snd_pcm_hw_params_current() ?

snd_pcm_hw_params_current() ?

[Florian Bomers]

Hi,

there is snd_pcm_sw_params_current() but not snd_pcm_hw_params_current(). How
can I get the current hardware configuration for a given snd_pcm_t handle ? Am I
missing something ?

Thanks,
Florian


-- 
Florian Bomers
Java Sound
Java Software/Sun Microsystems, Inc.
http://java.sun.com/products/java-media/sound/


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Re: snd_pcm_hw_params_current() ?

[Jaroslav Kysela]

On Thu, 3 Oct 2002, Florian Bomers wrote:

> Hi,
> 
> there is snd_pcm_sw_params_current() but not snd_pcm_hw_params_current(). How
> can I get the current hardware configuration for a given snd_pcm_t handle ? Am I
> missing something ?

Hardware parameters must be configured from application all time.

						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: snd_pcm_hw_params_current() ?

[Florian Bomers]

Jaroslav Kysela wrote:
> 
> On Thu, 3 Oct 2002, Florian Bomers wrote:
> 
> > Hi,
> >
> > there is snd_pcm_sw_params_current() but not snd_pcm_hw_params_current(). How
> > can I get the current hardware configuration for a given snd_pcm_t handle ? Am I
> > missing something ?
> 
> Hardware parameters must be configured from application all time.

So that means that I need to cache hw params if I ever want to use them again ?
E.g. my app does this:

open(), set hw params, set sw params
free hw params and sw params to save memory

work with the device: start/write/stop/etc.

When I now want to know the buffer size, I would like to obtain the current hw
params which I had set above to the pcm handle.

I understand that I initially need to set hw params to a pcm handle before I
could get current hw params, but once I did that, especially in prepared/running
state, the device has well-defined hw params and why shouldn't people be allowed
to query them ?

Thanks !
Florian

> 
>                                                 Jaroslav
> 
> -----
> Jaroslav Kysela <perex@suse.cz>
> Linux Kernel Sound Maintainer
> ALSA Project  http://www.alsa-project.org
> SuSE Linux    http://www.suse.com
> 
> -------------------------------------------------------
> This sf.net email is sponsored by:ThinkGeek
> Welcome to geek heaven.
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> _______________________________________________
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> Alsa-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/alsa-devel

-- 
Florian Bomers
Java Sound
Java Software/Sun Microsystems, Inc.
http://java.sun.com/products/java-media/sound/


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Re: snd_pcm_hw_params_current() ?

[Takashi Iwai]

At Fri, 04 Oct 2002 11:04:23 -0700,
Florian Bomers wrote:
> 
> Jaroslav Kysela wrote:
> > 
> > On Thu, 3 Oct 2002, Florian Bomers wrote:
> > 
> > > Hi,
> > >
> > > there is snd_pcm_sw_params_current() but not snd_pcm_hw_params_current(). How
> > > can I get the current hardware configuration for a given snd_pcm_t handle ? Am I
> > > missing something ?
> > 
> > Hardware parameters must be configured from application all time.
> 
> So that means that I need to cache hw params if I ever want to use them again ?
> E.g. my app does this:
> 
> open(), set hw params, set sw params
> free hw params and sw params to save memory
> 
> work with the device: start/write/stop/etc.
> 
> When I now want to know the buffer size, I would like to obtain the current hw
> params which I had set above to the pcm handle.
> 
> I understand that I initially need to set hw params to a pcm handle before I
> could get current hw params, but once I did that, especially in prepared/running
> state, the device has well-defined hw params and why shouldn't people be allowed
> to query them ?

simply because the query function is not implemented on the kernel
side :)

or, we can add the code to alsa-lib to duplicate the hw_params /
sw_params privately, and returns it via the query function.
but it's not much different fromt keeping hw_params or sw_params
record in the application by yourself.

please note that on the kernel, hw_params and sw_params are not stored
as they are but their members are copied to runtime struct.  so if the
query api is implemented, we need a function to convert from runtime
to hw_params or sw_params.


Takashi


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Re: snd_pcm_hw_params_current() ?

[Florian Bomers]

the thing that looks like bad API design is that snd_pcm_sw_params_current()
exists and snd_pcm_hw_params_current() does not. I think it wouldn't even hurt
if snd_pcm_hw_params_t would be cached in the lib for that. Maybe in a later
ALSA revision, ALSA kernel support for that could be implemented.

Thanks,
Florian

Takashi Iwai wrote:
> 
> At Fri, 04 Oct 2002 11:04:23 -0700,
> Florian Bomers wrote:
> >
> > Jaroslav Kysela wrote:
> > >
> > > On Thu, 3 Oct 2002, Florian Bomers wrote:
> > >
> > > > Hi,
> > > >
> > > > there is snd_pcm_sw_params_current() but not snd_pcm_hw_params_current(). How
> > > > can I get the current hardware configuration for a given snd_pcm_t handle ? Am I
> > > > missing something ?
> > >
> > > Hardware parameters must be configured from application all time.
> >
> > So that means that I need to cache hw params if I ever want to use them again ?
> > E.g. my app does this:
> >
> > open(), set hw params, set sw params
> > free hw params and sw params to save memory
> >
> > work with the device: start/write/stop/etc.
> >
> > When I now want to know the buffer size, I would like to obtain the current hw
> > params which I had set above to the pcm handle.
> >
> > I understand that I initially need to set hw params to a pcm handle before I
> > could get current hw params, but once I did that, especially in prepared/running
> > state, the device has well-defined hw params and why shouldn't people be allowed
> > to query them ?
> 
> simply because the query function is not implemented on the kernel
> side :)
> 
> or, we can add the code to alsa-lib to duplicate the hw_params /
> sw_params privately, and returns it via the query function.
> but it's not much different fromt keeping hw_params or sw_params
> record in the application by yourself.
> 
> please note that on the kernel, hw_params and sw_params are not stored
> as they are but their members are copied to runtime struct.  so if the
> query api is implemented, we need a function to convert from runtime
> to hw_params or sw_params.
> 
> Takashi
> 
> -------------------------------------------------------
> This sf.net email is sponsored by:ThinkGeek
> Welcome to geek heaven.
> http://thinkgeek.com/sf
> _______________________________________________
> Alsa-devel mailing list
> Alsa-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/alsa-devel

-- 
Florian Bomers
Java Sound
Java Software/Sun Microsystems, Inc.
http://java.sun.com/products/java-media/sound/


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