








		 Information for Western Digital Chipset Users

			   The XFree86 Project, Inc.

				  14 July 1995



1.  Supported chipsets

XFree86 supports the following Western Digital SVGA chipsets: PVGA1, WD90C00,
WD90C10, WD90C11, WD90C24, WD90C30, WD90C31, WD90C33.  Note that the rest of
the WD90C2x series of LCD-controller chipsets are still not supported.	The
WD90C24 family is now supported including acceleration, adjustable clocks and a
full 1MB video ram even on dual scan systems (in CRT mode).  If you have trou-
ble with the new WD90C24 support (not that we expect you will), try specifying
"wd90c30" or "wd90c31" on the `Chipset' line in your XF86Config file.  The
WD90C24, WD90C31 and WD90C33 are supported as an accelerated chipset in the
SVGA server; the accelerated features are automatically activated when a
WD90C24, WD90C31 or WD90C33 is detected, or specified in the XF86Config file.


2.  Special considerations

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 `Clocks' line in your XF86Config
file, you should comment it out, and rerun the server with the `-probeonly'
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 detect 17 clocks for the WD90C24, WD90C30 and WD90C31 chipsets.
If you have one of these chipsets, you should let the server re-probe the
clocks and update your XF86Config.

There is an `Option' flag available for the XF86Config file that is specific to
the Western Digital chipsets (except the WD90C24).  This option is
"swap_hibit".  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 "swap_hibit" 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.





 Information for Western Digital Chipset Users





 Information for Western Digital Chipset Users



3.  WD90C24 features

These next three sections apply only if you have a WD90C24, WD90C24a, or
WD90C24a2 and don't specify some other chipset in your XF86Config file.  The
SVGA pvga1 driver now recognizes the wd90c24 family as different from the
WD90C30 and seems to resolve most of the problems people encountered when these
chips were treated as WD90C3X.	The new code has the following features:

   o Locks the shadow registers at appropriate times; This should prevent
     scrambled displays after exiting X with dual scan screens when simultane-
     ous or LCD display mode is selected.  The code does depend somewhat on the
     behavior of the BIOS regarding when it locks the shadow registers, etc.

   o Allows (forces) the use of a full 1 Meg VRAM for dual scan systems when
     the server is started while external CRT only display is in operation.
     This allows 1024x768x8 resolution.

   o If the XF86Config file specifies a virtual screen size which requires more
     than 512 K VRAM when the server is started on a Dual Scan LCD, the driver
     will force the virtual size to 640x480.  This eliminates the need to edit
     the XF86Config file when you switch from 1024x resolution on the CRT, to
     or from the LCD screen.  If no virtual size is specified, the result will
     be 800x600 virtual in LCD modes and 1024x768 in CRT only mode (so you have
     a choice).

   o Note that on dual scan systems, you must still exit X, switch displays,
     and restart X to change to/from CRT only with 1 Meg videoram.  This is
     because once the server starts, you can't change the virtual screen size.
     There is no way around this with the current server and the WD90C24 with
     dual scan displays.  The WD90C24 requires half the videoram be used for a
     ``Frame buffer'' when the dual scan LCD is in use.

   o The new server uses the accelerated features of the WD90C24a.  It is not
     clear from the data book if the WD90C24 also supports ALL the required
     features.	Several people have stated that the WD90C24 is not accelerated,
     but the differences section of the WD90c24a data book implies that they
     ARE all three accelerated.  The differences documented with regard to
     acceleration are with the type of line drawing the hardware does; Only the
     newer chips support the type of line drawing that MS windows wants.  This
     may be what has caused the confusion since the accelerated windows drivers
     may only support the WD90c24a chips.  If this turns out to be a problem
     with the WD90C24, acceleration can be disabled by adding the line:

		Option "noaccel"



     to the Device section of the XF86Config file.

   o Although the new server does not support programmable clocks in the same
     way as some of the other servers, 8 of the 17 clocks may be set to
     (almost) any value via the Clocks line. It also supports options for
     adjusting the VRAM clock.









 Information for Western Digital Chipset Users



4.  WD90C24 clocks

Here are some more details on the adjustable clocks:

The VRAM clock (Mclk) is adjusted by adding ONE of the following option lines
to the Device section of the XF86Config:

	Option	    "slow_dram"     # Set Mclk to 47.429 MHz
	Option	    "med_dram"	    # Set Mclk to 49.219 MHz
	Option	    "fast_dram"     # Set Mclk to 55.035 MHz


The default is to leave Mclk as the BIOS sets it.  This is 44.297 on many sys-
tems.  Some systems may not work properly with any of these options.  If you
experience ``bit errors'' on your display, reduce the Mclk speed, or don't use
any of these options.  The Mclk is not reset on server exit.

