Bug 15119

I am using Luigi's pcm snd code to drive my isa-pnp sound card.
I have previously used an el-cheapo opti933 but had the same problems
as I am now reporting and so plugged in a sb16-vibra.
Because it didn't work out at all, I have cvsupped my 3.3-stable from
09/26 today, rebuilt the kernel and got a little more success although
not for long.
Basically, the card either loops samples (the opti) or doesn't
output anything at all (on the sb-vibra, except for sometimes the
first chunk of dsp sample output).
The kernel logs the following:

timeout flushing dbuf_out, chan 5 cnt 0xff00 flags 0x000040c1
tsleep returns 4

which appears to me to be some kind of dma problem.
Interestingly sound worked for a short while after cvsupping
and building the new kernel but after I swapped the vibra
with the opti and back, I got the same problems as before.

I must note that at least the opti worked flawlessly with pcm
on freebsd 2.2.6 (except for an "ad1848 init failed" at boot
which however didn't affect functionality) so I don't think
it's only my hardware setup.