Problem with DVI throughput

From ThinkWiki
Revision as of 12:08, 10 May 2005 by 217.231.106.144 (Talk)

Jump to: navigation, search

Information about the DVI throughput problem on port replicators and docks with Thinkpads from approximately 2000-2004.

Problem description

All Thinkpad port replicators and docking stations support a maximum resolution of 1280x1024 on the replicators/docks DVI port. Resolutions above are not supported in standard drivers at all and lead to random screen corruption if used with modified or alternative drivers.

Random screen corruption means that approximately 1 out of 5 times you will have a lot ot flickering blue and green pixels (roughly gathered to vertical stripes) on your DVI driven display.

I also discovered the phenomena of an unsharp picture when having automatic picture expansion enabled on my 1600x1200px display. Switching this off recovers the picture quality.

It is not entirely clear so far if the screen corruption problems are a driver or hardware problem.

Affected Models

Affected Operating Systems

  • Linux, all flavours
  • Windows, all flavours

Status

IBM knows about this and has included this limitation into the specs of all these docking solutions.

It is possible to run higher resolutions on the DVI port. Linux supports this natively. With Windows you need to install an alternative driver for the ATI graphics card since the IBM driver doesn't support higher resolutions than 1280x1024 on DVI. Also one can do some registry hacking to make the higher resolutions available in the Presentation Manager.

However, on both displays still remains the phenoma of random screen corruption.

Solutions

Linux

Under Linux, you can in theory make use of higher resolutions. (This is currently limited by the unability of drivers to use the DVI port.) If screen corruption should occur, you can try fixing it by changing from X to the console and back. Doing this often helps.

Windows

The solution to the Windows driver problem can be found in patched ATI driver sets like DNA-ATI or OMEGA drivers.

Also, Dax Kelson posted this mail in the Linux-Thinkpad Mailinglist. The tool he recommends solves the problem indeed, but introduces the new problem, that you can't use resolutions of 1400x1050 px anymore, since this is a notebook only resolution which is not supported by the standard Catalyst drivers.

The remaining problem with Windows is that IBMs practical Presentation Director utility still doesn't support the higher resolution. This issue is solvable by doing some manual modifications to Presentation Directors registry entries. If you don't want to tweak your registry you can use multi-res (packaged with the OMEGA drivers) instead of Presentation Director.

If you want to use Presentation Director, follow this procedure:

  • Add a profile with VGA output and set it to 1600x1200.
  • Then you also add a profile with DVI output and set it to 1280x1024.
  • After finishing the wizard you open regedit.
  • Look for the Presentation directors key structure (HKEY_CURRENT_USER/Software/IBM/NPdirect/Data/Common/Presentation/Schemes) and
  • copy the resolution value from the VGA profile to the DVI profile. (So if your VGA profiles name is VGAprof and the DVI profiles is DVIprof, you copy the Resolution keys value from HKEY_CURRENT_USER/Software/IBM/NPdirect/Data/Common/Presentation Schemes/VGAprof/01 to ....../DVIprof/01.)
  • Close regedit (and eventually reboot) and restart Presentation Director.
  • You should be have the wanted resolution in the properties of your DVI profile.