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Re: X server Resolution Catch-22 Fedora 12



On Mon, 2009-11-23 at 12:59 -0700, Michal Jaegermann wrote:

> If we are already there then maybe you can explain? :-)
> 
> 'man -k mode | grep VESA' prints
> 
> cvt []               (1)  - calculate VESA CVT mode lines
> gtf []               (1)  - calculate VESA GTF mode lines
> 
> but what is a difference?  'man cvt' at least says "VESA Coordinated
> Video Timing".  V.E.R.A. for a change brings "Generalized Timing
> Format (VESA)" when asked for "gtf".  I am afraid that this still
> does not tell me very much.  Results with the same paramaters are
> slightly different.  'xvidtune' allows to "tune" an image to your
> monitor before you will hit "Show".

They're both timing generation formulas.  GTF is older, a bit more
complex, and generally matches the physical requirements of CRTs.  CVT
is newer, simpler, and has a cheat code for reduced bandwidth
consumption on LCDs.  This is important, among other reasons, because
the DVI link speed is 165MHz:

atropine:~% cvt 1920 1200 60
# 1920x1200 59.88 Hz (CVT 2.30MA) hsync: 74.56 kHz; pclk: 193.25 MHz
Modeline "1920x1200_60.00"  193.25  1920 2056 2256 2592  1200 1203 1209 1245 -hsync +vsync
atropine:~% cvt -r 1920 1200 60
# 1920x1200 59.95 Hz (CVT 2.30MA-R) hsync: 74.04 kHz; pclk: 154.00 MHz
Modeline "1920x1200R"  154.00  1920 1968 2000 2080  1200 1203 1209 1235 +hsync -vsync

and so a non-reduced-blanking timing for 1920x1200 won't fit on a single
DVI link.

tl;dr version: GTF for CRTs, CVT for LCDs.

- ajax

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