By Date: <-- -->
By Thread: <-- -->

bttv 2.6.16: wrong VBI_OFFSET?

Trent Piepho wrote:
>
> On Wed, 3 May 2006, Edgar Toernig wrote:
> > | Hmm... played around with this.  It seems, the real offset is dependent
> > | on hscale.  Samples start earlier/later when capture window is resized.
> > | Strange...  Good luck you driver writers ;)
> > |...
> > | Btw, (186-64)*2 = 244  (186 = recommended hdelay for PAL).
> 
> I did some more tests with different parameters:
> http://www.speakeasy.org/~xyzzy/vbi
> 
> According to my tests, changing HSCALE, HDELAY, and BGDELAY have no effect on
> vbi start offset.  It always appears to start about 220 pixels at Clk*2 from
> 0H.  Changing HSFMT has the expected effect for the bt878, but doesn't appear
> to have any effect on the cx23880, unless something extra must be done for a
> change in HSFMT to take effect.  Changing VBI_HDELAY has the expected effect.
> 
> For NTSC, the burst gate delay is set to 93 Clk*2 pixels.  /HRESET width is
> 128 Clk*2 pixels.  93+128 = 221, observed value of vbi delay.  But changing
> bgdel has no effect.. oh well.

FWIW, PAL's burst delay is 117, 128+117 = 242 - not bad either.  If changing
bdelay had shown an effect I would have said "that's it" :-(  It's wicked.

Concerning Daniel's diagram, it looks nice but I have some doubts whether
his calculations are 100% correct - it looks too strange especially the
completely different pattern when HSFMT is changed.  Daniel, as you calculate
the offset 'backwards' (samples to next 0H), is it possible that you have
a math bug with the scaling of the rest of the line? 

Btw, the hscale effect I mentioned in my old posting was observed with a Bt878
Rev 2.  It seems that's a pretty old revision as my current DVB card has a
Bt878 Rev 11 (at least 9 bugs less *g*).  I cannot remember how strong the
effect was - I think it was not as big as Daniel's diagram would suggest.

Well, the easy fix for this mess is to simply use 244 for PAL and 220 for
NTSC and wait till somebody complains ;-)  Heck, better than Windows - it
seems those guys have to edit the registry and set VBI_HDELAY by hand: 7 for
NTSC and 25 for PAL.  Oh, I just read in Typhoon's FAQ that CC does not work
when the video window is smaller than 240 pixels ...

Ciao, ET.

--
video4linux-list mailing list
Unsubscribe mailto:video4linux-list-request (at) redhat.com?subject=unsubscribe
https://www.redhat.com/mailman/listinfo/video4linux-list