Audio IP Core: how to reproduce a sound

Hi,

I'm trying to develop a program with Altera DE2 and Audio IP Core.

I declared in memory a wave file just as an array of 32-bits elements.

Here it is the code:

alt_up_audio_reset_audio_core();
lw = alt_up_audio_write_left_channel(notify, LEN);
rw = alt_up_audio_write_right_channel(notify, LEN);
printf ("lw: %d rw: %d\n\n", lw, rw);

lw and lr remain stuck to 128,while the array is much longer. it seems the FIFO doesn't empty by itself and the sound is not reproduced. So, how can I make it reproduced?