* initialization
n equ 20
start equ $40
wddr equ $0
cddr equ $0
input equ $ffe0
output equ $ffe1
;
org p:start
move #wddr,

r0

;r0 ¬ samples
move #cddr,

r4

;r1 ¬ coefficients
move #n-1,m0 ;set modulo arithmetic
move m0,m4 ;for the 2 circular buffers
;
opt cc
; filter loop :8+(n-1) cycles

movep y:input,x: (

r0

) ;input sample in memory
clr a x:(

r0

)+,x0 y: (

r4

)+,y0
rep #n-1
mac x0,y0,a x:(

r0

)+,x0 y:(

r4

)+,y0
macr x0,x0,a (

r0

)-

movep a,y:output ;output filtered sample

fftr2a macro points,data,coef
fftr2a: ident 1,1

move #points/2,n0 ;initialize butterflies per group
move #1,n2 ;initialize groups per pass
move #points/4,n6 ;initialize C pointer offset
move #-1,m0 ;initialize A and B address modifiers
move m0,m1 ;for linear addressing
move m0,m4
move m0,m5
move #0,m6 ;initialize C address modifier for
;reverse carry (bit-reversed) addressing

do #@cvi (@log(points)/@log(2)+0.5),_end_pass
move #data,

r0

;initialize A input pointer
move

r0

,

r4

;initialize A output pointer

_end_bfy
move a,x:(

r5

)+n5 y:(

r1

)+n1,y1

end_cell
rnd a
movep #0,x:$fffe
dc @sin(@cvf(count)*freq)
move #twiddle,

r2

MOVE L:<$1,A
SUB X,A L:<$3,B

bad_label
good_label: