  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 trouble 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.

  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 simultaneous 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.

  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 systems.  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 provided 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 correctly 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



  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 monitor 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
  <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
  specific code.  You can reach me (Brad Bosch) at brad@Lachman.com.


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