On Thursday, September 09, 2010 08:07:02 Jean-Francois Moine wrote:
> On Wed, 08 Sep 2010 20:58:18 +0200
> Peter Korsgaard <jac...@sunsite.dk> wrote:
> > >>>>> "Andy" == Andy Walls <awa...@md.metrocast.net> writes:
> > Andy> Incandescent and Halogen lamps that effect an image coming
> > Andy> into a camera are *not* LEDs that blink or flash automatically
> > Andy> based on driver or system trigger events. They are components
> > Andy> of a video capture system with which a human attempts to
> > Andy> adjust the appearance of an image of a subject by changing the
> > Andy> subject's environment. These illuminators are not some
> > Andy> generically connected device, but controlled by GPIO's on the
> > Andy> camera's bridge or sensor chip itself. Such an illuminator
> > Andy> will essentially be used only in conjunction with the camera.
> >
> > Agreed.
> >
> > Andy> Status LEDs integrated into webcam devices that are not
> > Andy> generically connected devices but controlled with GPIOs on the
> > Andy> camera's bridge or sensor chip will also essentially be used
> > Andy> only in conjunction with the camera.
> >
> > Or for any other usage the user envision - E.G. I could imagine using
> > the status led of the webcam in my macbook for hard disk or wifi
> > activity. I'm sure other people can come up with more creative use
> > cases as well.
> >
> > Andy> Turning these sorts camera specific illuminators and LEDs on
> > Andy> an off should be as simple to implement for an application
> > Andy> developer as it is to grasp the concept of turning a light
> > Andy> bulb on and off.
> >
> > The point is that the logic rarely needs to be in the v4l
> > applications. The status LEDs should by default go on when the v4l
> > device is active and go off again when not like it used to do. A v4l
> > application developer would normally not want to worry about such
> > things, and only care about the video data.
> >
> > But if a user wants something special / non-standard, then it's just a
> > matter of changing LED trigger in /sys/class/leds/..
> [snip]
> > Again, for status LEDs I don't see any reason why a standard v4l tool
> > would care. As I mentioned above, illuminators are a different story
> > (comparable to a gain setting imho).
> [snip]
> > Again, I see the sysfs LED interface for status LEDs as more of a
> > user/administrator interface than a programming API.
>
> Hi,
>
> If I may resume this exchange:
>
> - the (microscope or device dependant) illuminators may be controlled
> by v4l2,
Agreed.
> - the status LED should be controlled by the LED interface.
I originally was in favor of controlling these through v4l as well, but people
made some good arguments against that. The main one being: why would you want
to show these as a control? What is the end user supposed to do with them? It
makes little sense.
Frankly, why would you want to expose LEDs at all? Shouldn't this be completely
hidden by the driver? No generic application will ever do anything with status
LEDs anyway. So it should be the driver that operates them and in that case the
LEDs do not need to be exposed anywhere.
In some embedded systems there may be a need to actually expose the LEDs, and in
that case the standard LED API can be used. And the upcoming media API can, if
necessary, be used to let the app know where to find the LED device associated
with the video hardware.
Regards,
Hans
--
Hans Verkuil - video4linux developer - sponsored by TANDBERG, part of Cisco
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