Posted: . At: 10:21 AM. This was 4 years ago. Post ID: 14431
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How to calculate VESA GTF modelines with the command line on Linux.

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Gtf is a utility for calculating VESA GTF modes. Given the desired horizontal and vertical resolutions and refresh rate (in Hz), the parameters for a matching VESA GTF mode are printed out. Two output formats are supported: mode lines suitable for the Xorg xorg.conf(5) file, and mode parameters suitable for the Linux fbset(8) utility.

This is an example, creating a modeline for a monitor to use a 1920×1080 pixels resolution at 75 HZ.

4.4 Tue Jun 23 jason@Yog-Sothoth 0: $ gtf 1920 1080 75
 
  # 1920x1080 @ 75.00 Hz (GTF) hsync: 84.60 kHz; pclk: 220.64 MHz
  Modeline "1920x1080_75.00"  220.64  1920 2056 2264 2608  1080 1081 1084 1128  -HSync +Vsync

This might be a bit outdated these days. but it could be possible that someone wanted to use a CRT on a modern PC, for example, an old CRT and it is not autodetected.

Here is another example.

4.4 Tue Jun 23 jason@Yog-Sothoth 0: $ gtf 2048 1536 85
 
  # 2048x1536 @ 85.00 Hz (GTF) hsync: 137.02 kHz; pclk: 388.04 MHz
  Modeline "2048x1536_85.00"  388.04  2048 2216 2440 2832  1536 1537 1540 1612  -HSync +Vsync

This resolution can then be tested with xrandr.

4.4 Tue Jun 23 jason@Yog-Sothoth 0: $ xrandr -newmode "2048x1536_85.00"  388.04  2048 2216 2440 2832  1536 1537 1540 1612  -HSync +Vsync

Then if it works, it can be used in the xorg.conf to define a monitor resolution that works just fine.


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