Linux Unleashed, Third Edition:Installing and Configuring XFree86





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Video Cards
The next subsection of the XF86Config file deals with the video card your system uses. You can have several cards defined with different resolutions, or simply enter the one that you will use the most. For example, the following subsection has a VGA and SVGA generic driver defined:


Section “Device”
Identifier “Generic VGA”
VendorName “Unknown”
BoardName “Unknown”
Chipset “generic”
VideoRam 256
Clocks 25.2 28.3
EndSection

Section “Device”
# SVGA server auto-detected chipset
Identifier “Generic SVGA”
VendorName “Unknown”
BoardName “Unknown”
EndSection


The Identifier, VendorName, BoardName, and optional Chipset entries are strings and are used only for identification purposes. The VideoRam (the amount of RAM on the video board) and Clocks entries are used to specify any particular behavior for your card. These should be carefully checked to verify the information, as illegal entries can cause damage to some video boards.
If you have a particular video board that has special features, you can create a Device entry for that board. For example, the following entry is used for a Trident TVGA board:


Section “Device”
Identifier “Any Trident TVGA 9000”
VendorName “Trident”
BoardName “TVGA 9000”
Chipset “tvga9000”
VideoRam 512
Clocks 25 28 45 36 57 65 50 40 25 28 0 45 72 77 80 75
EndSection


The information in the VideoRam and Clocks lines is taken from the documentation file that accompanies XFree86, although it can be entered manually from the video card’s documentation.
Some video boards require more detail, provided by additional entries in the devices subsection. For example, the following is for an Actix GE32+ video card with 2MB of RAM on board:


Section “Device”
Identifier “Actix GE32+ 2MB”
VendorName “Actix”
BoardName “GE32+”
Ramdac “ATT20C490”
Dacspeed 110
Option “dac_8_bit”
Clocks 25.0 28.0 40.0 0.0 50.0 77.0 36.0 45.0
Clocks 130.0 120.0 80.0 31.0 110.0 65.0 75.0 94.0
EndSection


You will see that the Ramdac and Dacspeed options, as well as an Option line, have been added to the entry. The entries that are allowed in this subsection change with each release of XFree86, so check the man pages or documentation files for more details if you want to get the most out of your video card.
The XFree86 Server
Earlier in this chapter, we looked at the XFree86 server and showed how you should choose one for your X server specifically. The server section of the Xconfig or XF86Config file is where the server specification is located. The server subsection from an XF86Config file looks like this:


Section “Screen”
Driver “svga”
Device “Generic SVGA”
Monitor “Generic Monitor”
Subsection “Display”
Depth 8
Modes “640x480”
ViewPort 0 0
Virtual 800 600
EndSubsection
EndSection


The preceding section shows a generic SVGA driver. The card supports the VGA 640×480 and SVGA 800×600 resolutions. If you have a more powerful video card and monitor combination, you can use a specific server file if it exists, such as the driver for the Actix GE32+ card with 2MB RAM, shown as follows:



Section “Screen”
Driver “accel”
Device “Actix GE32+ 2MB”
Monitor “Generic Monitor”
Subsection “Display”
Depth 8
Modes “640x480”
ViewPort 0 0
Virtual 1280 1024
EndSubsection
SubSection “Display”
Depth 16
Weight 565
Modes “640x480”
ViewPort 0 0
Virtual 1024 768
EndSubsection
EndSection


This card is set to use the special accelerated server file for the Actix card, supporting up to 1,280×1,024 resolutions. Check the list of servers to see whether there is one specifically designed for your video card. If you are not sure, default to a generic driver!

The options in this subsection do not apply to all cards, but you can set their values if you know them. The most important (and most often used) options are as follows:

•  Depth: the number of color planes (the number of bits per pixel). Usually the depth is 8, although VGA16 servers have a depth of 4 and monochrome displays have a depth of 1. Accelerated video cards can have depths of 16, 24, 32, or even 64 bits per pixel, usually indicated as part of the model name (for example, the Diamond Stealth 24 card has a pixel depth of 24, although check before you assume the card’s model name really is the depth!).
•  Modes: a list of the video mode names defined in the ModeLine option in the Monitor section. This shows all the modes the card supports and that you want to use. The first mode on the list is the default value when XFree86 starts. You can then switch between the other modes when XFree86 is running.
•  Virtual: the virtual desktop size. With extra RAM on the video card, you can have a virtual desktop larger than the screen display, and can then scroll around the virtual desktop with the mouse. You can, for example, have a virtual desktop of 1,024×768 but display only 800×600 (SVGA). The support for different virtual desktop sizes depends on the amount of RAM and the depth you use. For example, 1MB of RAM on the video card supports 1,024×768 with a depth of 8.2MB RAM supports the same size with a depth of 16 or a 1,280×1,024 desktop at a depth of 8. To use a true virtual desktop, use the fvwm window manager (usually used by default).
•  ViewPort: used with the virtual desktop to define the coordinates of the upper-left corner of the virtual desktop when XFree86 starts.





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