[alsa-devel] "Resource temporarily unavailable" while reading although poll returns POLLIN event
dev.c0debabe at gmail.com
Mon Apr 26 10:19:36 CEST 2010
Raymond Yau wrote:
> Are you sure that you really need pulseaudio since your request latency is
> quite low ?
You mean the small period_size of 160 frames or rather the buffer size
In fact at 8kHz sampling rate a period_size of 160 equals a full 20ms of
duration of one frame: 1000ms / 8000Hz = 0.125ms = 125 us
160 frames * 125us = 20000us = 20ms
This is by far more than a large period size holds at a higher sampling
rate (e.g. 44.1 kHz).
To the question whether pulseaudio is needed:
On the embedded target PA will not be used, but since development takes
place on a PC, I need a soundcard that supports the mentioned audio
And at the moment this is pulseaudio which is the reason why I really
need it for application development.
However, we should try to not drift away from the actual problem which
is that *poll() returns an event even if far less than avail_min frames
> You have to ask PA developer whether PA support such low latecny ?
> PA (tsched=0 ) configure your sound card 1792 frames per period but your
> application request for 160 frames per period
> You will need the PA expert to answer how PA server capture 1792 frames from
> sound card and send it to your application
> : module-alsa-source.c: Using 2 fragments of size 7168 bytes, buffer
> time is 81.27ms
> D: alsa-util.c: Its setup is:
> D: alsa-util.c: stream : CAPTURE
> D: alsa-util.c: access : MMAP_INTERLEAVED
> D: alsa-util.c: format : S16_LE
> D: alsa-util.c: subformat : STD
> D: alsa-util.c: channels : 2
> D: alsa-util.c: rate : 44100
> D: alsa-util.c: exact rate : 44100 (44100/1)
> D: alsa-util.c: msbits : 16
> D: alsa-util.c: buffer_size : 3584
> D: alsa-util.c: period_size : 1792
> D: alsa-util.c: period_time : 40634
> D: alsa-util.c: tstamp_mode : ENABLE
> D: alsa-util.c: period_step : 1
> D: alsa-util.c: avail_min : 1792
> D: alsa-util.c: period_event : 0
> D: alsa-util.c: start_threshold : -1
> D: alsa-util.c: stop_threshold : 8070450532247928832
> D: alsa-util.c: silence_threshold: 0
> D: alsa-util.c: silence_size : 0
> D: alsa-util.c: boundary : 8070450532247928832
This is how pulseaudio works *internally*.
Hence it opens my hardware sound card "hw" with the above format.
If sound it recorded/played back at a different sampling rate, PA
If you play a prerecorded audio file that has been recorded at a
different sampling rate, you can see that behavior.
What happens is:
[sound application (e.g.. aplay)] ---(audio format of sound file)---> [
PA plugin] --> [PA daemon] ---(audio format of PA)--> [soundcard]
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