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 of 2*period_size?
In fact at 8kHz sampling rate a period_size of 160 equals a full 20ms of sound:
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 format contraints. 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 are available*.
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 converts it. 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]
cheers, stefan