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<A HREF="tseng.html"><EM> Information for Tseng Chipset Users</EM></A>
 <b>:</b> <EM>Linear addressing and 16bpp/24bpp/32bpp modes </EM><BR>
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  <H2><A NAME="21"></A>14. Linear addressing and 16bpp/24bpp/32bpp modes </H2>

<p>Currently the 16-bit (32768 or 65536 colors), 24-bit (16M colors, packed
pixel), and 32-bit (16M colors, sparse) pixel support in the SVGA server
requires linear addressing. This restriction may be removed in a future
version, but with nearly all new cards using the PCI bus (where linear
addressing poses no problem), removing the linear addressing requirement
presently has a lower priority than other features. Option "linear" can be
specified in a depth-specific screen section to enable linear addressing; a
MemBase setting (in the device section) is probably also required on non-PCI
based systems, and optionally on PCI systems that have trouble finding out
for themselves where the MemBase is.</p>
<p>Non-PCI cards are not (or not well) supported in linear memory mode at this
moment. Some of them don't support it at all, and some of the ones that do
have so many address decoding bugs that it isn't feasible to provide a
working solution.</p>
<p>For the most part, many of the accelerated features in the 8bpp server have
been implemented to support 16, 24, and 32 bpp modes for the W32 and the
ET6000. So although there are now up to 4 times as many bits to display, the
X server shouldn't feel overly sluggish. Note also that the 24bpp and 32bpp
modes are only supported on a limited set of cards, and with at least 2Mb of
memory.</p>
<p>An ET6000 with 2.25 MB MDRAM is cheap-and-sound, since it can support exactly
1024x768 at 24bpp (using all available video memory). On all other video
cards, you need at least 4MB of video memory to do this. With only 2MB of
(M)DRAM, 960x720 is the best you can hope for.</p>
<p>In the <code>XF86Config</code> <code>"Screen"</code> section, a
<code>"Display"</code> subsection must be
defined for each depth that you want to run, with separate Modes
and virtual screen size. Example (2Mb of video memory):
<blockquote><code>
<pre>
Section "screen"
    SubSection "Display"
        Depth 8
        Virtual 1280 1024
        ViewPort 0 0
        Modes "640x480" "800x600" "1024x768"
    EndSubSection
    SubSection "Display"
        Depth 16
        Virtual 1024 992
        ViewPort 0 0
        Modes "640x480" "800x600" "1024x768"
    EndSubSection
    SubSection "Display"
        Depth 24
        Virtual 960 720
        ViewPort 0 0
        Modes "640x480" "800x600"
    EndSubSection
    SubSection "Display"
        Depth 32
        Virtual 832 600
        ViewPort 0 0
        Modes "640x480" "800x600"
    EndSubSection
EndSection
</pre>
</code></blockquote>
</p>

 <HR NOSHADE>
<A HREF="tseng.html"><EM> Information for Tseng Chipset Users</EM></A>
 <b>:</b> <EM>Linear addressing and 16bpp/24bpp/32bpp modes </EM><BR>
<b>Previous:</b> <A HREF="tseng13.html"><EM>ET6000 memory bandwidth hype and the impact on video modes </EM></A><BR>
<b>Next:</b> <A HREF="tseng15.html"><EM>Trouble shooting with the SVGA Tseng driver</EM></A>



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