Write Combining for PowerPC?
KendallB at scitechsoft.com
Sat Dec 11 08:23:06 EST 2004
We are working on some PowerPC machines and noticed that the boxes don't
appear to support the equivalent of Write Combining that we get on x86
boxes. Copies to Video Memory on our Motorola Sandpoint box run about
10Mb/s, which is terribly, terribly slow!
Does anyone know if it is possible to do something similar to Write
Combining for the PowerPC architecture, to speed up CPU access to the
linear framebuffer? Part of the problem is that for video overlay support
(not motion compensation) you have to dump the entire YUV frame into
video memory for the hardware overlay, and even on a 1GHz PPC box playing
an MPEG2 stream is not possible as X takes up over 80% of the CPU just to
copy the YUV data to video memory!
Obviously bus mastering will help solve this problem, but it would be
better if there was a way to enabling faster CPU access to the
framebuffer as well.
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