opening control devices with "hw:N,M"

opening control devices with "hw:N,M"

[Paul Davis]

why doesn't this work:

    snd_ctl_open (&handle, "hw:0,0", ...)

it means that you can't use the same standard name format for control
devices as PCM devices, which is a bit of problem for programs that
need to open both but only want to require the user to specify a
single name ...

--p


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Re: opening control devices with "hw:N,M"

[Takashi Iwai]

At Thu, 18 Jul 2002 09:03:26 -0400,
Paul Davis wrote:
> 
> why doesn't this work:
> 
>     snd_ctl_open (&handle, "hw:0,0", ...)
> 
> it means that you can't use the same standard name format for control
> devices as PCM devices, which is a bit of problem for programs that
> need to open both but only want to require the user to specify a
> single name ...

do you suppose that the second argument of ctl name is always ignored?
the control interface has no device like pcm.

but it's true that having a same naming rule makes the life easier...


Takashi


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Re: opening control devices with "hw:N,M"

[Jaroslav Kysela]

On Fri, 19 Jul 2002, Takashi Iwai wrote:

> At Thu, 18 Jul 2002 09:03:26 -0400,
> Paul Davis wrote:
> > 
> > why doesn't this work:
> > 
> >     snd_ctl_open (&handle, "hw:0,0", ...)
> > 
> > it means that you can't use the same standard name format for control
> > devices as PCM devices, which is a bit of problem for programs that
> > need to open both but only want to require the user to specify a
> > single name ...
> 
> do you suppose that the second argument of ctl name is always ignored?
> the control interface has no device like pcm.
> 
> but it's true that having a same naming rule makes the life easier...

The 'default' is there for this purpose. Otherwise, application / user 
must know the right device name.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project  http://www.alsa-project.org
SuSE Linux    http://www.suse.com



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Re: opening control devices with "hw:N,M"

[Takashi Iwai]

At Sat, 20 Jul 2002 09:08:29 +0200 (CEST),
Jaroslav wrote:
> 
> On Fri, 19 Jul 2002, Takashi Iwai wrote:
> 
> > At Thu, 18 Jul 2002 09:03:26 -0400,
> > Paul Davis wrote:
> > > 
> > > why doesn't this work:
> > > 
> > >     snd_ctl_open (&handle, "hw:0,0", ...)
> > > 
> > > it means that you can't use the same standard name format for control
> > > devices as PCM devices, which is a bit of problem for programs that
> > > need to open both but only want to require the user to specify a
> > > single name ...
> > 
> > do you suppose that the second argument of ctl name is always ignored?
> > the control interface has no device like pcm.
> > 
> > but it's true that having a same naming rule makes the life easier...
> 
> The 'default' is there for this purpose. Otherwise, application / user 
> must know the right device name.

iirc, it's not easy to pass the card/device number to "default" pcm.
at least, "default:CARD=1" doesn't work.  the easiest way to access a
certain card is, so far, only to use "hw:x".
this must be fixed.

also, i thought that ctl.hw is defined purely in
/usr/share/alsa/alsa.conf, and tried to redefine this to accept more
arguments.  but it doesn't change anything.  is ctl.hw hardcoded?


Takashi


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Re: opening control devices with "hw:N,M"

[Jaroslav Kysela]

On Mon, 22 Jul 2002, Takashi Iwai wrote:

> At Sat, 20 Jul 2002 09:08:29 +0200 (CEST),
> Jaroslav wrote:
> > 
> > On Fri, 19 Jul 2002, Takashi Iwai wrote:
> > 
> > > At Thu, 18 Jul 2002 09:03:26 -0400,
> > > Paul Davis wrote:
> > > > 
> > > > why doesn't this work:
> > > > 
> > > >     snd_ctl_open (&handle, "hw:0,0", ...)
> > > > 
> > > > it means that you can't use the same standard name format for control
> > > > devices as PCM devices, which is a bit of problem for programs that
> > > > need to open both but only want to require the user to specify a
> > > > single name ...
> > > 
> > > do you suppose that the second argument of ctl name is always ignored?
> > > the control interface has no device like pcm.
> > > 
> > > but it's true that having a same naming rule makes the life easier...
> > 
> > The 'default' is there for this purpose. Otherwise, application / user 
> > must know the right device name.
> 
> iirc, it's not easy to pass the card/device number to "default" pcm.
> at least, "default:CARD=1" doesn't work.  the easiest way to access a
> certain card is, so far, only to use "hw:x".
> this must be fixed.

