  Notes on the AGX Server
  Henry Worth
  24 June 1995

  1.  General Notes

  This server currently supports the IIT AGX-016, AGX-015, AGX-014 and
  XGA-2 chipsets. The AGX chipset is based on XGA architecture, but is
  missing several features and differs on others. There's also untested
  support for the XGA-1 and AGX-010 chipsets.  Pixel depths of 8bpp,
  15bpp, 16bpp are generally supported.  Unpacked 24bpp (RGBX 32bpp) is
  not yet stable enough to release.

  RAMDACs currently supported are the Brooktree (BT481, BT482, and
  BT485) and AT&T (20C505) RAMDACs used by the Hercules Graphite series,
  and Sierra RAMDACs (15025 and 15021), and Generic VGA RAMDAC. Untested
  support has been added for the AT&T 20C490 series.


  The current driver has a number of acceleration routines: solid and
  dashed zero-width lines (except AGX-014), bitblt fills, tiles, and
  stipples, solid arc and polygon fills, character glyphs and font cache
  for 8-bit characters.

  Boards that have had some testing include ISA and VLB versions of most
  of the Hercules Graphite series, Spider Black Widow VLB and Black
  Widow Plus VLB, Boca Vortek VL, CatsEye/X XGA-2, and the PS/2-57
  planar XGA-2. The Orchid Celsius is very similar to the Spider and
  Boca boards, except some batches may use one of the AT&T 20C490 series
  RAMDACs, instead of the Sierra 15025. There has also been a report of
  a generic board that uses a UMC RAMDAC that may be an AT&T 20C490
  Clone.

  2.  Acknowledgments

  First, to Hercules Customer Support for providing a loaner board to
  get things started.

  Second, to the XFree86 team, and those who who have contributed to
  their efforts to the project, for the foundation of work that provided
  a basis for bootstrapping this server.

  3.  Known Problems


     o  The accelerated line routines don't match lines written by the
        mi/cfb routines. This is noticeable when switching between
        virtual consoles while running routines that draw and erase
        lines. Seems to have been reduced/fixed in previous releases but
        need more testing.

     o  Some special-case speedup added to cached font rendering in
        3.1.1 has been disabled as is over-aggressive in some cases.
        This cuts the performance on terminal-fonts in half, and font
        performance is already low for the AGX chips compared to their
        contemporaries.

     o  As in all software, needs more testing.


  4.  ToDo


     o  Address the above known problems.


     o  Additional acceleration routines and general performance
        improvements. Many existing acceleration routines are Q&D
        adaptations of existing routines from other servers that support
        graphics chips that differ significantly, architecturally, from
        that XGA and are undoubtedly less than optimal. In particular
        some of the general per-operation overhead to set-up the
        graphics context should be moved to the ValidateGC() routines.

     o  Complete HW cursor support, most of the code is done (or
        borrowed from other servers). There just remains a little setup
        code and then finding a lot of time to debug and test the
        numerous permutations.

     o  Complete support for the Graphite Pro's 84-pin RAMDAC.  (the 2MB
        version of the Graphite Pro has both RAMDACs, the 1Mb only the
        44-pin RAMDAC). Currently, the 84-pin RAMDAC is only supported
        in clock-doubled pixmux mode, the server will switch between
        RAMDACs as required by the video mode In >8bpp modes this
        switching does not occur.

     o  Implement more HW probing, this will be difficult as it appears
        some (all?) AGX-based vendors don't implement the VESA VXE POS
        registers, although the AGX chip does support it (and some
        vendors claim VXE compliance...).  There are a few rev/vendor
        registers in the AGX chip but they are not documented. Note:
        SuperProbe also does not support probing for AGX/XGA chips. ISA
        POS probing is supported for the XGA chips and some code for
        EISA POS is also included but not tested.

     o  Micro-optimizations, in particularly reducing processing
        overhead for common special cases that don't require full
        generality.

  5.  XF86Config


  Device Section Entries and Options Currently Supported:

  The minimum that must be specified in the XF86Config device section
  for the AGX-014, AGX-015, AGX-016, and ISA-based XGA-1 and XGA-2 is
  the Chipset. However to get full capability out of the AGX-01[456]
  chips, the RAMDAC should be specified.  Other parms may select
  additional capabilities, or may used to override the defaults or
  reduce start-up time be suppressing probing. XGA specific
  configuration is covered at the end of this document. The XGA entries
  can generally be used to override defaults for the AGX-01[456] as
  well.


