On Sat, 5 Feb 2000, Michael R. Zucca wrote:
> I think I remember one unusal thing about the DMA engine is that it doesn't
> have a request FIFO. It just has two registers and you have to sort of flop
> back and forth between them. I could be thinking of something else, though.

Yeah, that's pretty much it :) Each DMA channel has two sets of
registers associated with it. When you get the DMA completion interrupt,
you switch over to the other register set and start another transaction
on that set. Or something like that... it's been years since I actually
looked at the code :)

BTW, something I think would be good to do before writing more DMA
drivers is to implement the bus_dma(9) interface and switch the ethernet
driver over to that... I don't know if we've got enough info on the Mac
hardware to do it though.