This is a followup to my earlier question about dmix not being able to mix small files. I investigated it more and here is what I found.
Again background info. I have a 64KB as kernel buffer and a 64KB circular buffer for my device. In a poll thread I copy the data obtained from ALSA lib from the kernel buffer to my device circular buffer by keeping track of appl_ptr and hw_ptr(dmix only). Everything was working fine except when I was trying to mix files smaller than 64KB(my buffer size), the small file was not getting mixed through the dmix plugin. Anything over 64KB was getting mixed just fine. So I set about reducing my period size from 32KB to 4KB while maintaining my buffer size at 64KB.
When I tried to do this my hw_ptr never gets incremented from 0. Hence my driver is stuck in a loop waiting for bytes to copy. This is only observed when I am using dmix plugin and NOT when using hw or plughw. When my period size is half the size of my buffer everything works fine with dmix (I verified this by reducing my buffer size to 8KB and making my period size 4KB. hw_ptr gets incremented then but I get buffer problems). It seems like dmix is forcing me to keep my period size half the size of my buffer. hw and plughw devices do not seem to do that.
Is this a limitation of dmix. Could anyone comment on the dmix limitation that I am experiencing.
Thanks a lot of all your help.
Prabhu.