Re: [Alsa-devel] Re: [OT] ALSA userspace API complexity

John Rigg
2006-01-10T01:27:18Z

On Mon, Jan 09, 2006 at 04:29:45PM -0800, David Lang wrote:
> On Tue, 10 Jan 2006, John Rigg wrote:
>
> >>does the CPU touch the data for these, or do you DMA directly from
> >>userspace (i.e. "zero-copy")?
> >
> >The cards I mentioned use DMA. RME actually advertises that some of their
> >cards can handle 52 channels with zero CPU load. Their onboard DSPs can
> >also do routing and mixing, again without touching the CPU.
>
> I was under the (apparently mistaken) impression that you couldn't DMA
> from userspace (something to do with the possibility that the userspace
> memory pages could be swapped out in the middle of the DMA)

Hmm. Maybe I've been paying too much attention to card vendors'
sales talk :)

John