Re: iBook and playing DVDs
On May 15 2002, Benjamin Herrenschmidt wrote:
> Whiwh seems silly. What should happen is
(...)
>
> That is you should have at least 2 buffers so you can asynchronously
> DMA a frame while decoding the next frame.
Yes, this queueing scheme was basically what I meant when I
wrote in an earlier message the following:
"And is the CPU stalled when the DMA transfer is being
performed? (...) If it is not, then even lowering the CPU
consumption would help, as there could be more processes
decoding the video, right?"
> It makes only sense to busy loop on the DMA if you are decoding
> faster than what you display. If this is not the case, then you are
> just throwing CPU cycles by the window.
And in the case of the G3 decoding video from a DVD, I learned
that every cycle is important, without any question, as it
doesn't feature vectorial instructions.
> The whole point of DMA is for the CPU to do something else while the
> ATI chip is doing the transfer.
Yes. According to mplayer's output, the r128 wastes quite a
lot of time in this iBook to output the video, even compared
to my Celeron 466 with a mach64 chip.
BTW, gentlemen, thank you for this quite instructive
discussion.
[]s, Roger...
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Rogério Brito - rbrito@iname.com - http://www.ime.usp.br/~rbrito/
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