The data book says that the maximum pixel clock is 1.6 times Mclk so you may
want to experiment with higher Mclk rates if you have a fast monitor.  It also
says a 44.297MHz Mclk and 65MHz pixel clock is the fastest the WD90C24A2 is
designed to go.  However, some success has been reported with faster clocks.
Don't expect all the clocks the chip can provide to work properly.

The second and fourth group of 4 clocks are adjustable.  That is, clocks 5, 6,
7, 8 and 13, 14, 15, 16 (counting from 1).  These clocks are set by the Clocks
line.  Be sure to adjust the 17th (last) clock to match your Mclk.  Here is a
sample set of clocks lines with some clocks defined which are not directly pro-
vided by the chip.  The NON-programmable clocks (1-4 and 9-12) MUST be set as
indicated here.

	Clocks	   25.175 28.322 65	36     # These are *not* programmable

	Clocks	   29.979 77.408 62.195 59.957 # these are programmable
	Clocks	   31.5   35.501 75.166 50.114 # these are *not* programmable
	Clocks	   39.822 72.038 44.744 80.092 # these are programmable
	Clocks	   44.297		       # Change this if you change
					       #   Mclk above.

You can program the clocks in increments of .447443 MHz.  The server will warn
you and adjust to the nearest increment if you specify a clock which does not
fit this formula.  Clocks 1-4 and 9-12 (the fixed clocks) are not constrained
to this multiple, but instead are used to provide standard clocks which are not
a multiple by .447443 MHz.

If you probe for clocks (for example to find your Mclk), do it in CRT only mode
and then add clocks lines in your XF86Config file.  Clocks will not probe cor-
rectly in LCD mode on most systems.

The BIOS on some systems may not allow switching from CRT to LCD unless the
correct clock and/or mode is used.  Try the following mode line for 640x480 LCD
displays.

	ModeLine "640x480"  25.175   640 664 760 800	 480 491 493 525 #CRT/LCD









 Information for Western Digital Chipset Users



The following modelines have been tested with the above Clocks lines on some
systems, and are provided here as examples. Some testers have experienced minor
problems (snow) with the fixed 65 and 75.166 MHz dot clocks.  The modelines
below have been reported to circumvent these problems.	Do not assume your mon-
itor will not be damaged by any of these.

      # VESA 800x600@72Hz Non-Interlaced mode
	ModeLine  "800x600.50"	50  800  856  976 1040 600 637 643 666	+hsync +vsync


      # 1024x768  Interlaced mode
	ModeLine  "1024x768i"	45  1024 1048 1208 1264 768 776 784 817 +hsync +vsync Interlace

      # 1024x768@60Hz Non-interlaced Mode
      # One of the dram options may be necessary
	ModeLine  "1024x768.65" 65  1024 1032 1176 1344 768 771 777 806 -hsync -vsync


      # 1024x768@60Hz Non-Interlaced mode (non-standard dot-clock)
      # Seems to work without dram options
	ModeLine  "1024x768.62" 62  1024 1064 1240 1280 768 774 776 808

      # 1024x768@70Hz Non-Interlaced mode (non-standard dot-clock)
      # May need fast_dram option
	ModeLine  "1024x768.72" 72  1024 1056 1192 1280 768 770 776 806 -hsync -vsync


5.  Additional WD90C24 information

Standard disclaimers apply.  Use this driver at your own risk.	If you need
additional information on using XFree86 with the WD90C24 family however, you
might try Darin Ernst's home page <URL:http://www.castle.net/~darin>.  Darin
maintains a mini-HOWTO on ``X and the WD90C24''. He was the first tester of the
WD90C24 code and provided many good ideas and encouragement.  You can reach
Darin at darin@castle.net or dernst@pppl.gov.  I only provided the WD90C24 spe-
cific code.  You can reach me (Brad Bosch) at brad@Lachman.com.

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 Information for Western Digital Chipset Users





































































				   CONTENTS



1. Supported chipsets  ...................................................... 1

2. Special considerations  .................................................. 1

3. WD90C24 features  ........................................................ 2

4. WD90C24 clocks  .......................................................... 3

5. Additional WD90C24 information  .......................................... 4











































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