On Sun, 16 Sep 2001 11:59:53 -0700, Orion Hodson wrote:
> Maxim
> The sound driver interface provides the application writer the choice to set 
> the buffering they require.  This patch has obvious implications for the 
> ordering of ioctl's that we may not want to introduce.

Yes, OSS interface allows for that, but currently FreeBSD doesn't fully
provide applications with means to control buffering, because it only
allows application to regulate front buffer size and state, while retains
back buffer (i.e. DMA buffer) out of application's control, thus
significantly lowering its ability to control audio latency.

> I suspect (not insist :-) the two specific fixes you report are caused by:
>       - mss maximum buffer size is too small (4096 bytes ~ 23 ms of CD quality 
> audio).  Your patch helps because you increase the default buffering to 16384 
> bytes.
>       - digger relies on a sound library that does not always set the blocksize 
> (there are paths in the SDL audio code where this is the case, eg esd).  Your 
> patch helps because it sets the default buffer size smaller.

Not actually. If our pcm driver was correctly reporting its internal state
then SDL would be able to cope with situation intelligently (it has the code to
do so), but as long as now pcm driver doesn't reports to the application state
of its DMA buffers the application has no ways to regulate buffering
intelligently. You may want to look for my previous messages on topic (more
than a year ago on multimedia@ list). I reduced this problem by downsizing
a mss buffer size from the 64KB (sic!) to 4KB now, but this creates another
problem with the high speed audio. :((

> Increasing the default buffering is certainly an option we should consider.  
> However, any application that wants low latency should talk to the sound 
> device directly and use the existing ioctls to get this.  AFAIK, these work 
> very well, mail [EMAIL PROTECTED] if there are specific examples where this is 
> not the case.

See above.


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