[SDL] alsa and DMA..

Stephane Marchesin stephane.marchesin at wanadoo.fr
Mon Jan 31 15:28:54 PST 2005


Dave Airlie wrote:

>>>I see that the ALSA support in SDL doesn't use DMA, but read/write...
>>>
>>>I'm wondering has anyone thought about implementing DMA transfers for
>>>Alsa? or know if it would give much advantage.....
>>>
>>No idea if it would give a real speed advantage (probably not much). But
>>I do have plans to fix the alsa backend. I run the alsa kernel modules
>>at home (with oss emulation), and since the oss backend got broken from
>>the recent modifications (and alsa never quite worked) I'm stuck now.
>>Actually, I even think the SDL interface could map quite nicely to the
>>alsa dma stuff.
>>
>
>What problems are therre with the current alsa backend?
>
The problem seems specific to ac97 cards (I have one, and other ac97 
owners reported sound issues too), but I'm not sure.

> I was going to
>use it for my embedded app but I'm still waiting on a working
>development system with sound... I might get some time to look at this
>soon.... i.e. any CPU usage saving is a win for my current system (its
>getting a bit CPU starved...)
>

I'd say at most 3-4% cpu on a 500Mhz machine. I have not done such 
measurements for a long time, however so I can't say for a more recent cpu.

>
>>How old it the alsa dma api ? We have to keep backwards compatibility
>>with alsa < 1.0 too...
>>
>
>I think the dma api has been stable for a while.. but I'm not quite sure....
>
It'd be interesting to give it a try. I suspect it could fix the ac97 
problems as a side effect.

Well, ping me on irc or by mail if you do anything.

Stephane







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