pcm transfer methods

pcm transfer methods

[Maarten de Boer]

i am going through the alsa-lib/test/pcm.c example, and i am
wondering about the different transfer methods available. are
there any guidelines or suggetions which method to use in 
which particular situation?

maarten



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Re: pcm transfer methods

[Takashi Iwai]

At Mon, 22 Jul 2002 10:38:52 +0200,
Maarten de Boer wrote:
> 
> i am going through the alsa-lib/test/pcm.c example, and i am
> wondering about the different transfer methods available. are
> there any guidelines or suggetions which method to use in 
> which particular situation?

please note the following is only my understanding:

for a serious audio use, mmap ("direct" in pcm.c) is the most
efficient method, if you can use it.
but it's not supported on every environment.
the mmap model is dependent on your card/pcm.
if the card supports non-interleaved only, then the mmap must be
non-interleaved, too.

"write" (and poll) is often easier for coding and for porting from/to
other OS.

"async" would be a choice if you cannot use (or don't want) threads
but want to process other things concurrently.
although there are some restrictions, in most cases this works fine.
the latency is not ensured like a thread scheduled with a high
priority, though.


Takashi


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driver's mixer interface

[Guilhem Tardy]

Hi all,

Could anyone tell me the purpose of the "index" field in struct snd_kcontrol_t
?

Thanks,
Guilhem.


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Re: driver's mixer interface

[Takashi Iwai]

At Mon, 18 Nov 2002 10:54:09 -0800 (PST),
Guilhem Tardy wrote:
> 
> Hi all,
> 
> Could anyone tell me the purpose of the "index" field in struct snd_kcontrol_t
> ?

if there are controls with the same name (e.g. a card with several
codec chips), they can be distinguished by different indices.


Takashi


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