     Ramdac
        Be sure to check the clock rating of the RAMDAC(s) on your video
        board and don't exceed that rating even if the server allows it,
        overclocking RAMDACs will damage them.

        The clock rating generally appears as a suffix to the part
        number, may only have the most significant digit(s), and may be
        mixed with other codes (e.g. package type). For example, an
        85MHz Bt481 in a plastic J-lead package has a part number of
        Bt481KPJ85 and a 135MHz AT&T20C505 has a part number of
        ATT20C505-13. Sierra stamps the rated speed below the part
        numbers in a dark ink.


        "normal"
           normal VGA style RAMDAC (6-bit DAC), default if none

           specified. Most boards should work with this parm, but some
           capabilities will be unavailable. Only 8bpp is available.

        "bt481"
           bt481 RAMDAC (supports 8-bit DAC)

        "bt482"
           bt482 RAMDAC (supports 8-bit DAC) The Hercules Graphite HG210
           uses the BT481 or BT482, the only difference between these
           two is the BT482's HW cursor (not yet supported).  The
           BT481/2 are limited to 85Mhz.  8bpp, 15bpp, 16bpp are
           supported.

        "ATT20c490"
           AT&T490 RAMDAC (includes 49[123] - supports 8-bit DAC).
           Limited to 110Mhz at 8bpp. 8bpp, 15bpp, and 16bpp are
           supported.

        "SC15025"
           Sierra SC15025 and SC15021 RAMDAC (support 8-bit DAC). The
           SC15025 is limited to 125Mhz, and the SC15021 135Mhz. Check
           the RAMDAC's actual rating, some SC15025's used in AGX based
           boards are only rated to 110Mhz. 8bpp, 15bpp, and 16bpp are
           supported.

        "herc_dual_dac"
           Hercules Graphite Pro RAMDAC probe.  If the 84-pin Big-RAMDAC
           is installed (2MB models), will use the Big RAMDAC, but only
           clocks-doubled, pixel- multiplexed modes (higher clock values
           only!). Lower clocks and resolutions in 8bpp mode are
           supported by switching to the Small 44-pin RAMDAC. 15bpp and
           16bpp are supported.

           There has been one report of the "dac-8-bit" option not
           working with a Graphite Pro equipped with a BT485 RAMDAC,
           puzzling since it should be identical to the AT&T20C505 in
           this regard. No startup messages or XF86Config were submitted
           to aid problem isolation.

           Not supported by the HG210 Graphite.

        "herc_small_dac"
           Hercules Graphite Pro RAMDAC probe.  Forces use of only the
           BT481/482 RAMDAC. 8bpp, 15bpp, 16bpp, and unpacked 24/32bpp
           are supported.

           Not supported by the HG210 Graphite.

        "xga"
           To allow overriding the default VGA style RAMDAC control for
           the AGX-010.


     Ramdac related Option Flags:

        "dac_8_bit"
           Sets supported RAMDAC's to 8-bit DAC mode (all but "normal").

        "sync_on_green"
           Composite sync on green for RAMDAC's that support this
           feature (BT481/481 and AT&T20c490). However, whether any
           boards have necessary traces and glue logic is doubtful.




     Chipset:
        Must be specified, possible values: "AGX-016", "AGX-015",
        "AGX-014", "AGX-010", "XGA-2", or "XGA-1". Some AGX vendors
        place stickers over the chip, in general, if it's a VLB board
        it's probably an AGX-015 and if it's an ISA board it may be an
        AGX-014. The Hercules Graphite Power Pro and Spider Black Widow
        Plus use the AGX-016 chipset. In general, specifying a lower
        revision in the AGX-0{14,15,16} series does not seem to causes
        problems (except lower performance from the AGX-014's non-
        accelerated line drawing).

        Note: Only the AGX-016, AGX-015, AGX-014 and XGA-2 have had any
        testing. Most of the development has been with an AGX-015 based
        2MB Hercules Graphite VL PRO (HG720) and most of testers for
        previous releases had AGX-014 based 1MB Hercules Graphite
        (HG210).

