Christian Zeitnitz

Screen Resolution with Intel Graphics and HDMI TV

My multi media PC which connects to the flat screen TV via HDMI runs on Intels Mobile GMA 965 graphics. When booting the PC and with a switched on TV everything worked fine. The monitors EDID information is used and the screen resolution set correctly (in my case 720p). Problems show up, when the TV is switched on too late or after the PC was in standby mode. In these case the screen resolution was reset to VGA, which is pretty useless for a media center

To solve this problem one has to add each of the possible and wanted screen resolutions as non-EDID Detailed Timing Descriptors (DTD) to the driver definitions. There are two possibilities to do this:

• Edit the drivers inf file (igdlh.inf) before the installation
• Add the information directly in the registry

You should be aware of the supported resolutions of your screen. You can use a program like MonInfo to read the EDID information and obtain a list of the supported formats (interlaced and native).

Edit the igdlh.inf file

The file igdlh.inf contains a section for non-EDID DTD lines.

[NonEDIDMode_AddSwSettings]
HKR,, TotalDTDCount, %REG_DWORD%, 0      ; This shows number of DTDs to be used. ;  0-->Disable the feature.
;Following keys have 20 bytes (18 byte DTD + 2 Byte flags).
HKR,, DTD_1,%REG_BINARY%, 01,1D,80,18,71,1C,16,20,58,2C,1A,00,00,00,00,00,00,86,37,01        ;1920x1080@60...Interlaced
HKR,, DTD_2, %REG_BINARY%, 01,1D,80,D0,72,1C,16,20,10,2C,1A,80,00,00,00,00,00,86,37, 01        ;1920x1080@50...Interlaced
HKR,, DTD_3,%REG_BINARY%, 01,1D,00,BC,52,D0,1E,20,B8,28,25,40,00,00,00,00,00,04,37, 01        ;1280x720@50....Non-interlaced
HKR,, DTD_4, %REG_BINARY%, 01,1D,00,72,51,D0,1E,20,6E,28,25,00,00,00,00,00,00,06,37,01        ;1280x720@60....Non-interlaced
HKR,, DTD_5,%REG_BINARY%, 00, 00, 00 ,00, 00, 00,00, 00, 00,00, 00, 00,00, 00, 00,00, 00, 00,00, 00    ;Fifth DTD

The original version contains a value of 0 for the key TotalDTDCount. Changing this in the above example to 4 will enable the timing lines DTD_1 to DTD_4. In this case 1080i with 50 and 60Hz and the two non-interlaced 720p lines.
After the installation these modes should be available independent of the EDID information.

Adding DTD information to the Registry

If you are not willing to re-install the driver you can just add the required information to the registry manually.

• Start regedit
• Search for all occurences of TotalDTDCount and change the value to the number of DTD entries you like to add. Be sure to change ALL TotalDTDCount in the registry!
• Search for DTD_1 and replace the content (type is REG_BINARY) with the hex codes needed for your screen. Again be sure to overwrite ALL occurences in the registry!
• Repeat for all other required DTD entries
• Reboot the PC and enjoy!

Modifying the registry can damage your Windows installation and can render it useless. Edit the registry at your own risk and only when you know what you are doing!