[linux-audio-dev] surround sound project. looking for suggestions

Hi, I am working on a surround sound project. When finished this code will update a virtual acoustic environment based on a persons head motion. I am hoping for some hints on solving a problem I have. Note! My background is in signal processing, not software/hardware interfacing. So I am still clueless on the process of moving data between user memory and the sound card. Current development is done using ALSA. My problem: The current code can process the audio far faster then the sound card can except/output it. Therefore, to reduce the latency between head motion and changes in the sound output, I will need to keep the amount of data in the output buffer to a minimum. For the sake of discussion say about a 1024 frames (the exact amount is flexible) Currently I try to control the flow by pausing the output loop. My problem is that I keep getting buffer underruns, even when I am writing another 1024 frames of data to the sound card before 1024 frames have had time to play (which does not make any sense to me). What I want to do is poll the data buffer so that I can determine the amount of data remaining in the buffer. So far I have only been able to determine (by polling) that the buffer is willing to accept new data. So my question. Does anyone have a idea on how I can determine the percentage of fill in the output buffer? I am also open to any ideas on keeping the amount of data queued for output to a minimum, in a controlled fashion. Thank You Dennis Thompson ******************************************************************* Center for Image Processing and Integrated Computing (CIPIC) Interface Laboratory University of California, Davis CA 95616 Phone : (530) 754-9861 Fax : (530) 752-8894 e-mail : mailto:dmthompson@ucdavis.edu URL : http://interface.cipic.ucdavis.edu/ *******************************************************************