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<TITLE>Cell Driver</TITLE>

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<H1>Mesa/Gallium Cell Driver</H1>

<p>
The Mesa
<a href="http://en.wikipedia.org/wiki/Cell_%28microprocessor%29" target="_parent">Cell</a>
driver is part of the 
<a href="http://www.tungstengraphics.com/wiki/index.php/Gallium3D" target="_parent">Gallium3D</a>
architecture.
</p>

<p>
<a href="http://www.tungstengraphics.com/" target="_parent">Tungsten Graphics</a>
is leading the project.
Two phases are planned.
First, to implement the framework for parallel rasterization using the Cell
SPEs, including texture mapping.
Second, to implement a full-featured OpenGL driver with support for GLSL, etc.
The second phase is now underway.
</p>


<H2>Source Code</H2>

<p>
The latest Cell driver source code is on the <code>gallium-0.2</code> branch
of the Mesa git repository.
After you've cloned the repository, check out the branch with:
</p>
<pre>
   git-checkout -b gallium-0.2 origin/gallium-0.2
</pre>
<p>
To build the driver you'll need the IBM Cell SDK (version 2.1 or 3.0).
To use the driver you'll need a Cell system, such as a PS3 running Linux,
or the Cell Simulator (untested, though).
</p>

<p>
If using Cell SDK 2.1, see the configs/linux-cell file for some
special changes.
</p>

<p>
To compile the code, run <code>make linux-cell</code>.
To build in debug mode, run <code>make linux-cell-debug</code>.
</p>

<p>
To use the library, make sure <code>LD_LIBRARY_PATH</code> points the Mesa/lib/
directory that contains <code>libGL.so</code>.
</p>

<p>
Verify that the Cell driver is being used by running <code>glxinfo</code>
and looking for:
<pre>
  OpenGL renderer string: Gallium 0.2, Cell on Xlib
</pre>


<H2>Driver Implementation Summary</H2>

<p>
Rasterization is parallelized across the SPUs in a tiled-based manner.
Batches of transformed triangles are sent to the SPUs (actually, pulled by from
main memory by the SPUs).
Each SPU loops over a set of 32x32-pixel screen tiles, rendering the triangles
into each tile.
Because of the limited SPU memory, framebuffer tiles are paged in/out of
SPU local store as needed.
Similarly, textures are tiled and brought into local store as needed.
</p>


<H2>Status</H2>

<p>
As of October 2008, the driver runs quite a few OpenGL demos.
Features that work include:
</p>
<ul>
<li>Point/line/triangle rendering, glDrawPixels
<li>2D, NPOT and cube texture maps with nearest/linear/mipmap filtering
<li>Dynamic SPU code generation for fragment shaders, but not complete
<li>Dynamic SPU code generation for fragment ops (blend, Z-test, etc), but not complete
<li>Dynamic PPU/PPC code generation for vertex shaders, but not complete
</ul>
<p>
Performance has recently improved with the addition of PPC code generation
for vertex shaders, but the code quality isn't too great yet.
</p>
<p>
Another bottleneck is SwapBuffers.  It may be the limiting factor for
many simple GL tests.
</p>


<H2>Debug Options</H2>

<p>
The CELL_DEBUG env var can be set to a comma-separated list of one or
more of the following debug options:
</p>
<ul>
<li><b>checker</b> - use a different background clear color for each SPU.
   This lets you see which SPU is rendering which screen tiles.
<li><b>sync</b> - wait/synchronize after each DMA transfer
<li><b>asm</b> - print generated SPU assembly code to stdout
<li><b>fragops</b> - emit fragment ops debug messages
<li><b>fragopfallback</b> - don't use codegen for fragment ops
<li><b>cmd</b> - print SPU commands as their received
<li><b>cache</b> - print texture cache statistics when program exits
</ul>
<p>
Note that some of these options may only work for linux-cell-debug builds.
</p>

<p>
If the GALLIUM_NOPPC env var is set, PPC code generation will not be used
and vertex shaders will be run with the TGSI interpreter.
</p>
<p>
If the GALLIUM_NOCELL env var is set, the softpipe driver will be used
intead of the Cell driver.
This is useful for comparison/validation.
</p>


<H2>Contributing</H2>

<p>
If you're interested in contributing to the effort, familiarize yourself
with the code, join the <a href="lists.html">mesa3d-dev mailing list</a>,
and describe what you'd like to do.
</p>


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