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author | Sakari Ailus <sakari.ailus@iki.fi> | 2012-10-21 16:02:47 -0300 |
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committer | Mauro Carvalho Chehab <mchehab@redhat.com> | 2012-12-21 10:44:52 -0200 |
commit | 1202ecdc24fc88d5b144824f55ec9c8899591caf (patch) | |
tree | 97a4925b3ba400fbcd20b72ea81818a3bf62688f /Documentation/DocBook/media/v4l/io.xml | |
parent | 1b5901331ff3af4bdc1b998a056a248c9924e2d1 (diff) | |
download | op-kernel-dev-1202ecdc24fc88d5b144824f55ec9c8899591caf.zip op-kernel-dev-1202ecdc24fc88d5b144824f55ec9c8899591caf.tar.gz |
[media] v4l: Define video buffer flags for timestamp types
Define video buffer flags for different timestamp types. Everything up to
now have used either realtime clock or monotonic clock, without a way to
tell which clock the timestamp was taken from.
Also document that the clock source of the timestamp in the timestamp field
depends on buffer flags.
[mchehab@redhat.com: fix a few wrong references to Kernel 3.8 - as this patch
is meant for 3.9]
Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Diffstat (limited to 'Documentation/DocBook/media/v4l/io.xml')
-rw-r--r-- | Documentation/DocBook/media/v4l/io.xml | 53 |
1 files changed, 42 insertions, 11 deletions
diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml index 388a340..09e8dcf5 100644 --- a/Documentation/DocBook/media/v4l/io.xml +++ b/Documentation/DocBook/media/v4l/io.xml @@ -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> @@ -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> |