g2 DMA

I am writing a Linux driver for sound on the Dreamcast (I wrote an
old-style OSS one, sans DMA, years ago, now I want a newer style ALSA
driver using DMA).

I wonder if there is anybody here with access to information about how
g2 DMA works? Information on the web has pretty much dried up lately and
the KOS developers even took g2 DMA out of their sources.

I seem to be able to get the basic DMA to work but have no dma_residue
function or similar.

The sources are at http://newgolddream.dyndns.info/repos

Thanks

Adrian