Re: snd_pcm_hw_params_current() ?

[Florian Bomers <Florian.Bomers@sun.com>]

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


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