aboutsummaryrefslogtreecommitdiff
path: root/Documentation/DocBook/media/v4l/io.xml
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/DocBook/media/v4l/io.xml')
-rw-r--r--Documentation/DocBook/media/v4l/io.xml53
1 files changed, 42 insertions, 11 deletions
diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml
index 388a3403265..09e8dcf5e9c 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>