[alsa-devel] how many processed frames? + various thoughts

Hello all, I'm rather new to ALSA development. I would like to build a little loop-player driven by a beat counter and a good mail exchange from linuxaudio.org gave me a smart solution: to count the beat bars into the audio thread. Knowing the sample rate and the processed samples, I'm able to calculate the clock (what do you think about this approach?). And now my question: is there a good function into alsa API which returns the number of processed frames? Or even better, is it possibile to fire a callback after N frames? Thank you in advance (and sorry for my English)!

JJ