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FFTR2B.ASM
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Assembly Source File
|
1990-01-17
|
4KB
|
117 lines
;
; This program originally available on the Motorola DSP bulletin board.
; It is provided under a DISCLAMER OF WARRANTY available from
; Motorola DSP Operation, 6501 Wm. Cannon Drive W., Austin, Tx., 78735.
;
; Radix 2, In-Place, Decimation-In-Time FFT (faster than fftr2a.asm)
;
; Last Update 02 Oct 86 Version 1.1
;
fftr2b macro points,data,coef
fftr2b ident 1,1
;
; Radix 2 Decimation in Time In-Place Fast Fourier Transform Routine
;
; Complex input and output data
; Real data in X memory
; Imaginary data in Y memory
; Normally ordered input data
; Bit reversed output data
; Coefficient lookup table
; -Cosine values in X memory
; -Sine values in Y memory
;
; Macro Call - fftr2b points,data,coef
;
; points number of points (4-32768, power of 2)
; data start of data buffer
; coef start of sine/cosine table
;
; Alters Data ALU Registers
; x1 x0 y1 y0
; a2 a1 a0 a
; b2 b1 b0 b
;
; Alters Address Registers
; r0 n0 m0
; r1 n1 m1
; n2
;
; r4 n4 m4
; r5 n5 m5
; r6 n6 m6
;
; Alters Program Control Registers
; pc sr
;
; Uses 6 locations on System Stack
;
; Latest Revision - September 30, 1986
;
move #points/2,n0 ;initialize butterflies per group
move #1,n2 ;initialize groups per pass
move #points/4,n6 ;initialize coefficient offset
move #-1,m0 ;initialize address modifiers
move m0,m1 ;for linear addressing
move m0,m4
move m0,m5
move #0,m6 ;initialize coefficient address modifier
;for reverse carry (bit reversed) addressing
;
; Do all FFT passes but last pass
;
do #@cvi(@log(points)/@log(2)-0.5),_end_pass
move #data,r0 ;initialize A input pointer
move r0,r4 ;initialize A output pointer
lua (r0)+n0,r1 ;initialize B input pointer
move #coef,r6 ;initialize C input pointer
lua (r1)-,r5 ;initialize B output pointer
move n0,n1 ;initialize pointer offsets
move n0,n4
move n0,n5
do n2,_end_grp
move x:(r1),x1 y:(r6),y0 ;lookup -sine value
move x:(r5),a y:(r0),b
move x:(r6)+n6,x0 ;lookup -cosine value
do n0,_end_bfy ;Radix 3 DIT butterfly kernel with constant
mac x1,y0,b y:(r1)+,y1 ;twiddle factor
macr -x0,y1,b a,x:(r5)+ y:(r0),a
subl b,a x:(r0),b b,y:(r4)
mac -x1,x0,b x:(r0)+,a a,y:(r5)
macr -y1,y0,b x:(r1),x1
subl b,a b,x:(r4)+ y:(r0),b
_end_bfy
move a,x:(r5)+n5 y:(r1)+n1,y1 ;dummy load of x1 and y1
move x:(r0)+n0,x1 y:(r4)+n4,y1
_end_grp
move n0,b1
lsr b n2,a1 ;divide butterflies per group by two
lsl a b1,n0 ;multiply groups per pass by two
move a1,n2
_end_pass
;
; Do last FFT pass
;
move n1,n0 ;correct pointer offset for last pass
move #data,r0 ;initialize A input pointer
move r0,r4 ;initialize A output pointer
lua (r0)+,r1 ;initialize B input pointer
move #coef,r6 ;initialize C input pointer
lua (r1)-n1,r5 ;initialize B output pointer
move x:(r1),x1 y:(r6),y0
move x:(r5),a y:(r0),b
do n2,_lastpass ;Radix 2 DIT butterfly kernel with one
mac x1,y0,b x:(r6)+n6,x0 y:(r1)+n1,y1 ;butterfly per group
macr -x0,y1,b a,x:(r5)+n5 y:(r0),a
subl b,a x:(r0),b b,y:(r4)
mac -x1,x0,b x:(r0)+n0,a a,y:(r5)
macr -y1,y0,b x:(r1),x1 y:(r6),y0
subl b,a b,x:(r4)+n4 y:(r0),b
_lastpass
move a,x:(r5)+n5
endm