libmad cache

Hi, i'm trying to run the code on a empeg player. 

All seems to work ok, but I need to modify the sources a bit and I have
to admit I don't fully (ok, mostly at all !) understand it.

What I need to do is get madlib to read a fixed size chunk of mp3 data,
then when playback is N seconds before the end of that chunk I want it
to read the next chunk.

IE I am trying read ahead to work round a problem with disk spin up time
on the device.

Strictly speaking the code does not need a cache, it can do the read
twice and throw the data from the first one away - all that matters is
that playback does not stop while the disk spins up, IE read of the real
data must never block :-)

I'm using a slightly modified madplayer at the moment linked against an
unmodified libmad.

Any advice?

Thanks,
Jon