        The limited documentation I have for the AGX-010 is that is is a
        clone of the XGA architecture with a few additional
        configuration registers. What is not clear is whether to use XGA
        or extended-VGA RAMDAC control registers.  The post-3.1.1
        default is now VGA control registers, but XGA control registers
        can be forced with the XGA RAMDAC parm.  Likewise the
        configuration parms described in the XGA section can be used to
        override the AGX defaults for I/O and memory addresses.

     VideoRam:
        Will be probed if not specified. The startup will be a little
        faster if specified.

     Tuning Option flags:

        Bus I/O interface:

           "8_bit_bus"
              Force 8-bit I/O bus.

           "wait_state", "no_wait_state"
              Set or clear CPU access wait state, default is the POST
              setting.

           "fifo_conserv"
              Disable Memory I/O Buffer, AGX-015 and AGX-016.  MS-
              Windows driver default. Required by some VLB systems with
              `aggressive timing'.  The default for this server is to
              disable the buffer.

           "fifo_moderate"
              Enable the AGX-015/016's Memory I/O buffer.

           "fifo_aggressive"
              Enable the AGX-016's extra-large buffer.  Either option
              may result in garbage being left about the screen,
              disabled by default.  A good test is the xbench or x11perf
              dashed lines tests, if random dots are drawn, fifo_conserv
              is required. So far, no boards have been reported that
              worked correctly with the buffers enabled.

        Memory Timing:
           POST defaults should be ok.


           "vram_delay_latch", "vram delay_ras", "vram_extend_ras",
              "slow_dram"
              Set all of the above vram options.

           "med_dram"
              Set vram latch delay, clear others.

           "fast_dram"
              All of the vram options are cleared.  Should be specified
              if directly specifying VRAM options in order to clear POST
              settings.

        Debugging:
           These shouldn't generally be required:


           "noaccel"
              (AGX,XGA) Disable Font Cache.

           "crtc_delay"
              (AGX) Force XGA mode CRTC delay.

           "engine_delay"
              AGX-015 only? adds additional VLB wait state.

           "vram_128", "vram_256"
              Sets VRAM shift frequency, vram_128 is for 128Kx8 VRAM.
              Default is to leave this bit unchanged from POST setting.

           "refresh_20", "refresh_25"
              Number of clock cycles between screen refreshes. Default
              is to leave this bit unchanged from POST setting.

           "screen_refresh"
              Disable screen refresh during non-blanked intervals,
              AGX-016. Default is leave them enabled.

           "vlb_a", "vlb_b"
              VLB transaction type, default is to leave this bit
              unchanged from POST value.


     Virtual resolution:
        The server now accepts any virtual width, however the actual
        usable CRTC line width is restricted when using the graphics
        engine and depends upon the chip revision. The CRTC line width
        and not the virtual width determine the amount of memory used.
        The server currently does not make use of any of the unused CRTC
        line's memory. CRTC line width is restricted by the following
        rules:


          AGX-014 : 512, 1024 and 2048. (also AGX-010)


          AGX-015 : 512, 1024, 1280, and 2048.


          AGX-016 : 512, 640, 800, 1024, 1280, and 2048.


          XGA,AGX-010 : 512, 640, 800, 1024, 1280, 1152, and 2048.


     When panning I occasionally get streaks if the virtual resolution
     is much greater than the physical resolution.  Moving the mouse a
     little makes it disappear. The Hercules manual indicates this also
     happens with the MS-Windows drivers.


     The server requires at least a 64KB scratchpad (16KB for XGA's).
     Additional memory is useful for font cache and a larger scratchpad.

     AGX Clocks:
        Probing is supported, but of course the usual warnings and
        disclaimers apply. Probing may momentarily subject your monitor
        to sweep frequencies in excess of its rating.  The cautious may
        wish to turn off the monitor while the probe is running.

