From alsa-devel-owner@alsa.jcu.cz  Fri Mar 12 17:11:53 1999
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Date: Fri, 12 Mar 1999 17:11:38 +0100 (MET)
From: Andy Lo A Foe <arloafoe@cs.vu.nl>
To: alsa-devel@alsa.jcu.cz
Subject: Re: Enlarging the dma buffer for audiopci
In-Reply-To: <48A7CB4095A7D11187EF00609748374C02F161AF@w1sxms01.mobilkom.at>
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On Fri, 12 Mar 1999 T.Mertes@mobilkom.at wrote:

>   1. The sound driver does not use its 128kB efficient
>       (After issuing a write() the buffer should always be
>       almost full). I do not think that this is the case,
>       but I would be happy if the driver writer would check
>       this also.

This is something that should be controlled by the user program really.

>   2. A buffer of 128kB is too small (I think this is the case).
>       I would like to enlarge the buffer (I have to try out,
>       which buffer size is necessary). The current audiopci
>       driver limits the size of the dma buffer to at most 128k.

Why would you want to do such large buffering in the kernel? 


> My question is:
> 
>   - Is it possible to enlarge the buffer of the audiopci driver
>     to even several megabytes (configurabel like it is now).

Maybe, but not practical. Many programs can do flawless playback with very
small DMA buffers even. The trick is to do smart buffering and/or set the
program/thread that's feeding the audio card at a higher priority (RT) to
prevent underruns (skipping). 

>   - Is there a built in ALSA or PCI-DMA limit which
>     prohibits it? Can we lift this limit?

It could be difficult to allocate large amounts of contigeous buffers in
the lower 16MB memory range.

>   - What is necessary to do to enlarge the buffer
>     (a patch would be great :-) ).

Patch the user programs ;-)

Andy
--
Andy Lo A Foe, arloafoe@cs.vu.nl |   Linux v2.2.2   | PII 266 
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