Linux Unleashed, Third Edition:Installing and Configuring XFree86





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Monitor Model
Setting the monitor properly is an important step in configuring XFree86, and one that is easy to mess up. If some of the settings are incorrect, damage can occur to the monitor, so take care! Patience and common sense will help, although the monitor’s operations manual is a much better source of information.

If you are unsure about any settings, select the most basic level until you can get more information. For example, if you’re not sure whether your monitor supports high resolutions, stick with VGA or SVGA until you can get confirmation.
The monitor section in the XF86Config file is broken into smaller subsections for convenience. We can look at the subsections in a little more detail. The first section asks for information about the monitor type and model number. This subsection looks like this:


Section “Monitor”

Identifier “Generic Monitor”
VendorName “Unknown”
ModelName “Unknown”


The entries in this section are text strings only and have no real configuration value for XFree86. The only time they are used is when the text strings are echoed back to you when XFree86 starts up or a utility displays configuration information. You can enter the proper values for these items to make XFree86 a little more friendly to work with.

The next subsection deals with the horizontal bandwidth of the monitor. This is an important section, and you should try to find the actual values for your monitor. Some settings for specific brands are listed in the documentation accompanying XFree86, especially in the documents Monitors and VideoModes.doc. Check your distribution directories for any specification document files. If you can’t find specific values for these settings, use the lowest setting as a default, unless you know your monitor is capable of higher values. The bandwidth section looks like this:


# Bandwidth is in MHz unless units are specified

Bandwidth 25.2

# HorizSync is in kHz unless units are specified.
# HorizSync may be a comma separated list of discrete values, or a
# comma separated list of ranges of values.
# NOTE: THE VALUES HERE ARE EXAMPLES ONLY. REFER TO YOUR MONITOR’S
# USER MANUAL FOR THE CORRECT NUMBERS.

HorizSync 31.5 # typical for a single frequency fixed-sync monitor

# HorizSync 30-64 # multisync
# HorizSync 31.5, 35.2 # multiple fixed sync frequencies
# HorizSync
15-25, 30-50 # multiple ranges of sync frequencies


The bandwidth settings have good comments next to them, as shown in the preceding code. If you were installing a multisync monitor, for example, you could comment out the 31.5K Hz line and uncomment the 30-64 KHz line.

The vertical refresh rate is set in another subsection and is as critical to your monitor’s good health as the bandwidth. Again, check the documentation for more information. The vertical refresh subsection code looks like this:


# VertRefresh is in Hz unless units are specified.
# VertRefresh may be a comma separated list of discrete values, or a
# comma separated list of ranges of values.
# NOTE: THE VALUES HERE ARE EXAMPLES ONLY. REFER TO YOUR MONITOR’S
# USER MANUAL FOR THE CORRECT NUMBERS.
VertRefresh 60 # typical for a single frequency fixed-sync monitor

# VertRefresh 50-100 # multisync
# VertRefresh 60, 65 # multiple fixed sync frequencies
# VertRefresh 40-50, 80-100 # multiple ranges of sync frequencies


The comments in the file help out again, showing you the most common settings. These can be used as a guide but you should check your documentation for specifics.

Setting the video modes correctly is very important, as too high a video resolution may cause snow, a blank screen, or a system crash. The SuperProbe utility discussed earlier can help determine supported video modes, although most monitors have a good list of supported modes in their documentation. The XFree86 Monitors file also lists many popular monitors and their modes. The subsection for setting the video modes is as follows:


# Modes can be specified in two formats. A compact one-line format, or
# a multi-line format.

# A generic VGA 640x480 mode (hsync = 31.5kHz, refresh = 60Hz)
# These two are equivalent

# ModeLine “640x480” 25.175 640 664 760 800 480 491 493 525

Mode “640x480”
DotClock 25.175
HTimings 640 664 760 800
VTimings 480 491 493 525
EndMode

# These two are equivalent

# ModeLine “1024x768i” 45 1024 1048 1208 1264 768 776 784 817 Interlace

Mode “1024x768i”
DotClock 45
HTimings 1024 1048 1208 1264
VTimings 768 776 784 817
Flags “Interlace”
EndMode


The preceding examples show a standard VGA (640×480) resolution and a high (1,024×768) resolution. You can modify these entries to match your specific resolution requirements. As you can see from the preceding code, you need to know the dot clock and horizontal and vertical timings for your monitor and video card. Check the documentation! Note that you can specify all the details for the modes on a single line, but the more verbose listings are easier to read and work with.




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