-to-memory devices will not start until
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+<constant>VIDIOC_STREAMON</constant> has been called for both the capture
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+and output stream types.</para>
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+
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+ <para>If <constant>VIDIOC_STREAMON</constant> fails then any already
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+queued buffers will remain queued.</para>
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+
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<para>The <constant>VIDIOC_STREAMOFF</constant> ioctl, apart of
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aborting or finishing any DMA in progress, unlocks any user pointer
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buffers locked in physical memory, and it removes all buffers from the
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@@ -70,14 +78,22 @@ dequeued yet will be lost, likewise all images enqueued for output but
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not transmitted yet. I/O returns to the same state as after calling
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&VIDIOC-REQBUFS; and can be restarted accordingly.</para>
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+ <para>If buffers have been queued with &VIDIOC-QBUF; and
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+<constant>VIDIOC_STREAMOFF</constant> is called without ever having
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+called <constant>VIDIOC_STREAMON</constant>, then those queued buffers
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+will also be removed from the incoming queue and all are returned to the
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+same state as after calling &VIDIOC-REQBUFS; and can be restarted
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+accordingly.</para>
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+
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<para>Both ioctls take a pointer to an integer, the desired buffer or
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stream type. This is the same as &v4l2-requestbuffers;
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<structfield>type</structfield>.</para>
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<para>If <constant>VIDIOC_STREAMON</constant> is called when streaming
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is already in progress, or if <constant>VIDIOC_STREAMOFF</constant> is called
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-when streaming is already stopped, then the ioctl does nothing and 0 is
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-returned.</para>
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+when streaming is already stopped, then 0 is returned. Nothing happens in the
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+case of <constant>VIDIOC_STREAMON</constant>, but <constant>VIDIOC_STREAMOFF</constant>
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+will return queued buffers to their starting state as mentioned above.</para>
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<para>Note that applications can be preempted for unknown periods right
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before or after the <constant>VIDIOC_STREAMON</constant> or
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@@ -93,7 +109,7 @@ synchronize with other events.</para>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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- <para>The buffer<structfield>type</structfield> is not supported,
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+ <para>The buffer <structfield>type</structfield> is not supported,
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or no buffers have been allocated (memory mapping) or enqueued
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(output) yet.</para>
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</listitem>
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Hans Verkuil