diff options
Diffstat (limited to 'Documentation/DocBook/media/v4l/io.xml')
| -rw-r--r-- | Documentation/DocBook/media/v4l/io.xml | 59 |
1 files changed, 45 insertions, 14 deletions
diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml index 388a34032653..e6c58559ca6b 100644 --- a/Documentation/DocBook/media/v4l/io.xml +++ b/Documentation/DocBook/media/v4l/io.xml @@ -477,7 +477,7 @@ rest should be evident.</para> <note> <title>Experimental</title> - <para>This is an <link linkend="experimental"> experimental </link> + <para>This is an <link linkend="experimental">experimental</link> interface and may change in the future.</para> </note> @@ -488,7 +488,7 @@ DMA buffer from userspace using a file descriptor previously exported for a different or the same device (known as the importer role), or both. This section describes the DMABUF importer role API in V4L2.</para> - <para>Refer to <link linked="vidioc-expbuf"> DMABUF exporting </link> for + <para>Refer to <link linkend="vidioc-expbuf">DMABUF exporting</link> for details about exporting V4L2 buffers as DMABUF file descriptors.</para> <para>Input and output devices support the streaming I/O method when the @@ -741,17 +741,19 @@ applications when an output stream.</entry> <entry>struct timeval</entry> <entry><structfield>timestamp</structfield></entry> <entry></entry> - <entry><para>For input streams this is the -system time (as returned by the <function>gettimeofday()</function> -function) when the first data byte was captured. For output streams -the data will not be displayed before this time, secondary to the -nominal frame rate determined by the current video standard in -enqueued order. Applications can for example zero this field to -display frames as soon as possible. The driver stores the time at -which the first data byte was actually sent out in the -<structfield>timestamp</structfield> field. This permits -applications to monitor the drift between the video and system -clock.</para></entry> + <entry><para>For input streams this is time when the first data + byte was captured, as returned by the + <function>clock_gettime()</function> function for the relevant + clock id; see <constant>V4L2_BUF_FLAG_TIMESTAMP_*</constant> in + <xref linkend="buffer-flags" />. For output streams the data + will not be displayed before this time, secondary to the nominal + frame rate determined by the current video standard in enqueued + order. Applications can for example zero this field to display + frames as soon as possible. The driver stores the time at which + the first data byte was actually sent out in the + <structfield>timestamp</structfield> field. This permits + applications to monitor the drift between the video and system + clock.</para></entry> </row> <row> <entry>&v4l2-timecode;</entry> @@ -903,7 +905,7 @@ should set this to 0.</entry> </row> <row> <entry></entry> - <entry>__unsigned long</entry> + <entry>unsigned long</entry> <entry><structfield>userptr</structfield></entry> <entry>When the memory type in the containing &v4l2-buffer; is <constant>V4L2_MEMORY_USERPTR</constant>, this is a userspace @@ -1114,6 +1116,35 @@ Typically applications shall use this flag for output buffers if the data in this buffer has not been created by the CPU but by some DMA-capable unit, in which case caches have not been used.</entry> </row> + <row> + <entry><constant>V4L2_BUF_FLAG_TIMESTAMP_MASK</constant></entry> + <entry>0xe000</entry> + <entry>Mask for timestamp types below. To test the + timestamp type, mask out bits not belonging to timestamp + type by performing a logical and operation with buffer + flags and timestamp mask.</entry> + </row> + <row> + <entry><constant>V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN</constant></entry> + <entry>0x0000</entry> + <entry>Unknown timestamp type. This type is used by + drivers before Linux 3.9 and may be either monotonic (see + below) or realtime (wall clock). Monotonic clock has been + favoured in embedded systems whereas most of the drivers + use the realtime clock. Either kinds of timestamps are + available in user space via + <function>clock_gettime(2)</function> using clock IDs + <constant>CLOCK_MONOTONIC</constant> and + <constant>CLOCK_REALTIME</constant>, respectively.</entry> + </row> + <row> + <entry><constant>V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC</constant></entry> + <entry>0x2000</entry> + <entry>The buffer timestamp has been taken from the + <constant>CLOCK_MONOTONIC</constant> clock. To access the + same clock outside V4L2, use + <function>clock_gettime(2)</function> .</entry> + </row> </tbody> </tgroup> </table> |
