On Sat, 20 Dec 2008 19:44:33 +0530 "SUBHRANIL CHOUDHURY" subhra85@gmail.com wrote:

I have some doubts on the ALSA programming, 1)My ALSA driver supports minimum Period Bytes size as 32 bytes, but when i set the period size as 512 bytes it is always setting to 1024 bytes.I am using the function "snd_pcm_hw_params_set_period_size_near()" . What might be wrong here?Is the function what i am using correct?

pcm.h:int snd_pcm_hw_params_set_period_size_near(snd_pcm_t *pcm, snd_pcm_hw_params_t *params, snd_pcm_uframes_t *val, int *dir);

That function gets the number of *frames*, not bytes. If you are setting up a pcm device to play a 1 channel, 16 bits sound, then 512 frames are 1024 bytes long. Note that even if the hardware supports a feature, the driver may not.

2)How the Library functions and the Driver functions interact, what is the interface between the library functions and driver functions?Is there any document which explains this. I got a document which explains how to write ALSA driver.But it does not mention the interface with the library.

You shouldn't care on how alsa-lib and alsa-kernel interact, unless you are writing some low-level stuff. In that case, I guess you have to dig into the sources :) If you find good docs on alsa-lib let me know...

3)How Can we achive MIC and LINEIN switching using the mixer?What library function do i need to use to achive this?

You have to use the control interface. Each card is different, but naming conventions usually make easy to locate the right switch. For example:

$ amixer contents [...] numid=146,iface=CARD,name='Digital mode Switch' ; type=ENUMERATED,access=rw------,values=1,items=3 ; Item #0 'S/PDIF Coaxial' ; Item #1 'S/PDIF Optical' ; Item #2 'ADAT Optical' : values=0 numid=149,iface=CARD,name='Phantom power Switch' ; type=BOOLEAN,access=rw------,values=1 : values=off [...]

4)If i want to get the Timestamp for each buffer captured, what library function should be used?

5)I am trying to capture and play the same audio (ALSA duplex). When i capture and store it in a file and play from the file i am able to hear the sound properly. If i capture in a buffer and play the same buffer directly it says Broken PIPE ERROR in the playout. I tried the capture and playout in two different threads, i am able to hear the sound and i am not getting any Broken PIPE error. But along with the audio i am hearing some noise. Do we need to use some kind of synchronisation between the threads for capture and playout?

I can't help here.

-- Giuliano.