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Re: OLPC 'upstream'



Alan Cox wrote:
> On Thu, Feb 09, 2006 at 11:11:28AM +0000, Andy Green wrote:

>> That CPU has only 16K + 16K I/D cache.  The AT91RM9200 embedded chip I
>> use at the moment has the same cache :-O.  It does have 64-bit path to
>> its DRAM, but still, cache locality is going to be really critical.
> 
> 12K, 4K of the 16K D cache vanishes mysteriously as the blitter when in
> graphics mode. Also the RAM is shared with the video and although the video
> fetch is usually RLE encoded on that chip it still hurts, especially with
> funky shading and backgrounds.

Is that actually true for this "AMD Geode™ GX 500 1 0W" device variant?
 It says on p17 of the GX databook PDF that the GX1 type did have BLT
Buffers "In Cacahe Scratchpad RAM", but it says that for the GX500
variant being specified at the moment, BLT Buffers are "FIFOs in GP".
It also says above

''... The Graphics Processor is compatible with the graphics
processor used in the GX1 processor with additional functions
and features to improve performance and ease of
use. Like its predecessor, the Geode GX processor’s
Graphics Processor is a BitBLT/vector engine that supports
pattern generation, source expansion, pattern/source
transparency, and 256 ternary raster operations. New features
that have been added to the Graphics Processor
include:
• A 32-bit datapath that can support 32-bit ARGB full
color.
• Incorporated BLT FIFOs to replace the cache based
BLT buffers used in the GX1 processor.
• Improved bus protocols to increase bandwidth to the
memory controller.
• The ability to throttle BLTs according to video timing and
VGA hardware.

...''

If true that's good news, because losing the cache wouldn't help video
playback.

-Andy


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