> >Sounds cards are a good example of where `bounce buffers' are exactly
> >the wrong thing to do.  It means you can't ever mmap() the sound
> >buffer.
>
> Bounce-buffering is only needed by bus master cards, yes?  I've
> *never* seen a bus-mastering sound card.

Hm, not exactly, especially if you are in the "hair-splitting
mood" ;-)  It depends on what you call "bounce buffering": either
the variant NetBSD doesn't have at present (support for ISA
bus-master cards in machines with >16MB memory), or the more
generic function of limiting ISA DMA to the <16MB region.  From
my rummaging in the NetBSD internals a while ago, I seem to
remember that there is already bounce buffer support in for the
on-board DMA controller, and as you note all the currently
supported sound cards relies on the on-board DMA controller
(i.e. they are not ISA bus-master cards).

I agree that if we are to provide mmap capability for /dev/audio,
it's probably best to avoid that bouncing as well.

- Havard