available sampling rate detection

available sampling rate detection

[Martin Herren]

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Hej,

i'm new on this list as well as to alsa.

We need to find out the supported sampling rates (and other parameters) for the pcm devices of soundcards.

We used snd_pcm_hw_params_test_rate() for this, which according to the documentation (http://www.alsa-project.org/alsa-doc/alsa-lib/group___p_c_m___h_w___params.html#a53)
should return 1 if the rate is available, 0 otherwise.
The problem is that it always returned an non-null value, for any rate even if we knew it wasn't supported.

Then we found out that we need to call snd_pcm_hw_params_any() first, and then snd_pcm_hw_params_test_rate() returns 0 for supported rates, and a negativ value (-22) otherwise.

Is this the correct way to do the test or did we miss a point ?
If it is correct, the documentation should be updated.

An additional question, what is the correct way to find out all existing cards/buses on a system ? Currently we scan /proc/asound/card?/ for all pcmX[cp]. Is there a better way to do it ?

Thanks,

Martin

-- 
Martin Herren

Protux - A Free Professional Audio Tool for GNU/Linux:
-> http://www.nongnu.org/protux/
Open your Windows - Free your Mind - Enjoy:
->http://gnuwin.epfl.ch



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Re: available sampling rate detection

[Takashi Iwai]

At Tue, 11 Feb 2003 08:53:59 +0100,
Martin Herren wrote:
> 
> Hej,
> 
> i'm new on this list as well as to alsa.
> 
> We need to find out the supported sampling rates (and other parameters) for the pcm devices of soundcards.
> 
> We used snd_pcm_hw_params_test_rate() for this, which according to the documentation (http://www.alsa-project.org/alsa-doc/alsa-lib/group___p_c_m___h_w___params.html#a53)
> should return 1 if the rate is available, 0 otherwise.
> The problem is that it always returned an non-null value, for any rate even if we knew it wasn't supported.
> 
> Then we found out that we need to call snd_pcm_hw_params_any() first, and then snd_pcm_hw_params_test_rate() returns 0 for supported rates, and a negativ value (-22) otherwise.

the documentation is wrong.  the test functions return zero if
supported and a negative value if not supported, as well as the set
functions do.


Takashi


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Re: available sampling rate detection

[Patrice Tisserand]

On Tue, 2003-02-11 at 08:53, Martin Herren wrote:
[..]
> An additional question, what is the correct way to find out all existing cards/buses on a system ? Currently we scan /proc/asound/card?/ for all pcmX[cp]. Is there a better way to do it ?
> 
I think you case use a loop with snd_card_next

from alsa-lib/src/control/card.c
 /**
 * \brief Try to determine the next card.
 * \param rcard pointer to card number
 * \result zero if success, otherwise a negative error code
 *
 * Tries to determine the next card from given card number.
 * If card number is -1, then the first available card is
 * returned. If the result card number is -1, no more cards
 * are available.
 */
int snd_card_next(int *rcard)  

-- 
Patrice Tisserand <Patrice.Tisserand@ircam.fr>
IRCAM



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Re: available sampling rate detection

[Martin Herren]

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On Tue, 11 Feb 2003 10:26:25 +0100
Patrice Tisserand <Patrice.Tisserand@ircam.fr> wrote:

> On Tue, 2003-02-11 at 08:53, Martin Herren wrote:
> [..]
> > An additional question, what is the correct way to find out all existing cards/buses on a system ? Currently we scan /proc/asound/card?/ for all pcmX[cp]. Is there a better way to do it ?
> > 
> I think you case use a loop with snd_card_next
> 
> from alsa-lib/src/control/card.c
>  /**
>  * \brief Try to determine the next card.
>  * \param rcard pointer to card number
>  * \result zero if success, otherwise a negative error code
>  *
>  * Tries to determine the next card from given card number.
>  * If card number is -1, then the first available card is
>  * returned. If the result card number is -1, no more cards
>  * are available.
>  */
> int snd_card_next(int *rcard)

thanks, i didn't have time to test it, but there seems to several interesting functions which could be what we need.

thanks to Takashi too... next time i'll try to read the source for such a question ;-)

/Martin

-- 
Martin Herren

Protux - A Free Professional Audio Tool for GNU/Linux:
-> http://www.nongnu.org/protux/
Open your Windows - Free your Mind - Enjoy:
->http://gnuwin.epfl.ch


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