        Once clocks are known, they can be entered into XF86Config, then
        subsequent runs won't probe clocks and will be quicker to
        startup. For the clock probe it is recommended that the X server
        be run with the -probeonly option. The values in the clocks
        statement are the hardware input clocks and correspond to the
        pixel clock only at 8bpp in direct-clocking RAMDAC modes. The
        server will divide/multiply those values as appropriate for the
        RAMDAC modes available at the current pixel depth. The available
        pixel clocks will be displayed in the startup messages.

        For the 2MB Hercules Graphites, with the "herc-dual-dac" RAMDAC
        specified, earlier versions of the server generated an
        additional 16 clocks with values doubled and some zeroed.  Those
        are no longer needed and you should re-probe and re-enter the
        clock values to ensure all clocks are available to you.

        The AGX-015 2MB Hercules Graphite VL Pro with an ICS1494M
        9251-516 clock chip has probed clock values of:

                       25.18  28.80  32.70  36.00  40.00  45.00  50.40  64.70
                       70.10  76.10  80.60  86.30  90.40  95.90 100.70 109.40


     Actual values according to Hercules are:

                    25.175 28.322 32.512 36.000 40.00 44.90 50.35 65.00
                    70.00  75.00  80.00  85.00  90.00 95.00 100.0 108.0


     These are the values to be used in the clock statement if specify-
     ing the "normal", "bt481", or "herc_small_dac" RAMDAC in your
     XF86Config and your clockchip matches that above.

     Clock probing assumes that the first clock is 25.175Mhz and uses
     that to derive the rest. A warning is displayed if the second is
     not near 28.322Mhz. If this warning appears, you should not use the
     probed clock values without additional verification from other
     sources.

     In the case of the AGX-014 and later AGX's, only the external clock
     select lines are used, this means the clock values correspond to
     the values of the video board's clock chip.

     For the AGX-010, the first 8 clocks use the standard XGA internal
     clock selects and the second 8 are based on AGX extensions. For the
     XGA-1 only 8 clocks are available.  The XGA-2 uses a programmable
     clock and no clocks or clockchip line is required.

     The maximum pixel clock generally allowed is 85MHz, but some
     RAMDACs support higher values. In any case you, should check your
     RAMDAC, some RAMDACs used on AGX based boards are produced in
     versions rated to lesser values than the server assumes. You should
     check the rating and limit yourself to that value.

     Modes:
        One difference I've noted from the Mach8, is that the AGX's CRTC

        doesn't like the start of the horizontal sync to be equal to
        horiz blank start (vert sync may have the same problem, I need
        to test some more). Interlaced and +/-sync flags are supported
        but have had very little testing. For interlaced modes make sure
        the number of lines is an odd number.

        The doublescan flag is now supported, however the minimum clock
        supported is generally 25MHz, so resolutions of less than
        400x300 are not likely to be supported by most monitors.  In
        creating doublescan mode timings, the vertical timings will
        match the apparent resolutions, e.g. for 400x300 the timings
        should describe 300 lines, not 600.

     Examples:
        For the Hercules HG720 (2MB VLB AGX-015, with BT481 and
        AT&T20C5050 RAMDACs), I use the following XF86Config "Device"
        section:

                     Section "Device"
                         Identifier "HG720"
                         VendorName "Hercules"
                         BoardName  "Graphite VL Pro"
                         Chipset    "AGX-015"
                         Clocks     25.2  28.3  32.5  36.0  40.0  45.0  50.4  65.0
                                    70.00  75.00  80.00  85.00  90.00 95.00 100.0 108.0
                         Videoram   2048
                         RamDac     "herc_dual_dac"
                         Option     "dac_8_bit"
                         Option     "no_wait_state"
                     EndSection


     For the Spider Black Widow Plus (2MB VLB AGX-016, with Sierra
     SC15021 RAMDAC):

                  Section "Device"
                      Identifier "SBWP"
                      VendorName "Spider"
                      BoardName  "Black Widow Plus"
                      Chipset    "AGX-016"
                      Clocks      25.2  28.3  39.9  72.2  50.0  76.9  36.1  44.8
                                  89.0  119.8 79.9  31.5 110.0  64.9  74.9  94.9
                      Videoram   2048
                      RamDac     "SC15025"
                      Option     "dac_8_bit"
                      Option     "no_wait_state"
                  EndSection



  6.  Xga configuration

  This server now has tested support for XGA-2 compatible boards (aka.
  XGA-NI). The main issue for XGA-1 support is whether clock probing
  works. At this time probing for board configuration is limited and
  detailed configuration may need to be done manually.

