Configuring X.Org Display Resolutions Under Ubuntu 8.04

Problems with High Resolution Monitors and X.Org

I recently bought a 28′ LCD Monitor, the I-INC iF281D. I bought the monitor to increase my usable desktop workspace on my Ubuntu 8.04 (Hardy) Linux workstation. I do a lot of programming, systems administration, log analysis and monitoring – and I usually have three or more X Terminals open at any one time (with some mixture of “top”, “vim”, “tail”, and “screen” open), so the more desktop space I have, the better.

When I first attempted to configure my new monitor using the ‘nvidia-settings’ GUI application that comes with NVIDIA’s Linux driver, I noticed that it didn’t present all the resolutions that the monitor supported.  NVIDIA’s Settings GUI was limiting the available resolutions to a maximum of 1280×800. This was odd, because the monitor supported resolutions up to 1920×1200, and supported DCC, so the GUI should have been able to pick up the monitor specifications and provide configuration options for all supported features (resolutions, refresh rates, etc.)

At first I thought that the problem was with the NVIDIA driver I was using, and so I downloaded the latest driver from NVIDIA’s website, recompiled and tried again.  I still however was not able to get the resolutions that the monitor supported.


My 28 Inch Desktop @ 1920x1200

Solving The Problem

After much more digging and research, I found that the problem was not with the monitor, or the NVIDIA driver, but with the mode settings in ‘xorg.conf’. What I wasn’t aware of was that the Horizontal Sync rate definition within my ‘xorg.conf’ directly reflects the resolutions that will be available to me.

For example, the ‘nvidia-settings’ application set the Horizontal Sync and Vertical Refresh to low (safe) values by default. Therefore the available resolutions were limited. Once I figured out what my maximum HZ Sync and VT Refresh were, I was able to achieve the resolutions that the monitor was capable of.

There are Xfree86 Video Timing HOWTO’s available if you want to get into the gory details of how to calculate the correct xorg.conf settings for your specific monitor. However, if you’re a programmer like me, then you’ll want to skip this step, expecting that someone else out there must have already been through this, and has likely created a tool to make our lives easier.

Lo and behold! Xtiming is a great web tool which helps you calculate your Horizontal Sync and Vertical Refresh Rate settings. Simply enter the resolution that you are trying to achieve, and Xtiming will tell you the settings you’ll need in your ‘xorg.conf’ file to get it.

For example, if you leave empty all the other values that Xtiming asks you for, and simply enter “1600×1200” for Visible Resolution, and “60” for Refresh Rate, then click “Calculate Modeline”; you’ll see that Xtiming returns the Mode Line that you should use, along with (and most importantly!) the Horizontal Sync rate you will need to achieve that resolution at the specified refresh rate:

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Modeline "1600x1200@60" 176.70 1600 1632 2296 2328 1200 1224 1236 1261
Horizontal sync frequency: 75.9 kHz

I personally found that I didn’t need to use the “Modeline”, but the Horizontal Sync Frequency was essential. Here’s an excerpt of my ‘xorg.conf’ file using the above settings:

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(...)
 
Section "Monitor"
 
    # HorizSync source: xconfig, VertRefresh source: xconfig
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "AUO"
    HorizSync       30.0 - 75.9
    VertRefresh     60.0
    Option         "DPMS"
EndSection
 
(...)
 
Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "TwinViewXineramaInfoOrder" "DFP-0"
    Option         "TwinView" "1"
    Option         "metamodes" "DFP-0: 1440x900 +1600+0, DFP-1: nvidia-auto-select +0+0"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

I’m using TwinView because I have a dual monitor setup. However, now that I have a 28′ display, dual displays don’t really seem to be a requirement any more :)

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