pcm hw parameters?

pcm hw parameters?

[Johannes Berg]

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Hi,

Quick question: When are the pcm hardware parameters surfaced to
userspace? Are those the ones I register in snd_pcm_new?

Thing is -- I have the problem that in theory, my codec can support
anything from 8KHz to 96KHz but when turning on digital output, it needs
to be restricted to the ones the digital output is ok with.

Of course I can trivially forbid turning on the digital out when a wrong
stream is open, but what about the other way around? When digital out is
turned on, and I forbid opening the stream when say 8KHz is selected,
does it screw over userspace and fail, or can I tell it what else to
use?

Similar things happen when you have digital input and it clocks both out
and in -- then you have to output the same bitrate as the input is
coming in at...

Thanks,
johannes

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Re: pcm hw parameters?

[Takashi Iwai]

At Fri, 24 Mar 2006 14:19:47 +0100,
Johannes Berg wrote:
> 
> Hi,
> 
> Quick question: When are the pcm hardware parameters surfaced to
> userspace? Are those the ones I register in snd_pcm_new?
> 
> Thing is -- I have the problem that in theory, my codec can support
> anything from 8KHz to 96KHz but when turning on digital output, it needs
> to be restricted to the ones the digital output is ok with.

It's hard to restrict parameters on demands (although theoretically
it's possible).  We usually provide two different devices, one for
the normal i/o and another for the digital i/o, to avoid such
conflicts.

The apps that send to the digital data would choose "spdif" or
whatever appropriate PCM name, and the system will reroute it.


Takashi


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Re: pcm hw parameters?

[Johannes Berg]

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On Mon, 2006-03-27 at 17:37 +0200, Takashi Iwai wrote:

> It's hard to restrict parameters on demands (although theoretically
> it's possible).  We usually provide two different devices, one for
> the normal i/o and another for the digital i/o, to avoid such
> conflicts.

I'm doing something like that now... Mind taking a look at i2sbus-pcm.c
in my git repo http://johannes.sipsolutions.net/snd-aoa.git/ ?

johannes

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