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<title> Information for Western Digital Chipset Users
<author> The XFree86 Project, Inc.
<date> 16 December 1994
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<sect> Supported chipsets <p>
XFree86 supports the following Western Digital SVGA chipsets: PVGA1,
WD90C00, WD90C10, WD90C11, WD90C30, WD90C31, WD90C33.  Note that the
WD90C2x series of LCD-controller chipsets (common on laptops) is still not
supported.  The WD90C24 is an exception to this.  It appears to be
compatible with the WD90C30, and the server will treat it as one of
these.  The WD90C24A is compatible with the WD90C31.  To use it, add a
`<tt>Chipset "wd90c31"</tt>' to your <tt>XF86Config</tt> file.
There may be some problems on
some OSs when returning to text mode when using the WD90C24.  The WD90C31
and WD90C33 are now supported as an accelerated chipset in the SVGA
server; the accelerated features are automatically activated when a
WD90C31 or WD90C33 is detected, or specified in the <tt>XF86Config</tt> file.

<sect> Special considerations <p>
All of the Western Digital chipsets after the PVGA1 support the ability
to use the memory-refresh clock as an alternate dot-clock for video
timing.  Hence for all of these chipsets, the server will detect one more
clocks than ``normal''.  What this means is that if you have an old
`<tt>Clocks</tt>'
line in your <tt>XF86Config</tt> file, you should comment it out, and rerun
the server with the `<tt>-probeonly</tt>' option to find all of the clock
values.  All but the
last should be the same as what you had before; the last will be new.

For the WD90C00 chipset, the chipset will only support 640x480 in 256-color
mode.  Even though 512k of memory should allow better than 800x600, the
chipset itself cannot do this.  This is stated in the databook (which lists
1024x768x16 and 640x480x256 for specifications).  We have also witnessed
this behavior.

The server will now detect 17 clocks for the WD90C30 and WD90C31 chipsets.
If you have one of these chipsets, you should let the server re-probe the
clocks and update your <tt>XF86Config</tt>.

There is an `<tt>Option</tt>' flag available for the <tt>XF86Config</tt>
file that is specific to the Western Digital chipsets.
This option is <tt>"swap_hibit"</tt>.  We have
determined via experimentation that the WD90C1x and WD90C3x chipsets need
the high-order clock-select bit inverted, and the PVGA1 and WD90C00 need it
non-inverted.  This is hardcoded into the driver.  Since our sample-set was
rather small, we have provided the <tt>"swap_hibit"</tt> option to invert
this behavior.
If the clocks detected by the server show a very low last clock
(under 28Mhz), then this option is likely needed.

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$XFree86: xc/programs/Xserver/hw/xfree86/doc/sgml/WstDig.sgml,v 3.1 1995/01/11 09:47:54 dawes Exp $
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