Polled audio playback

Hi guys!
Anybody konows how to play sound samples with polling? I mean there is
my callback routine and I want it to be called each time sound buffer is
played it’s half. Just like standart playback scheme: when we plays
first half we fill up second and vice versa. Don’t blame me , I just a
newbie :)–
With best regards Razor.X.Jackie
"The choise is yours… walk now and live or stay and die"