Example app source code or docs needed to help me do mmap.

Example app source code or docs needed to help me do mmap.

[James Courtier-Dutton]

Can someone point me to an example alsa app doing mmap ?

I want to convert my application from plain pcm_write  to mmap mode.
I would also like to understand how you detect if a sound card can do 
mmap or not.

I help develope a multimedia application, and 6 audio channels (5.1 
sound) starts to require mmap mode on very slow PCs.

Cheers
James

Re: Example app source code or docs needed to help me do mmap.

[Andy Wingo]

On Sat, 27 Apr 2002, James Courtier-Dutton wrote:

> Can someone point me to an example alsa app doing mmap ?

I like the implementation in jack's alsa_driver. It is tricky code
though (just MHO, after having ported it to a gstreamer alsa plugin) --
the write() api is of course much easier.

regards,

wingo.

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glue for new driver

[Guilhem Tardy]

Hi,

I am writing a driver for a new card, and wonder how the ALSA server will
recognize my module as one of its own? Besides, is there anything I should know
regarding debugging ALSA drivers?

Thanks,
Guilhem.


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Re: Example app source code or docs needed to help me do mmap.

[Paul Davis]

>Can someone point me to an example alsa app doing mmap ?
>
>I want to convert my application from plain pcm_write  to mmap mode.
>I would also like to understand how you detect if a sound card can do 
>mmap or not.
>
>I help develope a multimedia application, and 6 audio channels (5.1 
>sound) starts to require mmap mode on very slow PCs.

either

	aplay.c (simple, confusing)
	latency.c (simple, limited)
	{JACK}/alsa_driver.c (complete, confusing)

might help. I think that the Jack case is the only one that handles
what I would call "synchronous full duplex" (i.e. capture and playback
running in sync). the others don't tend to worry about that detail,
and it affects the inner loops of the code quite a bit.

to find out if mmap is support, you ask use

   snd_pcm_hw_params_set_access (handle, params,
			         SND_PCM_ACCESS_MMAP_NONINTERLEAVED);

or

   snd_pcm_hw_params_set_access (handle, params,
			         SND_PCM_ACCESS_MMAP_INTERLEAVED);

if it works, then it works :) BTW, any "plug" device supports mmap
mode regardless or not of the corresponding "hw" device(s) do. that's
partly why JACK uses mmap mode without checking for this - if a user
tries it on h/w that doesn't support it, they can just use
"plughw:D,S" instead of "hw:D,S" when naming it.

--p

Re: glue for new driver

[Paul Davis]

>Hi,
>
>I am writing a driver for a new card, and wonder how the ALSA server will
>recognize my module as one of its own? Besides, is there anything I should kno
>w
>regarding debugging ALSA drivers?

there is no "ALSA server", at least not in the context you're
discussing. 

you should download ALSA from CVS and build your driver within your copy
of the ALSA source tree, modifying makefiles etc. as needed to include
it in the build. that way, when its ready, you can submit a patch back
to jaroslav that includes everything thats needed, not just driver
source. 

--p