Hello,
A recent "bug" in XF86Setup made me wonder... (I think it wasn't a bug,
and not a recent occurance either, btw)
How does an LCD screen work? XF86Setup generates modelines with a 65.15
dot clock for any resolution I select, which turns out "invalid" for any
resolution other than 1024x768. I am beginning to believe this is
because it is the fixed dot clock at which the display card communicates
with the screen. (This is pure speculation on my part.) The hsync and
vsync restrictions are then probably completely useless - except for
making perfectly valid modes appear invalid? Does this make sense?
I have been wondering what hsync and vsync I'm supposed to specify with
my LCD screen, realising that hsync and vsync is possibly pointless in
the LCD world, but this is the first time I came up with this idea. I
didn't find anything in the Laptop HOWTO or the XFree86 Video Timings
HOWTO about LCD screens.
I have thrown a bunch of modelines into my XF86Config file, from 320x200
to 1024x768 (all the modelines generated by xf86config up to 1024x768),
set my HorizSync to 31.5-57 and VertRefresh to 50-90 (no specific
reason), and fired up XF86_SVGA (MACH64 "melts" my display if I use
anything other than 1024x768). All the modes work very nicely... Then I
fireup xvidtune, it claims 65.15 dotclock for all modes, 101.79kHz
Horizontal Sync, 427.69Hz Vertical Sync. If this is so, laptop X
configurations can be a lot simpler than they are, with just the extra
bit of documentation ("Select maximum hsync and vsync"), or minimal
programming (for laptops who's "fixed" dotclock can be detected this
easily). What I'm wondering is if any timing parameters in the Modelines
are relevant except for HorizResolution and VertResolution? I don't feel
like messing with that too much at the moment though.
My laptop has an ATI Rage Mobility display card, btw. There is a second
Pentium 120 laptop with a C&T card in my household, I'll have a look at
that one later, and see if it works similarly.
Any ideas? Should I have rather directed this email at /dev/null? All in
the quest for better laptop support in Debian... Linux for that matter.
Thanks,
Hugo van der Merwe
