[MPlayer-dev-eng] need help to port mpeg codecs to embeded devices on rockbox OS

[mirak]

Hello,

I am actually working on libmpeg2 for rockbox, the os for digital audio 
players like ipod and iriver.
The codec works actually, and we try to optimise it.

The difficulty is that this embeded devices have two type of RAM, the 
slow ram (sdram) and the fast ram (iram), so if all computations are 
done from slow ram it's slow because read and writes are slow, that's 
why the decoder structure is put in iram, to have the DCTblock computed 
very fast for exemple.

Iram is limited to 96K, and 45K is reserved for the codec.
Now the dificulty is to know which other part of the codec could use 
iram buffers to speed things up.
DCTblock is in IRAM it's only 128 bytes so it's not a problem, however 
it seems harder for motion compensation part to know what could be put 
in Iram, since a full image buffer is simply to big.
Some quantisations arrays and stuff are already stuffed in iram.

Maybe there could be buffers at macroblock level, we could work on the 
macroblock buffer in iram then swap data back to slow ram, but that's 
just an idea and I don't understand the code enough yet to figure this out.

Regards,

Mirak