editing xorg.config for uncommon display settings

Stereo-Farmer · 08-29-2009, 12:29 AM

Hi,

I am using freespire 2.0 with an old (very old) monitor.
I get an extremely distorted picture, it shows mirror images that overlap instead of a normal desktop.

I know that this monitor will display correctly at 1024 x 768 interlaced 43 Hz vertical refresh rate. I have seen this in windows.... but I want to use linux,

I have tried editing xorg.config as root to my desired settings twice, one time did nothing and the other time made the system crash each time the X server was started, so I obviously did it wrong.

So my question is what would be the proper way to edit xorg.conf? What would the mode line look like and where should it be located in the script? (what section/subsection?)

jschiwal · 08-29-2009, 01:33 AM

Check your monitor's specs. Are the vertical and horizontal rates in xorg.conf reasonable? 43 Hz seems a little strange.

You can generate a custom mode line with: gtf 1024 768 43 -x

Remove the ".00" from "43.00" in the modeline before adding it to xorg.conf. I once had a problem when I included it.

Stereo-Farmer · 08-29-2009, 12:53 PM

the settings I want are within my monitors specs, I realize 43Hz is odd but so is my monitor.

My main concern was getting the resolution interlaced, is that what the -x represents?

jschiwal · 08-30-2009, 12:37 AM

No. The -x option produces an org modeline instead of a frame buffer modeline.

Code:

> gtf 1024 768 60 -x

  # 1024x768 @ 60.00 Hz (GTF) hsync: 47.70 kHz; pclk: 64.11 MHz
  Modeline "1024x768_60.00"  64.11  1024 1080 1184 1344  768 769 772 795  -HSync +Vsync

> gtf 1024 768 60 -f

mode "1024x768 60.00Hz 32bit (GTF)"
    # PCLK: 64.11 MHz, H: 47.70 kHz, V: 60.00 Hz
    geometry 1024 768 1024 768 32
    timings 15598 160 56 23 1 104 3
    hsync low
    vsync high

From "Using Interlaced Modes" in the XFree86-Video Timings howto:

Quote:

Design of interlaced modes is easy: do it like a non-interlaced mode. Just two more considerations are necessary: you need an odd total number of vertical lines (the last number in your mode line), and when you specify the "interlace" flag, the actual vertical frame rate for your monitor doubles. Your monitor needs to support a 90Hz frame rate if the mode you specified looks like a 45Hz mode apart from the "Interlace" flag.

As an example, here is my modeline for 1024x768 interlaced: my Multisync 3D will support up to 90Hz vertical and 38kHz horizontal.

ModeLine "1024x768" 45 1024 1048 1208 1248 768 768 776 807 Interlace

This explains why the vertical rate seems low. It is counting the frame rate. The field rate is twice that.

Look in the X.org web site or you may have a linux howtos package you can install that contains the X.org howto's as well as others.