[pulseaudio-discuss] "Operation not permitted" and "ALSA woke us up to write new data ..."

[Daniel Mack]

Hi,

I'm currently trying to get PulseAudio to work with soundcards using the
snd-usb-caiaq driver and have some strange effects I would like to
share.

First thing is random occurance of "Operation not permitted" messages
from the pulseaudio daemon. I can - most of the time - connect using
'aplay -Dpulse', but Rhythmbox, for example, usually fails with this
message:

I: sink-input.c: Created input 1 "Playback Stream" on
   alsa_output.plughw_0_0 with sample spec s16le 2ch 44100Hz and
   channel map front-left,front-right
I: protocol-native.c: Requested tlength=200.00 ms, minreq=10.00 ms
I: protocol-native.c: Final latency 200.00 ms = 90.00 ms + 2*10.00 ms
   + 90.00 ms
I: module-alsa-sink.c: Trying resume...
E: module-alsa-sink.c: Failed to set hardware parameters: Operation
   not permitted

I use the terms 'random' and 'usually' because I couldn't really find
any pattern when that happens and what exactly it causes. As a matter of
fact, once the stream is started by aplay, Rhythmbox can connect as well
and submit data. If it can't (i.e., when the "Operation not permitted"
message occurs), Rhythmbox will freeze completely.


Another issue (that might - in contrast to the other one - be related to
my driver) is the following message which pulseaudio happens to spit out
regularily (most likely in bursts) after the stream start succeeded:

E: module-alsa-sink.c: ALSA woke us up to write new data to the device,
   but there was actually nothing to write! Most likely this is an ALSA
   driver bug. Please report this issue to the PulseAudio developers.

I'm not excluding a driver bug in general, but staring at my sources, I
don't know where it could specifically misbehave. The only information my
driver gives (and can give) is the current stream head, which the
alogrithm does correctly, I'm very sure. But if it was a general issue,
other sound cards would be equally affected.

Could anyone give me a hint of what's going wrong here? I'm going to ask
at alsa-devel as well, but wanted to sort out PA issues first.

Many thanks,
Daniel