pcm buffer size

pcm buffer size

[Nicolas Hüppelshäuser]

Hi!

I'm using alsa 1.0.4.  How can I get a larger alsa buffer size?  The
maximum size returned by snd_pcm_hw_params_get_buffer_size_max is too
small.  I found no module option and nothing apropriate within the driver
code.  Mainly I'm using the snd-usb-audio module but others are also of
interest.

best regards
	Nicolas Hueppelshaeuser
--
nicolas hueppelshaeuser, emlix gmbh, http://www.emlix.com,
mailto:nh@emlix.com




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Re: pcm buffer size

[James Courtier-Dutton]

Nicolas Hüppelshäuser wrote:
> Hi!
> 
> I'm using alsa 1.0.4.  How can I get a larger alsa buffer size?  The
> maximum size returned by snd_pcm_hw_params_get_buffer_size_max is too
> small.  I found no module option and nothing apropriate within the driver
> code.  Mainly I'm using the snd-usb-audio module but others are also of
> interest.
> 
> best regards
> 	Nicolas Hueppelshaeuser
> --

You cannot. the value returned by 
snd_pcm_hw_params_get_buffer_size_max() is based on the hardware 
limitations. If you need more buffer space, buffer up the data in your 
application.

Cheers
James



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Re: pcm buffer size

[Clemens Ladisch]

Nicolas Hüppelshäuser wrote:
> I'm using alsa 1.0.4.  How can I get a larger alsa buffer size?

PCM devices have a default maximum buffer size and a maximum maxmimum
buffer size.  For example, in the snd-usb-audio driver, it's 64 KB and
128 KB.

The current value (in KB) can be seen in the file
/proc/asound/cardX/pcmXY/subX/prealloc.  You can change it with

  echo 128 > /proc/asound/card0/pcm0p/sub0/prealloc


In most cases, the maxmimum buffer size is constrained by hardware
limitations, but in the case of snd-usb-audio, it should be safe to
raise this value (look for the call to snd_pcm_lib_preallocate_pages()
in usbaudio.c).


HTH
Clemens





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