Another thing that goes wrong is that the card cannot cope with the screen depth of 24 bit when running dual screen. This is probably a memory issue. Make sure you allow for it to drop to 16bit (or lower with older equipment).
This means having these options included in the screens sections of the xorg.conf.
For those who have asked here's my xorg.conf:
Code:
##########################################################################################
# /etc/X11/xorg.conf (xorg X Window System server configuration file)
#
# This version by: Kerry Mayes, February 2007.
# For Dell Latitude D520 with external Viewsonic VE710b Monitor connected via docking station.
#
# As an edited file, it will not be automatically updated on xserver-xorg package upgrades.
#
# I have not run the following command to allow it to be automatically updated:
# sudo dpkg-reconfigure -phigh xserver-xorg
#
# Updated by: Kerry Mayes, May 2007 for Feisty changes
# Xinerama no longer used as xorg now runs a session for each monitor.
##########################################################################################
#
# These sections have not been altered except to update for Feisty
Section "Files"
FontPath "/usr/share/fonts/X11/misc"
FontPath "/usr/share/fonts/X11/cyrillic"
FontPath "/usr/share/fonts/X11/100dpi/:unscaled"
FontPath "/usr/share/fonts/X11/75dpi/:unscaled"
FontPath "/usr/share/fonts/X11/Type1"
FontPath "/usr/share/fonts/X11/100dpi"
FontPath "/usr/share/fonts/X11/75dpi"
# path to defoma fonts
FontPath "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
EndSection
Section "Module"
Load "bitmap"
Load "ddc"
Load "dri"
Load "extmod"
Load "freetype"
Load "glx"
Load "int10"
Load "type1"
Load "vbe"
EndSection
Section "InputDevice"
Identifier "Generic Keyboard"
Driver "kbd"
Option "CoreKeyboard"
Option "XkbRules" "xorg"
Option "XkbModel" "pc104"
Option "XkbLayout" "us"
Option "XkbOptions" "lv3:ralt_switch"
EndSection
Section "InputDevice"
Identifier "Configured Mouse"
Driver "mouse"
Option "CorePointer"
Option "Device" "/dev/input/mice"
Option "Protocol" "ImPS/2"
Option "ZAxisMapping" "4 5"
EndSection
Section "InputDevice"
Identifier "Synaptics Touchpad"
Driver "synaptics"
Option "SendCoreEvents" "true"
Option "Device" "/dev/psaux"
Option "Protocol" "auto-dev"
Option "HorizScrollDelta" "0"
EndSection
#
##########################################################################################
#
# First device section, will control the Laptop LCD screen
Section "Device"
Identifier "D520 945GM 0"
Driver "i810"
BusID "PCI:0:2:0"
# This next line is required for xinerama.
Screen 0
# It was stated somewhere that the LFP is always the second pipe. Make sure never
# to have a space after the "," it's interpreted as "None".
Option "MonitorLayout" "CRT,LFP"
# I don't think these next lines are actually required.
Option "BackingStore" "true"
Option "DevicePresence" "on"
Option "DisplayInfo" "FALSE"
Option "DRI" "true"
Option "CacheLines" "1024"
EndSection
#
##########################################################################################
#
# Second device section, will control the external screen
Section "Device"
Identifier "D520 945GM 1"
Driver "i810"
# Even though there is a second pci address for the card, only this one is used for
# the external monitor. The other may be for the svideo out but that has not been
# confirmed.
BusID "PCI:0:2:0"
# This next line is required for xinerama.
Screen 1
# It was stated somewhere that the LFP is always the second pipe. Make sure never
# to have a space after the "," it's interpreted as "None".
Option "MonitorLayout" "CRT,LFP"
# I don't think these next lines are actually required.
Option "BackingStore" "true"
Option "DevicePresence" "on"
Option "DisplayInfo" "FALSE"
Option "DRI" "true"
Option "CacheLines" "1024"
EndSection
#
##########################################################################################
#
# First Monitor section, for the Laptop LCD screen.
Section "Monitor"
Identifier "D520 Monitor"
# I can't find a definitive source for these values, but these are the ones Fiesty came up with.
HorizSync 28-70
VertRefresh 43-60
DisplaySize 304 228 # From manual
Option "DPMS"
EndSection
#
##########################################################################################
#
# Second Monitor section, for the Viewsonic monitor connected to the docking station.
Section "Monitor"
Identifier "Viewsonic VE710b Monitor"
# These values are from the monitor's manual.
HorizSync 30-82
VertRefresh 50-75
DisplaySize 338 270
Option "DPMS"
EndSection
#
##########################################################################################
#
# First screen section, connects the first device to the Laptop LCD screen.
# Note that the resolution "1400x1050" wasn't available until I had installed 915resolution
Section "Screen"
Identifier "D520 Screen"
Device "D520 945GM 0"
Monitor "D520 Monitor"
DefaultDepth 24
SubSection "Display"
Depth 24
Modes "1400x1050" "1280x1024" "1024x768"
viewport 0 0
EndSubSection
SubSection "Display"
Depth 16
Modes "1400x1050" "1280x1024" "1024x768"
viewport 0 0
EndSubSection
EndSection
#
##########################################################################################
#
# Second screen section, connects the second device to the Viewsonic monitor connected to
# the docking station.
Section "Screen"
Identifier "Viewsonic VE710b Screen"
Device "D520 945GM 1"
Monitor "Viewsonic VE710b Monitor"
DefaultDepth 24
SubSection "Display"
Depth 24
Modes "1280x1024" "1024x768"
# This next line has been found useful when xinerama automatically makes
# the two screens the same virtual size - this command can be used on the
# lower resolution screen to limit it to the resolution it can display
# without scrolling.
# virtual 1280 1024
viewport 0 0
EndSubSection
SubSection "Display"
Depth 16
Modes "1280x1024" "1024x768"
# This next line has been found useful when xinerama automatically makes
# the two screens the same virtual size - this command can be used on the
# lower resolution screen to limit it to the resolution it can display
# without scrolling.
# virtual 1280 1024
viewport 0 0
EndSubSection
EndSection
#
##########################################################################################
#
# The serverlayout section to put it all together.
# Currently I use this file for both Laptop only and Dual screens so have to comment things
# out or put them back in each time I switch.
#
Section "ServerLayout"
Identifier "Default Layout"
# For the Intel, having a screen number in these lines seems to get it confused.
Screen "D520 Screen" 0 0
# Comment out the next two lines to use just the laptop screen.
Screen "Viewsonic VE710b Screen" LeftOf "D520 Screen"
# Option "Xinerama" "on"
Option "Clone" "off"
InputDevice "Generic Keyboard"
InputDevice "Configured Mouse"
InputDevice "Synaptics Touchpad"
EndSection
#
# Sometimes gnome remembers layout stuff that screws up the screen - you can't drag windows
# into certain parts of the screen and so forth. The solution I found on the forums was to
# delete the following directory: [home directory]/.gconf/desktop/gnome/screen
#
#
##########################################################################################
#
# These sections not altered.
Section "ServerFlags"
EndSection
Section "DRI"
Mode 0666
EndSection
#
##########################################################################################
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