On 02/21/2014 12:30 AM, Laurent Pinchart wrote: > Hi Hans, > > On Thursday 20 February 2014 21:36:51 Hans Verkuil wrote: >> On 02/20/2014 08:41 PM, Sakari Ailus wrote: >>> Some devices do not produce timestamps that correspond to the end of the >>> frame. The user space should be informed on the matter. This patch >>> achieves >>> that by adding buffer flags (and a mask) for timestamp sources since more >>> possible timestamping points are expected than just two. >>> >>> A three-bit mask is defined (V4L2_BUF_FLAG_TSTAMP_SRC_MASK) and two of the >>> eight possible values is are defined V4L2_BUF_FLAG_TSTAMP_SRC_EOF for end >>> of frame (value zero) V4L2_BUF_FLAG_TSTAMP_SRC_SOE for start of exposure >>> (next value). >> >> Sorry, but I still have two small notes: >>> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxx> >>> --- >>> since v5: >>> - Add a note on software generated timestamp inaccuracy. >>> >>> Documentation/DocBook/media/v4l/io.xml | 38 +++++++++++++++++++++---- >>> drivers/media/v4l2-core/videobuf2-core.c | 4 +++- >>> include/media/videobuf2-core.h | 2 ++ >>> include/uapi/linux/videodev2.h | 4 ++++ >>> 4 files changed, 41 insertions(+), 7 deletions(-) >>> >>> diff --git a/Documentation/DocBook/media/v4l/io.xml >>> b/Documentation/DocBook/media/v4l/io.xml index 46d24b3..22b87bc 100644 >>> --- a/Documentation/DocBook/media/v4l/io.xml >>> +++ b/Documentation/DocBook/media/v4l/io.xml >>> @@ -653,12 +653,6 @@ plane, are stored in struct >>> <structname>v4l2_plane</structname> instead.> >>> In that case, struct <structname>v4l2_buffer</structname> contains an >>> array of plane structures.</para> >>> >>> - <para>For timestamp types that are sampled from the system clock >>> -(V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC) it is guaranteed that the timestamp >>> is >>> -taken after the complete frame has been received (or transmitted in >>> -case of video output devices). For other kinds of >>> -timestamps this may vary depending on the driver.</para> >>> - >>> >>> <table frame="none" pgwide="1" id="v4l2-buffer"> >>> >>> <title>struct <structname>v4l2_buffer</structname></title> >>> <tgroup cols="4"> >>> >>> @@ -1119,6 +1113,38 @@ in which case caches have not been used.</entry> >>> <entry>The CAPTURE buffer timestamp has been taken from the >>> corresponding OUTPUT buffer. This flag applies only to mem2mem >>> devices.</entry> >>> </row> >>> + <row> >>> + <entry><constant>V4L2_BUF_FLAG_TSTAMP_SRC_MASK</constant></entry> >>> + <entry>0x00070000</entry> >>> + <entry>Mask for timestamp sources below. The timestamp source >>> + defines the point of time the timestamp is taken in relation to >>> + the frame. Logical and operation between the >>> + <structfield>flags</structfield> field and >>> + <constant>V4L2_BUF_FLAG_TSTAMP_SRC_MASK</constant> produces the >>> + value of the timestamp source.</entry> >>> + </row> >>> + <row> >>> + <entry><constant>V4L2_BUF_FLAG_TSTAMP_SRC_EOF</constant></entry> >>> + <entry>0x00000000</entry> >>> + <entry>End Of Frame. The buffer timestamp has been taken >>> + when the last pixel of the frame has been received or the >>> + last pixel of the frame has been transmitted. In practice, >>> + software generated timestamps will typically be read from >>> + the clock a small amount of time after the last pixel has >>> + been received, depending on the system and other activity >> >> s/been received/been received or transmitted/ >> >>> + in it.</entry> >>> + </row> >>> + <row> >>> + <entry><constant>V4L2_BUF_FLAG_TSTAMP_SRC_SOE</constant></entry> >>> + <entry>0x00010000</entry> >>> + <entry>Start Of Exposure. The buffer timestamp has been >>> + taken when the exposure of the frame has begun. In >>> + practice, software generated timestamps will typically be >>> + read from the clock a small amount of time after the last >>> + pixel has been received, depending on the system and other >>> + activity in it. This is only valid for buffer type >>> + <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>.</entry> >> >> I would move the last sentence up to just before "In practice...". The >> way it is now it looks like an afterthought. >> >> I am also not sure whether the whole "In practice" sentence is valid >> here. Certainly the bit about "the last pixel" isn't since this is the >> "SOE" case and not the End Of Frame. In the case of the UVC driver (and >> that's the only one using this timestamp source) the timestamps come from >> the hardware as I understand it, so the "software generated" bit doesn't >> apply. >> >> I would actually be inclined to drop it altogether for this particular >> timestamp source. But it's up to Laurent. > > What do you mean, drop what altogether ? The "In practice ... activity in it." sentence. Regards, Hans > >>> + </row> >>> </tbody> >>> </tgroup> >>> </table> > -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
