Question on buffer size setting

Question on buffer size setting

[Allyn, Mark A]

Hello:
 
I am attempting to do some debugging of a new audio device, and I need
to change the
number of buffer descriptor list entries from the default of 16 to
something much
smaller, like 3.

I am a bit confused while looking at the code. There seems to be a value
labeled
SNDRV_PCM_HW_PARAM_BUFFER_SIZE, but I can't figure how it is set. Is
this a parameter that
is passed as part of the configure prior to doing a make for the driver?
Is this a parameter
passed to modprobe when loading the driver? 

Thanks for your help.

Mark

Re: Question on buffer size setting

[Takashi Iwai]

At Fri, 18 May 2007 18:00:18 -0700,
Allyn, Mark A wrote:
> 
> Hello:
>  
> I am attempting to do some debugging of a new audio device, and I need
> to change the
> number of buffer descriptor list entries from the default of 16 to
> something much
> smaller, like 3.

If you're referring to hda-intel, the number of buffer descriptor list
isn't fixed there.  The smallest size is 2 and the max size is 16.
(16 is used for allocation at the driver init time, though.)

> I am a bit confused while looking at the code. There seems to be a value
> labeled
> SNDRV_PCM_HW_PARAM_BUFFER_SIZE, but I can't figure how it is set. Is
> this a parameter that
> is passed as part of the configure prior to doing a make for the driver?
> Is this a parameter
> passed to modprobe when loading the driver? 

It's a parameter set by user-space at each time the application sets
up the PCM after opening the device.  The setup is done in hw_params
callback.


Takashi