From alsa-devel-owner@alsa.jcu.cz  Fri Mar 12 16:48:35 1999
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From: T.Mertes@mobilkom.at
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To: alsa-devel@alsa.jcu.cz
Subject: Enlarging the dma buffer for audiopci
Date: Fri, 12 Mar 1999 16:52:29 +0100
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Hello aggain

I forgot to mention:
I am not on the mailing list, please reply to
T.mertes@mobilkom.at


I have a SB 128 PCI sound card that i am using with
linux 2.2.3 and the ALSA sound driver "audiopci".

I have sound dropouts when playing wave files under load.
It comes from the fact that the program which plays
(sox, play, ...) has to wait sometimes (because of the
load) at the read() for too long. While the program waits, the
128kB buffer of the driver runs out and there is a dropout.

This seems to be really a buffer problem, because I have it
also with the sound driver from the kernel and with the
SB 16 vibra sound card.

I know that there are other ways to solve the problem.
(sound demon/playing program which use threads and
big buffers.) But I want first to investigate possibilitys to
repair the problem on the device driver side.

There are two possibilities here:

  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.

  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.

My question is:

  - Is it possible to enlarge the buffer of the audiopci driver
    to even several megabytes (configurabel like it is now).
  - Is there a built in ALSA or PCI-DMA limit which
    prohibits it? Can we lift this limit?
  - What is necessary to do to enlarge the buffer
    (a patch would be great :-) ).

I forgot to mention:
I am not on the mailing list, please reply to
T.mertes@mobilkom.at

Greetings Thomas


