XF86Config for STB Velocity 64VL

XF86Config for STB Velocity 64VL

Post by Kao L » Thu, 21 Mar 1996 04:00:00



Can some please help me config my video card for X11R6.  I have an
STB Velocity 64VL video card with 2MB dram.  The video card has an
S3 Vision 968 chip on it.  The monitor I'm using has horizontal scan
freq of 31.5-60 and vertical of 60-75 non-interlace.

Any help would be greatly appreciated.

kao

 
 
 

XF86Config for STB Velocity 64VL

Post by Don Dettk » Fri, 22 Mar 1996 04:00:00



>Can some please help me config my video card for X11R6.  I have an
>STB Velocity 64VL video card with 2MB dram.  The video card has an

                                       ^^^^
Are you sure about that? ---------------^^
I really don't think they ever put Dram on that model.

Quote:>S3 Vision 968 chip on it.  The monitor I'm using has horizontal scan
>freq of 31.5-60 and vertical of 60-75 non-interlace.

README.S3 told me everything I needed to know about setting up XFree86
for that card.  VideoModes.doc covers what you need to know to set up
modelines.  I thought it was a little verbose, though, so I put
together some notes on generating optimal modelines.  Hopefully
they will be helpful.  Of course, any time you play with video modes,
make sure you keep them within the specs of your monitor, or you could
"fry" it.

The thing you usually have to worry about is keeping your hsync rate within
the monitor's spec.  Also, keep vsync within the monitor's spec and keep
in mind that image quality may deteriorate if the Dot Clock Frequency (DCF)
exceeds the monitor's bandwidth rating.  If you enter the correct ranges for
your monitor in XF86Config, the server will protect you from straying
outside the monitor's range.

Here are some useful equations I gleaned/extrapolated from VideoModes.doc:

Here is a typical modeline:


Modeline "1152x864"    110    1152 1200 1392 1448   864  870  872  907
#                      DCF    HR   HG1  HG2  HFL    VR   VG1  VG2  VFL

Hsync = DCF / HFL
DCF = Hsync * HFL
RR = DCF / (VFL * HFL)

Where

BW    = BandWidth;  the maximum dot clock frequency the monitor can handle
            without sacrificing image quality.  This can be viewed as a soft
            guideline, while Hsync and Vsync (Refresh Rate) are hard limits.
Hsync = Horizontal Scan Frequency in KHz
Vsync = Vertical Scan Frequency in Hz, or Refresh Rate
DCF   = Dot Clock Frequency in MHz; should be <= monitor bandwidth

HR    = Horizontal Resolution (number of viewable dots/stripes in a row)
HFL   = Horizontal Frame Length (number of dots/stripes in a row, including
            those outside the viewable area); typically, HR + 20 to 30 percent
            (about 25% seems to work best for me).
            Increase this to make the image narrower, decrease it to make
            the image wider.
            IMPORTANT:  If you decrease this, you may have to decrease DCF
            as well, to keep Hsync within the monitor's specs!
HG1 & HG2 = Horizontal "Guards"; allows you to center the display
horizontally;
            a good starting point seems to be:  HG2 > HG1 and
            HG1 = HR + 32 and HG2 = HFL - 32

VR  = Vertical Resolution (number of viewable rows of dots)
VFL = Vertical Frame Length (number of rows, including those outside the
            viewable area); typically, VR + 2 to 7 percent
VG1 & VG2 = Vertical "Guards";  Allows you to center the display vertically;
            A good starting point here seems to be:
            VG1 and VG2 centered between VR and VFL and VG2 - VG1 = 8
RR  = Refresh Rate in Hz

Without a timing chart for the monitor, the "Guards" are really just a
guessing game.  If someone knows how to make better "best guesses" for
these, please share it.  Anyway, this should give xvidtune something to
work with.

To get the best refresh rate your monitor can handle at a given resolution:
- Calculate HFL for that resolution
- Calculate DCF, using the max Hsync your monitor can handle
- Fill in the rest of the modeline
- start X and use xvidtune to fine-tune the size and centering
     As you are doing this, keep an eye on the Horizontal sync to make
     sure you don't push it beyond what the monitor can handle.  If you
     "run into the wall", drop DCF a little and try again.
- put the new "tuned" values into the modeline

Please let me know if you have any observations or suggestions that
could help make these notes better.

--
Don Dettke,  Software Engineering Consultant