gistfile1.txt

Yes. I've succeeded, except that I have a ADI dmc-2304 SVGA
monitor which supports only few clocks. I include parts of my
Xconfig here (unnecessary lines deleted to save bandwidth).
Behavior of these clocks is somehow strange: if I remove the
needless clock "31.5" won't X run any more in 800x600 resolution.

# The graphics drivers
# First the 8-bit colour SVGA driver
#
vga256

Chipset         "tvga8900c"
Clocks          25.2 28.3 31.5 35.5
# clocks supported by ADI dmc-2304
#Clocks         25.2 28.3 31.5 35.2 35.5 36.0
# clocks supported by Trident 8900c2.11
#Clocks         25.2 28.3 40.0 44.9 36.0 50.4 57.3 65.0 75.0
Screenno        0
Modes           "800x600" "640x480"
Videoram        1024
#ViewPort       0 0
Virtual         1152 900
#
# To disable SpeedUp, use NoSpeedUp
#NoSpeedUp

#
# Next the 1-bit mono SVGA driver
#
vga2

  Virtual       800 600
  ViewPort      0 0
#  Modes                "640x480"
  Modes        "800x600" "640x480"

# And last,  the database of video modes
#
ModeDB
# name        clock   horizontal timing     vertical timing      flags
 "640x480"     25      640  664  760  800    480  491  493  525

 "800x600"     36      800  824  896 1024    600  601  603  625