  By default the ISA POS register will be performed. If the XGA Instance
  number is specified the scope of probing will be narrowed a bit. To
  override or disable probing, a minimum of the Instance, COPbase, and
  MEMbase must be specified in the XF86Config device section for the XGA
  card. MCA probing is not supported.




     Instance       nn
        XGA instance number (0-7).

     IObase        nnnn
        The I/O address of the the XGA general control registers. The
        standard, and default, is 0x21i0, where i is the instance
        number.

     MEMbase        nnnn
        The XGA display memory address (the address the XGA coprocessor
        uses for video memory). This is also the system memory address
        of the linear aperture on boards that support it.

        POS register 4 bits 7-1 contains bits 31-25 of the XGA's display
        memory address. Bits 24-22 of of the display memory address
        contains the XGA instance number.  Bit 0 of POS register 4 is
        not used by this server as the XGA's linear aperture is not
        used.  However, the coprocessor must still be configured with
        this.

        The AGX-01[456] chips have a fixed display memory address.

     COPbase     nnnnnn
        Address of the graphics engine's memory mapped control
        registers.

        Typically:

        0xC1C00 + (ext_mem_addr * 0x2000) + (instance * 0x80)

        where ext_mem_addr is the high order 4-bits of POS register 2
        (0-16 the server assumes zero).

        The AGX-01[456] chips support 0xB1F00 (default) and 0xD1F00.

     BIOSbase     nnnnnn
        Address of the XGA BIOS (not VGA BIOS).  Can be specified as an
        alternate to COPbase.

        Typically:

        0xC0000 + (ext_mem_addr * 0x2000)

        where ext_mem_addr is the high order 4-bits of POS register 2
        (0-16 -- the server assumes zero).

     VGAbase        nnnn
        Can be used to override the default 0xA0000 address for the 64KB
        video memory address used by the server. The only values
        acceptable are 0xA0000 and 0xB0000. VGA text mode restore does
        not work under Linux if 0xB0000 is specified.

        AGX-01[456] also default to 0xA0000.

     POSbase       nnnn
        Can be used to specify an alternate POS register probe address
        base from the ISA default of 0x100. The VESA VXE standard for
        EISA is 0xzC80, where z is the slot number).

        A value of zero will disable POS register probing (required for
        MCA).

     DACspeed      nnnn
        Can be used to override the servers default maximum Pixel Clock
        for XGA-2 of 80Mhz.  The limit can be raised as high as 90Mhz,

        or set to lower values.

  An alternate way to determine the POS register values is with the
  setup/diag programs that should have been included with your video
  board, or possibly from jumper values.


  The XGA-2 has programmable clocks up to 90MHz, however at 1024x768,
  72MHz is generally the max that will produce a stable display with the
  CatsEye/XGA-2 used for testing (IBM coprocessor and INMOS
  RAMDAC/serializer). Higher clocks will often generate artifacts at the
  top and left edges of the screen. Such artifacts can sometimes be
  tuned out by increasing the vertical and horizontal blanking intervals
  or slightly changing the clock. At pixel clock rates above 80Mhz I
  have seen the chip lose sync after running for several minutes, so
  80Mhz has been set as the default limit for XGA-2 pixel clocks. I
  don't have specs on actual limits, and as there are a number of
  different XGA chipsets, you should use the modes documented in your
  owner's manual as a guide to max refresh rates. No clocks or clockchip
  parm are required to specify use of programmable clocks for the XGA-2.

  8bpp and 16bpp are supported for the XGA-2.

  For XGA-1 cards the clocks must be specified as for the AGX chips, it
  is not known whether the clockprobing will work. Some XGA-1 chips may
  support 16bpp.

  Generated from XFree86: xc/programs/Xserver/hw/xfree86/doc/sgml/agx.sgml,v 3.14 1995/12/28 03:49:35 dawes Exp $





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$XFree86: xc/programs/Xserver/hw/xfree86/doc/README.agx,v 3.28 1995/12/28 03:52:28 dawes Exp $
