Re: [v4l-dvb-maintainer] bttv driver questions

[Trent Piepho <xyzzy@xxxxxxxxxxxxx>]

On Tue, 26 Aug 2008, Robert William Fuller wrote:
> Trent Piepho wrote:
> >> The driver fills buffers with instructions for the DMA engine, one buffer
> >> for the top field and one for the bottom field. These instructions tell
> >> the engine where to write a specific pixel. For interlaced video the
> >> instructions for the top field write to line 0, 2, 4, ... in memory and for
> >> the bottom field to line 1, 3, 5, ... .
> >
> > Keep in mind that _either_ field can be transmitted first.  I.e., in some
> > cases one first writes lines 1,3,5 then lines 0,2,4.  I'm not sure if bttv
> > supports both field dominances or not, but I think it does.
>
> My particular board always returns top field first on capture.  I don't
> know if that helps.

V4L2 allows the application to select the field dominance,
V4L2_FIELD_INTERLACED_TB vs V4L2_FIELD_INTERLACED_BT.  The bt878 chip can
support both, but I don't know if the bttv driver has support for it.

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