Date: Mon, 03 Apr 2000 00:15:55 +0300 From: Maxim Sobolev <sobomax@altavista.net> To: freebsd-multimedia@freebsd.org Subject: Re: newpcm secondary dma buffer - why? Message-ID: <38E7B88A.CED012F3@altavista.net> References: <20000331220131.A95404@cons.org>
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Martin Cracauer wrote:
> Cameron, multimedia folks,
>
> could you explain why the newpcm driver uses a secondary buffer to
> collect data before it transmits it to the soundcard?
>
> struct _pcm_channel {
> [...]
> snd_dbuf buffer2nd;
> };
>
> Please don't say "it does buffering", I assume that :-) But so far
> I've been under the impression that such things are unneeded in
> today's soundcards and that it is extremly hard to get the mmap API to
> work with such a construction in between.
I agree. This also makes unfunctional convenient way to control sound
using select() or SNDCTL_DSP_GETOSPACE ioctl.
-Maxim
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