[theora-dev] [OT] Just saying hi!

Mike Melanson melanson at pcisys.net
Thu Feb 27 08:23:12 PST 2003

On Thu, 27 Feb 2003, Christoph Lampert wrote:

> ";-) The machines are fast enough anyway..." this may hold for users at
> home, but for anything slightly professional (generation of streaming
> material, broadcast clients) somehow I don't think many people will
> agree. Also, other plattforms might be more interesting than Joe User who
> downloads movies from the internet, e.g. portable devices etc. 

        One of the target applications I have in mind for this codec is a
Sega Dreamcast port. The DC has a 200 MHz Hitachi SH-4 CPU. I have no idea
how VP3 will perform but I am very eager to find out.

> Of course, prefetch would be essential. XVID (MPEG-4) works almost
> entirely in 16x16 blocks, all data except for motion estimation fits into
> L1-cache, so prefetch is not needed that often. But if the data to be
> processed is distributed over an area larger than L2 cache, and especially
> with large gaps, prefetch seems absolutely necessary. The problem is just
> that good prefetch depends very much on the underlying CPU, memory and
> it's speed... 

        I have suddenly become very conscious of cache and pre-fetching
issues. I found out the SH-4 has a whopping 16 kilobytes of data
cache...:) It does have a prefetch instruction capable of fetching 32 byte
blocks into the data cache. And the CPU manual listed no caveats about the
reliability of the instruction (I understand that Intel CPU prefetch
instructions are not guaranteed to do anything).

        Anyway, my primary focus is making it work, first. Then I'll think
about making it work fast.


	-Mike Melanson

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