linuxaudio.org

On Thu, Jan 20, 2011 at 7:40 PM, Louis Gorenfeld

 wrote:

quoted text
> Hey, I've been having a lot of trouble with ALSA and processing input

> in a full duplex loop, and I was wondering if anyone here had any

> insight.  I'm using the ALSA poll file descriptor method with the mmap

> routines.  Typically, my processing loop is blowing past the poll

> statement with input requests (POLLIN), causing the CPU usage to go

> off the charts as it's basically looping as fast as it can go.

>

> Now, I'm handling the inputs in a way that might not be correct.

> Often, ALSA is saying that the available frames is 1.5 times my buffer

> size (e.g., I set a 64 sample buffer and ALSA offers me 96 samples).

> I only get (begin/commit) input when the buffer size matches or

> exceeds the buffer length I send out to the card (the set buffer

> size), and if it exceeds that, I only pick up (commit) one buffer's

> length of frames.  Is this wrong?  If there is more input waiting,

> does ALSA immediately go and POLLIN again, or should I expect it to

> not bug me again until I've processed a POLLOUT event (the in and out

> are linked)?  I'm not really sure how to handle this..

the in & out are not linked in any way as far as ALSA is concerned

(even though they may be at the h/w level).
a 64 sample buffer (not period) is very, very small. you need very

tight code and a well configured machine to operate like this. what

period size and/or number of periods are you attempting to use?

_______________________________________________

Linux-audio-dev mailing list

Linux-audio-dev@lists.linuxaudio.org

http://lists.linuxaudio.org/listinfo/linux-audio-dev