On Sat, Sep 12, 2009 at 1:11 PM, Csillag Kristof<[email protected]> wrote: > Dear all, > > Now that the CustomEDID support is (mostly) in place, > I can force my card to output the proper data, > even when the monitor is connected via DVI. > > According to the X log, the selected mode is correct > (ie. it is the same as the mode I get when I connect > via VGA.) The OSD menu of the monitor confirms this. > > However, despite the fact the the output mode seems to be correct, > the image on the display is twitching. It's only happening > once or twice a minute, but it's still annoying. > > Furthermore, the first time I have tried the CustomEDID > code, there were some random red dots scattered on the screen, > appearing and disappearing back to nothingness, really fast. > (Something like static on the TV screen, but only in red, > with fewer artifacts, scattered over the normal image.) > > I have changed the DVI cable, and the red dots went away, > but the twitching has remained. > > What could be the reason for this? > > I know the monitor can be driven via DVI, since it works flawlessy > with my office notebook (which has an NVIDIA chip built in.) > > * * * > > So here is what I know: > > - VGA connection with the radeon card works > - DVI connection with the NVIDIA card works > - DVI connection with the radeon card works, but with twitching. > > All above cases use the same modeline > > If the monitor is OK (as proven by the NVIDIA case, > and the mode is right (as proven by the NVIDIA case and the VGA case), > what can be wrong? > > One thing that bothers me is that the bandwidth required by the mode > (1600x1200, 60Hz) is 161 Mhz, dangerously close to the 165 Mhz > maximum bandwidth of a single-link DVI connection. > > Could it be that I am running into low-level signal transmission issues > here? > > Previously I thought that DVI belongs to the digital world, so > things are black and white: either we have a connection, > or we don't have one, with no third choice in-between. > > Maybe this was a false assumption, and as we get close to the maximum > bandwidth, the analog hell creeps back? > > I have run some tests, and I have weed out more than half > of my el-cheapo DVI cable collection I usually use, > and the twitching definitly got better, but it is still there > sometimes. (Strangely, the picture data seems to influence > the frequency.) The red dots disappeared completely. > > I have also noticed that removing the display switch > from the settings improves the situation, but does > not rectify it completely. > > * * * > > But then again, the NVIDIA card could drive the monitor properly, > using the same cables, switch and everything. > > What should I think of that, then? > > This is pure speculation (and I don't have an oscilloscope > to check it ouy), but could it be that the NVIDIA operates > with somewhat higher signal voltages (or sharper signals), > which get through the poor-quality cabling, where the weeker > signals from the radeon get sometimes mingled? > > Is there any way I can influence the lowest level > of the signal transmission done by the card? > (Signal voltage, timings, etc.) > > Do you have any advice?
This is likely display watermark or pll related. Please try xf86-video-ati from git master as that has proper watermark setup implemented and support for fractional feedback dividers. If you are still having problems with master, please try: Option "DisplayPriority" "HIGH" in the device section of your config. Alex _______________________________________________ xorg mailing list [email protected] http://lists.freedesktop.org/mailman/listinfo/xorg
