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

John Rigg
2006-01-10T00:53:59Z

On Tue, Jan 10, 2006 at 12:16:17AM +0000, John Rigg wrote:
> On Mon, Jan 09, 2006 at 03:21:21PM -0800, David Lang 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.

Of course I should also mention that the sound cards deal with PCM audio
samples in integer format, but audio apps like jackd and its clients use
floating point, so in practice the CPU is still processing audio data much
of the time.

John