Re: [PATCH 1/2] [media] V4L: Add camera pan/tilt speed controls

Vincent Palatin
2014-08-08T16:41:21Z

On Wed, Aug 6, 2014 at 7:18 PM, Pawel Osciak <posciak@chromium.org> wrote:
>
> On Thu, Aug 7, 2014 at 12:10 AM, Vincent Palatin <vpalatin@chromium.org> wrote:
> >
> > On Sun, Aug 3, 2014 at 10:52 PM, Pawel Osciak <posciak@chromium.org> wrote:
> > > This looks good to me in general (with one comment below). I don't think we
> > > can easily implement current V4L2 pan and tilt controls that are for
> > > movement by a specified amount in terms of UVC pan/tilt speed controls,
> > > which only let us set speed and direction...
> > >
> > > On Wed, Jul 9, 2014 at 8:49 AM, Vincent Palatin <vpalatin@chromium.org>
> > > wrote:
> > >>
> > >> The V4L2_CID_PAN_SPEED and V4L2_CID_TILT_SPEED controls allow to move the
> > >> camera by setting its rotation speed around its axis.
> > >>
> > >> Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
> > >>
> > >> ---
> > >> Documentation/DocBook/media/v4l/compat.xml | 10 ++++++++++
> > >> Documentation/DocBook/media/v4l/controls.xml | 21 +++++++++++++++++++++
> > >> drivers/media/v4l2-core/v4l2-ctrls.c | 2 ++
> > >> include/uapi/linux/v4l2-controls.h | 2 ++
> > >> 4 files changed, 35 insertions(+)
> > >>
> > >> diff --git a/Documentation/DocBook/media/v4l/compat.xml
> > >> b/Documentation/DocBook/media/v4l/compat.xml
> > >> index eee6f0f..21910e9 100644
> > >> --- a/Documentation/DocBook/media/v4l/compat.xml
> > >> +++ b/Documentation/DocBook/media/v4l/compat.xml
> > >> @@ -2545,6 +2545,16 @@ fields changed from _s32 to _u32.
> > >>
> > >>
> > >>
> > >> +
> > >> + V4L2 in Linux 3.17
> > >> +
> > >> +
> > >> + Added <constant>V4L2_CID_PAN_SPEED</constant> and
> > >> + <constant>V4L2_CID_TILT_SPEED</constant> camera controls.
> > >> +
> > >> +
> > >> +
> > >> +
> > >>
> > >> Relation of V4L2 to other Linux multimedia APIs
> > >>
> > >> diff --git a/Documentation/DocBook/media/v4l/controls.xml
> > >> b/Documentation/DocBook/media/v4l/controls.xml
> > >> index 47198ee..cdf97f0 100644
> > >> --- a/Documentation/DocBook/media/v4l/controls.xml
> > >> +++ b/Documentation/DocBook/media/v4l/controls.xml
> > >> @@ -3914,6 +3914,27 @@ by exposure, white balance or focus
> > >> controls.</entry>
> > >> </row>
> > >> <row><entry></entry></row>
> > >>
> > >> + <row>
> > >> + <entry
> > >> spanname="id"><constant>V4L2_CID_PAN_SPEED</constant>&nbsp;</entry>
> > >> + <entry>integer</entry>
> > >> + </row><row><entry spanname="descr">This control turns the
> > >> +camera horizontally at the specific speed. The unit is undefined. A
> > >> +positive value moves the camera to the right (clockwise when viewed
> > >> +from above), a negative value to the left. A value of zero does not
> > >> +cause or stop the motion.</entry>
> > >
> > >
> > > How do we stop/start?
> >
> > As mentioned in the last sentence of the paragraph above, setting 0
> > stops the movement.
> > setting non-zero value starts it if needed.
> >
>
> The sentence says "A value of zero does *not* cause or stop the
> motion.". Perhaps "not" is a typo then?

maybe my phrasing is really bad but the "not" isn't a typo.
The developed version would be :
"A value of zero does *not* cause [any motion if the camera is already stopped]
or stop the motion [if it is currently moving with a non-zero speed]"

--
Vincent