Producing tone with Audio Codec on NIOS II?

Hey everyone,

I'm just learning how to use the Audio CODEC on NIOS II with the DE2 board. I wrote the following assembly code to generate a square wave and use it to produce an output tone:

.equ ADDR_AUDIODACFIFO, 0x10003040


.global main
main:
movia r2, ADDR_AUDIODACFIFO


#Set up the square wave's positive pulse
preloop1:
movi r3, 10000
movi r4, 22


#Send 22 outputs to the FIFO
loop1:
stwio r3, 8(r2)
stwio r3, 12(r2)
subi r4, r4, 1
beq r4, r0, preloop2
br loop1


#Set up the square wave's negative pulse
preloop2:
movi r3, -10000
movi r4, 22


#Send 22 outputs to the FIFO
loop2:
stwio r3, 8(r2)
stwio r3, 12(r2)
subi r4, r4, 1
beq r4, r0, preloop1
br loop2

It doesn't seem to be working - nothing is being written to the audio codec's FIFOs. Does anyone know what I need to do to produce a tone? Thanks.