Cannot get 75hz on TFT monitor

[Matthias Hopf]

On Oct 31, 05 15:44:03 +0100, Erik Ahlner wrote:
> Michel Dänzer wrote:
> >>So, there's something jiffy about DVI.. it works in 75hz in windows, but 
> >>in Xorg, it just gives me 60.
> >
> >The panel probably runs at 60 Hz anyway, so that should be ideal.
> >
> No, it does *not* run at 60hz. There's a VERY noticable difference 

Yes, it (presumably) does.
The effect you're seeing is from not having a sync-to-vblank on the
computer framebuffer side, but only on the panel internal framebuffer.

If you run your VGA at 60Hz the panel can either directly use the input
signal, or sample into its internal framebuffer which is then scanned
out. In both cases you see the data exactly as released by the graphics
card, which includes tearing due to missing sync-to-vblank.

If the VGA runs at 75Hz, the data is always sampled into the internal
framebuffer of the panel, which is typically double buffered and is
synced to vblank (of the internal 60Hz sampling).
If the panel wouldn't have a double buffer, you would see tearing in
this case as well.

Personally, I dislike having the panel run at a different frequency due
to studdering effects, but for Quake 1 you should be pretty close to
77Hz, right.

There are few panels that can scan out at different frequencies than
60Hz, and even fewer at higher frequencies.  My projector is optimized for
video, and thus can scan out at 47.952, 48, 50, 59.94 and 60 Hz, but
not at 75Hz.

Matthias

-- 
Matthias Hopf <mhopf at suse.de>       __        __   __
Maxfeldstr. 5 / 90409 Nuernberg    (_   | |  (_   |__         mat at mshopf.de
Phone +49-911-74053-715            __)  |_|  __)  |__  labs   www.mshopf.de