setmclk(1) Svgalib User Manual setmclk(1)NAMEsetmclk - adjust the memory timing of certain Cirrus cards.
This program sets the memory clock of Cirrus 5424/26/28 cards.
The first three values could be set by utility programs that came with
my card (AVGA3), but somewhat higher values seem to work (on my card at
least). It may be that better and more recent Cirrus cards use a higher
value as boot-up default. It should depend on DRAM speed, but it seems
to be more dependant on the card logic.
I have the impression that many Cirrus 542x cards suffer from horrible
BIOS version/DRAM timing misconfigurations. Perhaps even some versions
of MS-Windows drivers change the MCLK register. In any case, the boot-
up BIOS default (0x1c) may be inappropriately low for the type of DRAM
timing most cards use.
Using a higher memory clock gives a very significant performance
improvement; with high dot clock modes (like 640x480x16M or
1150x900x256) performance can be more than twice that of the standard
50 MHz clock. This goes for both (VLB) framebuffer access and acceler‐
ated features (bitblt). This also helps XFree86 server performance, but
only if the XFree86 Cirrus driver doesn't set the memory clock register
(it should work for XFree86 1.3 and 2.0). Use at your own risk!
Note that the dot clock is something entirely different. There does not
seem to be much correlation between the two (i.e. if a high dot clock
gives screen problems, using a high memory clock is not likely to fix
it, other than improving speed).
The actual memory clock is hard compiled into the program. It defaults
to 0x1c. You can change this value and some suggestiong come in th
source of the utility.
This utility is part of svgalib and can be found in the utils/ subdi‐
rectory of the original svgalib distribution. However, it is not
installed by default, s.t. it is unclear where you can find it if your
svgalib was install linux distribution.
In case of any such problem, simply get an svgalib distribution from
the net. You don't need to install it. Just make in the utils/ subdi‐
recty. As of this writing, svgalib-1.2.12.tar.gz is the latest version
and can be retrieved by ftp from sunsite.unc.edu at
/pub/Linux/libs/graphics and tsx-11.mit.edu at /pub/linux/sources/libs
which will most probably be mirrored by a site close to you.
SEE ALSOsvgalib(7), vgagl(7), libvga.config(5), convfont(1), dumpreg(1),
restorefont(1), restorepalette(1), restoretextmode(1), runx(1),
savetextmode(1), fix132x43(1), textmode(1).
This manual page was edited by Michael Weller <firstname.lastname@example.org-
essen.de>. The exact source of the referenced utility as well as of the
original documentation is unknown.
It is very likely that both are at least to some extent are due to Harm
Occasionally this might be wrong. I hereby asked to be excused by the
original author and will happily accept any additions or corrections to
this first version of the svgalib manual.
Svgalib (>= 1.2.11) 2 Aug 1997 setmclk(1)