From: Pedro Vasconcelos <pbv_at_st-andrews.ac.uk>
Date: Mon, 23 May 2005 00:06:46 +0100

Hello everyone,

I've joined the Rockbox devel list. I'm doing a PhD in computer science;
I have an ihp120 and a some experience in C and a little m68k assembly.
Never done any embedded sys or signal processing programming, though.

Anyway, the story so far: I've sucessfully instaled the rockbox in my
ihp, played with the configuration options (very nice), the playlist editor, the plugins.
Next I've setup the gcc cross compiler and rockbox sources.

Now I have been looking at what could be done to optimize the codecs,
particularly Vorbis because all my portable music is in this format.
Using vorbis2wav the unoptimzed Tremor is decoding at about 22% real
time. I did some profiling (on another machine-- a x86 laptop-- just to get a rough idea).
It seems like 20-40% of the decoding time is spent in mdct_backwards.

The only optimization I've been able to do is write some asm functions
to implement the 32x32 bit arithmetic using the Coldfire MAC
instructions. That improved playbay speed slightly to about 24-25%. The
other advantage is full 32 bit precision -- i.e. no need to use the
lower accuracy mode.

BTW, I also tested commmenting out mdct_backwards: playback improves to
40-45%, so clearly something else must be optimized...

I'm not sure how to proceed next-- any suggestions?

Pedro
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Received on 2005-05-23