X server Resolution Catch-22 Fedora 12
Adam Jackson
ajax at redhat.com
Mon Nov 23 20:51:27 UTC 2009
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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