Re: snd_pcm_hw_params_current() ?

[Takashi Iwai <tiwai@suse.de>]

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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