[Openchrome-users] PAL modes and vx800

[Anders Gunnarsson]

fredag 06 februari 2009 10:09:38 skrev Paul Gardiner:
> Anders Gunnarsson wrote:
> > On Thursday 05 February 2009 11:37:42 Tim Williams wrote:
> >> On Wed, 4 Feb 2009, Anders Gunnarsson wrote:
> >>> As I understand you need support for a slow rate on the dot clock,
> >>> around 14MHz. Both open chrome and the via drivers give me "Clock
> >>> range:  20.00 to 230.00 MHz". Does that mean I'm smoked?
> >>
> >> As an experiment I built a convertor circuit (using the
> >> design on http://www.nexusuk.org/projects/vga2scart) a year or two
> >> ago. Cost very little and it works beautifully, I built it small enough
> >> to fit inside a standard plastic scart plug. However my experiments
> >> proved that you need a dot clock of ~14Mhz to get it to work. Haven't
> >> tried it with an OpenChrome driver, it worked with the Nvidia card on my
> >> regular desktop, but failed with the intel chip on my laptop and the
> >> permedia 2 on my server, neither could manage the necessary dot clock
> >> rate.
> >>
> >> to fit inside a standard plastic scart plug. However my experiments
> >> I suspect the 20-230MHz range of the driver is caused by a hardware
> >> limitation, rather than an issue with the software. Your best bet is
> >> probably something like
> >> http://www.maplin.co.uk/Module.aspx?ModuleNo=35258, which essentially
> >> does the same thing that the tv out hardware on many graphics adapters
> >> does, ie it converts the signal down to something the TV can cope with
> >> so that the graphics card doesn't need too.
> >>
> >> Tim W
> >
> > Hi Tim,
> >
> > Thanks for your answer!
> >
> > I have a cable just like that one so that would be my first option to
> > use. I could use a converter, but in that case I would like it to be a
> > little bit better. I would like it to follow the refresh rate of the
> > input, 50 or 60Hz and to have scart output or component.
> >
> > One id?a would be to double the dot clock and the horizontal resolution
> > with a 1440x576 at 50i mode. I have found some positive feedback on that so
> > i tried to get i working. But get a "vertical timing out of range" for
> > that mode.
> >
> > Where can I find supported timings, dot clocks, etc for the vx800?
>
> I've used the 1440x576 trick, not because the card I was using didn't
> support the low dot clock, but because it seemed to give a slightly
> better picture (although that could be my imagination - I can't explain
> it). All you have to do is take a correctly timed 720x576 mode and
> double the clock plus all the horizontal values, leaving vertical
> unchanged.
>
> Here's some modes I have had work:
> ModeLine "1440x576" 27.0 1440 1464 1590 1728  576 581 586 625 interlace
> -hsync -vsync
> ModeLine "1440x576" 28.0 1440 1518 1648 1792  576 581 586 625 interlace
> -hsync -vsync
>
> I haven't had much luck with nVidia cards, but some ATI cards/chips work
> fine using the radeon driver (not radeonhd).  A really good choice is
> a mobo with an integrated X1250. Works beautifully.
>
> Cheers,
> 	Paul.

Hi Paul,

Thanks for your answer. I've laborated a bit more now. It seems the 1440x570 
mode is the way to go, but sadly there doesn't seem to be support for 
interlaced mode in the Via vx800, at least not from the current driver. I have 
to investigate if it's a hardware limitation.

/Anders