28 Jan
2013
28 Jan
'13
11:19 p.m.
Hello,
I'm trying to poll mixer events in Alsa using C. I've used the following
functions within an infinite while loop:
if (snd_hctl_wait(hctl,-1))
{
...
}
###### and
snd_hctl_poll_descriptors(hctl, poll_fds, 1);
err = poll (poll_fds, 1, -1);
if (poll_fds[0].revents & POLLIN)
{
...
}
While I can get the first mixer event fine, in all subsequent rounds,
both snd_hctl_wait and poll always return immediately.
With the snd_mixer functions one has to call snd_mixer_handle_events to
clear events. However, calling snd_hctl_handle_events here never returns
and I can't quite figure out why. Nonetheless, I'm not even sure that's
the key to my solution.
Can anyone give me some advice on how to get this working?
Kind regards, Maarten
29 Jan
29 Jan
12:57 a.m.
New subject: Alsa: poll mixer events, always returns true in subsequent calls
On Mon, Jan 28, 2013 at 11:19:00PM +0100, Muffinman wrote:
While I can get the first mixer event fine, in all
subsequent rounds,
both snd_hctl_wait and poll always return immediately.
With the snd_mixer functions one has to call snd_mixer_handle_events to
clear events. However, calling snd_hctl_handle_events here never returns
and I can't quite figure out why. Nonetheless, I'm not even sure that's
the key to my solution.
Can anyone give me some advice on how to get this working?
Can't help, just offer my sympathy... Having been there just a few
hours ago, to me its seems that trying to program for ALSA using
the available (doxygen) documentation is like trying to learn a
new natural language from a dictionary for that language only -
without any grammar or even translations.
Ciao,
--
FA
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)
30 Jan
30 Jan
4:15 p.m.
On Jan 28, 2013, at 18:57 05, Fons Adriaensen wrote:
Having been there just a few
hours ago, to me its seems that trying to program for ALSA using
the available (doxygen) documentation is like trying to learn a
new natural language from a dictionary for that language only -
without any grammar or even translations.
I have found that reverse-engineering the sources for the various tools (aplay(1) and
friends) is usually the best way to figure out how to get things done, although there are
sometimes desperate cases where examining the source for alsa-lib itself may be necessary.
Neither fast nor fun, but it does get the job done.
Cheers!
|-------------------------------------------------------------------------|
| Frederick F. Gleason, Jr. | Chief Developer |
| | Paravel Systems |
|-------------------------------------------------------------------------|
| To invent, you need a good imagination and a pile of junk. |
| -- Thomas Edison |
|-------------------------------------------------------------------------|
29 Jan
29 Jan
9:39 a.m.
New subject: Alsa: poll mixer events, always returns true in subsequent calls
Muffinman wrote:
I'm trying to poll mixer events in Alsa using C.
I've used the following
functions within an infinite while loop:
...
snd_hctl_poll_descriptors(hctl, poll_fds, 1);
You are supposed to call snd_hctl_poll_descriptors_count() to get the
number of descriptors.
if (poll_fds[0].revents & POLLIN)
You are supposed to call snd_hctl_poll_descriptors_revents() to get the
events from the descriptors.
While I can get the first mixer event fine, in all
subsequent rounds,
both snd_hctl_wait and poll always return immediately.
You should call snd_hctl_handle_events() to read all the events.
However, calling snd_hctl_handle_events here never
returns
and I can't quite figure out why.
See amixer/amixer.c in the alsa-utils package for an example.
"amixer events" is undocumented for some reason; but does it work?
Regards,
Clemens
4123
days inactive
4125
days old
linux-audio-dev@lists.linuxaudio.org
3 comments
4 participants
participants (4)
-
Clemens Ladisch -
Fons Adriaensen -
Fred Gleason -
Muffinman