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RF connectors and v4l2

On Monday 27 February 2006 12:59 pm, Jon M. Lamb wrote:
> Hello to all,
>
> I posted this in a thread and got no response but it may
> not have been the proper place to ask.  Anyway....
>
> 	Michael Krufky wrote:
>
>
>     Please see the discussion in the list between Mac
> Michaels, Kirk Lapray and I about this very topic. We
> agree     with you, but the API doesnt allow it in analog
> mode, unless you can change tuner input using GPIO...
>
>
> I was reading the Video for Linux Two API Specifications
> (Is this the API referred to) trying to understand them.
> Under section 1.6.1 Tuners of the specification it says:
>
>     Video input devices can have one or more tuners
> demodulating a RF signal. Each tuner is associated with
> one or more video inputs, depending on the number of RF
> connectors on the tuner.
>
>
> And in section 6.2.9 V4L2 in Linux 2.5.46 2002-10 it
> says:
>
>     6. The struct v4l2_tuner
> <http://v4l2spec.bytesex.org/spec-single/v4l2.html#V4L2-T
>UNER> |input| field was replaced by an |index| field,
> permitting devices with multiple tuners. The link between
> video inputs and tuners is now reversed, inputs point to
> the tuner they are on. The |std| substructure became a
> simple set (more about this below) and moved into struct
> v4l2_input
> <http://v4l2spec.bytesex.org/spec-single/v4l2.html#V4L2-I
>NPUT>. A |type| field was added.
>
>
> To me this implies that the API spec does handle RF input
> selection by selecting a different video input. The
> driver should be able to define any number of inputs, RF
> or not, which could point to the same tuner. Am I
> misinterpreting the API Spec?
>
> Jon

This is how I interpreted the spec when I implemented the 
driver for DViCO HDTV3 Gold-Q. This is one of the few cards 
that uses a Tuner with two RF input connectors used for 
analog TV. Either RF connector can be used for over-the-air 
or cable. The actual frequency tuned is under control of 
the application.

This card also handles digital TV using the same tuner. It 
works a bit differently. For digital signals one connector 
is assigned to VSB-8 for over the air and the other 
connector is assigned to QAM-256 for cable. (The connectors 
are actually labeled ANT and CABLE although either RF 
connector can be selected for VSB-8 or QAM-256.) This was 
done because the DVB API has no way to select a video 
source ... it is digital data not video. Neither spec had 
an RF input selector.

-- Mac

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