I don't agree here. The default is very simple case when the application 
programmer doesn't want to take care about the right syntax of the device 
specification.

Anyway, programmers should know that CTL devices are one per card. If 
there is some real need to correlate PCM handle with CTL handle, then we 
might create a special function like:

int snd_pcm_get_ctl_name(snd_pcm_t *handle, char **ctl_name);

> also, i thought that ctl.hw is defined purely in
> /usr/share/alsa/alsa.conf, and tried to redefine this to accept more
> arguments.  but it doesn't change anything.  is ctl.hw hardcoded?

Extra things in configuration file are usually parsed as errors.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project  http://www.alsa-project.org
SuSE Linux    http://www.suse.com




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Re: opening control devices with "hw:N,M"

[Takashi Iwai]

At Mon, 22 Jul 2002 21:21:47 +0200 (CEST),
Jaroslav wrote:
> 
> On Mon, 22 Jul 2002, Takashi Iwai wrote:
> 
> > At Sat, 20 Jul 2002 09:08:29 +0200 (CEST),
> > Jaroslav wrote:
> > > 
> > > On Fri, 19 Jul 2002, Takashi Iwai wrote:
> > > 
> > > > At Thu, 18 Jul 2002 09:03:26 -0400,
> > > > Paul Davis wrote:
> > > > > 
> > > > > why doesn't this work:
> > > > > 
> > > > >     snd_ctl_open (&handle, "hw:0,0", ...)
> > > > > 
> > > > > it means that you can't use the same standard name format for control
> > > > > devices as PCM devices, which is a bit of problem for programs that
> > > > > need to open both but only want to require the user to specify a
> > > > > single name ...
> > > > 
> > > > do you suppose that the second argument of ctl name is always ignored?
> > > > the control interface has no device like pcm.
> > > > 
> > > > but it's true that having a same naming rule makes the life easier...
> > > 
> > > The 'default' is there for this purpose. Otherwise, application / user 
> > > must know the right device name.
> > 
> > iirc, it's not easy to pass the card/device number to "default" pcm.
> > at least, "default:CARD=1" doesn't work.  the easiest way to access a
> > certain card is, so far, only to use "hw:x".
> > this must be fixed.
> 
> I don't agree here. The default is very simple case when the application 
> programmer doesn't want to take care about the right syntax of the device 
> specification.
 
ok.  so, you think that the default device is anyway exclusive,
which is not used for general type to multiple devices.

> Anyway, programmers should know that CTL devices are one per card. If 
> there is some real need to correlate PCM handle with CTL handle, then we 
> might create a special function like:
> 
> int snd_pcm_get_ctl_name(snd_pcm_t *handle, char **ctl_name);

it sounds not bad.
in the case of a multi pcm, it's not undetermined, though :)

btw, this reminds me another thing.
we have some controls which related with a certain pcm substream.
and so far we have no api to pass this relationship.

well, they are correlated via an index value.  yes, but confusingly, a
similar control can play a different role on the other driver.

perhaps by similar strategy, we may implement an api function for
that.

> 
> > also, i thought that ctl.hw is defined purely in
> > /usr/share/alsa/alsa.conf, and tried to redefine this to accept more
> > arguments.  but it doesn't change anything.  is ctl.hw hardcoded?
> 
> Extra things in configuration file are usually parsed as errors.

err, no, i meant that ctl.hw seems not to be read from the
configuration file...  most likely i made a stupid mistake.
don't take this serious yet.


ciao,

Takashi


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