[nas] Re: Sound dropouts using ALSA and NAS on Linux

David Morano morano at computer.org
Thu Aug 24 19:14:33 MDT 2000

Jon wrote :

> Note, I got the same dropouts whether I was using NAS or doing the
> hw directly.  

Ya, you have a HW card or HW driver problem rather than anything in NAS.
If you cannot play something directly to your HW without problems
then NAS certainly cannot be expected to be any better !

My problem is that anything sent to the HW directly always plays just
fine.  No problems at all, which is why Sun is probably totally content
with their existing audio drivers (for better or for worse).  Only when
I play the exact same thing through the NAS server daemon does the
sound break up (drop-outs).  The funny thing is that the sound breaks
up more on the faster Sun Ultra SPARC box than on an old slower
Sparc-20 box.  This does seem to indicate that the problem may indeed
be with SIGPOLL coming late on the Ultra (running Solaris 2.6) for some
reason.  There are two different drivers used on the two different
boxes, which would also indicate the difference in getting SIGPOLL
raised as soon as it is supposed to be.

I think that a final solution will have to be either a separate thread
in the NASD program for issuing blocking writes, or by using some
'aiowrite(3)' or 'aio_write(3R)' calls (as Charles Levert suggested).
(Oh, by the way, Charles, that seems like an excellent idea !)  Either
way, I think the Sun HW might have to have writes waiting on the queue
all of the time in order to avoid dropouts.

This sort of NASD program design (not using SIGPOLL or other signals)
might be the best way to program all HW (not just Suns) in the end.
Other OSes might be slow in getting SIGPOLL raised also, maybe.

Dave Morano
morano at computer.org

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