Re: DMA past and present

Alan Cox (alan@cymru.net)
Mon, 17 Jun 1996 09:08:39 +0100 (BST)

> As far as I know, linux-doom's soundserver uses 16bit DMA normally, and
> I've also have such problems when trying to do 16bit WAV-playback with
> my AHA-1542. I think there are some difficulties with two 16bit DMA
> transfers at the same time, but I don't know the exact source of it.
>
> Does someone know more?

The ISA bus can only do one DMA transfer at a time. This means long slow
transfers (like sound) can cause other devices to time out. We have a
similar non sound example here. Streaming from an AHA1542 scsi disk to
QIC02 tape causes the ethernet controller (DMA driven also - lance) to
drop packets erratically as it cannot get enough DMA bandwidth itself.

Its normally sound+something which shows it up, but its not a sound issue
directly.

Alan