Re: [Discuss-gnuradio] Hardware costs

[Hermann Gausterer]

On Fri, Mar 14, 2003 at 11:14:16PM -0700, Mike Turvey wrote:
> The VBI frame output mode looks
> good because it doesn't appear to depend on the HSYNC signal at all.

maybe .. maybe not .. this is hard to guess :-(

> The one sentence that really concerned me was: "VDELAY must also be set
> to its minimum value of 2."  What this sounds like to me is that two
> whole lines worth of video data get lost here.  For video, this is no
> problem because it's in the middle of the vertical sync signal, but it
> could pose quite a hole for us.  

if we are lucky (and i am a lucky boy in my life ;-) ; and it is realy a
coninues data capture (lets pray ;-) , it might be enough to only 
generate von VSYNC sequence with external logic and after this the
bt8X9 does what we want :-))

> If this is a hole as it appears to be, and there's no way around it, one
> possible option would be to use two cards in a computer and feed them
> different sync signals so their "holes" don't overlap, then merge the
> samples from each in software (could be messy).

in such a construct, and in case the assumtations above are false,
we should also interlive the horizontal lines, so we could add the
normal hsync pulses and because they are from the same generatorlogik
on both cards we could use the voltage level of the sync for 
permanent recalibration of the two channels :-))
the program has to read the always from the right card in
every moment (there where no sync is ;-) and compare
the voltage values ...

of course only if the A/D`s are near to linear ;-)

     -----------------
     | h/v sync gen. | (the two outputs are normal FBAS)
     ----------------- (with a halfe line + a halfe frame = 1/4 picture) 
        |1       |2    (phase difference)
IN      V        |      -------- 
------>|+|------------->|BTTV 1|
   |             V      --------
   ------------>|+|---->|BTTV 1|
                        --------

this should "just work" (TM) :-))

hermann