; Example 3 - 41. Complex DIT Radix-4 FFT ASM Listing for the TMS320C3x DSP
*
.GLOBAL FFT ; ENTRY POINT FOR EXECUTION
.GLOBAL N ; FFT SIZE
.GLOBAL M ; LOG4(N)
.GLOBAL SINE ; ADDRESS OF SINE TABLE
*
INP .USECT "IN",1024 ; MEMORY WITH INPUT DATA
*
.TEXT
*
8 INITIALIZE
*
.WORD FFT ; STARTING LOCATION OF THE PROGRAM
*
.SPACE 100 ; RESERVE 100 WORDS FOR VECTORS, ETC.
*
TEMP .WORD $+2
STORE .WORD FFTSIZ ; BEGINNING OF TEMP STORAGE AREA
.WORD N
.WORD M
.WORD SIZE
.WORD INP
*
.BSS FFTSIZE,1 ; FFT SIZE
.BSS LOGFFT,1 ; LOG4(FFTSIZE)
.BSS SINTAB,1 ; SINE/COSINE TABLE BASE
.BSS INPUT,1 ; AREA WITH INPUT DATA TO PROCESS
.BSS STAGE,1 ; FFT STAGE #
.BSS RPTCNT,1 ; REPEAT COUNTER
.BSS IEINDX,1 ; IE INDEX FOR SINE/COSINE
.BSS LPCNT,1 ; SECOND-LOOP COUNT
.BSS JT,1 ;JT COUNTER IN PROGRAM, P. 117
.BSS IA1,1 ; IA1 INDEX IN PROGRAM, P. 117
*
FFT:
*
LDP TEMP ; INITIALIZE DATA LOCATIONS
LDI @TEMP,AR0 ;COMMAND TO LOAD DATA PAGE POINTER
LDI @STORE,AR1
LDI *AR0++,R0 ; XFER DATA FROM ONE MEMORY TO THE
* ; OTHER
STU R0,*AR1++
LDI *AR0++,R0
STI R0,*AR1==
LDI *AR0++,R0
STI R0,*AR1++
LDI *AR0,R0
STI R0,8AR1
*
LDP FFTSIZ ; COMMAND TO LOAD DATA PAGE POINTER
LDI @FFTSIZ.R0
LDI @FFTSIZ,IR0
LDI @FFTSIZ,IR1
LDI 0,AR7
STI AR7,@STAGE ; @STAGE HOLDS THE CURRENT STAGE
* ; MEMBER
LSH 1,IR0 ; IR0=2*N1 (BECAUSE OF REAL/IMAG)
LSH -2,IR1 ; IR1=N/4, POINTER FOR SIN/COS TABLE
LDI 1,AR7
STI AR7,@RPTCNT ; INITIALIZE REPEAT COUNTER OF FIRST
* ; LOOP
LSH -2,R0
STI AR7,@IEINDX ; INITIALIZE TE INDEX
ADDI 2,R0
STI R0,@JT ; JT=R0/2+2
SUBI 2,R0
LSH 1,R0 ; R0=N2
*
* OUTER LOOP
LOOP:
LDI @INPUT,AR0 ; AR0 POINTS TO X(I)
ADD R0,AR0,AR1 ; AR1 POINTS TO X(I1)
ADDI R0,AR1,AR2 ; AR2 POINTS TO X(I2)
ADDI R0,AR2,AR3 ; AR3 POINTS TO X(I3)
LDI @RPTCNT,RC
SUI 1,RC ; RC SHOULD BE ONE LESS THAN DESIRED #
*
* FIST LOOP
*
RPTB BLK1
ADDF *+AR0,*+AR2,R1 ; R1=Y(I)+Y(I2)
ADDF *+AR3,*+AR1,R3 ; R3=Y(I1)+Y(I3)
ADDF R3,R1,R6 ; R6=R1+R3
SUBF *+AR3,*+AR0,R4 ; R4=Y(I)-Y(I2)
STF R6,*+AR0 ; Y(I)=R1+R3
SUBF R3,R1 ; R1=R1-R3
LDF *AR2,R5 ; R5=X(I2)
|| LDF *+AR1,R7 ; R7=Y(I1)
ADDF *AR3,*AR1,R3 ; R3=X(1)+X(I3)
ADDF R5,*AR0,R1 ; R1=X(I)+X(I2)
|| STF R1,*+AR1 ; Y(I1)=R1-R3
ADDF R3,R1,R6 ; R6=R1+43
SUBF R5,*AR0,R2 ; R2=X(I)-X(I2)
|| STF R6,*AR0++(IR0) ; X(I)=R1+R3
SUBF R3,R1 ; R1=R1-R3
SUBF *AR3,*AR1,R6 ;R6=X(I1)-X(I3)
SUBF R7,*+AR3,R3 ; -R3=Y(I1)-Y(I3) !!!
|| STF R1,*AR1++(IR0) ; X(I1)=R1-R3
SUBF R6,R4,R5 ; R5=R4-R6
ADDF R6,R4 ; R4=R4+R6
STF R5,*+AR2 ;Y(I2)=R4-R6
|| STF R4,*+AR3 ; Y(I3)=R4+R6
SUBF R3,R2,R5 ; R5=R2-R3 !!!
ADDF R3,R2 ; R2=R2+R3 !!!
BLK1 STF R5,*AR2++(IR0) ; X(I2)=R2-R3 !!!
|| STF R2.*AR3++(IR0) ; X(I3)=R2+R3 !!!
*
* IF THIS IS THE LAST STAGE, YOU ARE DONE
*
LDI @STAGE,AR7
ADDI 1,AR7
CMPI @LOGFFT,AR7
BZD END
STI AR7,@STAGE ; CURRENT FFT STAGE
*
* MAIN INNER LOOP
*
LDI 1,AR7
STI AR7,@IA1 ; INIT IA1 INDEX
LDI 2,AR7
STI AR7,@LPCNT ; INIT LOOP COUNTER FOR INNER LOOP
INLOP:
LDI 2,AR6 ; INCREMENT INNER LOOP COUNTER
ADDI @LPCNT,AR6
LDI @LPCNT,AR0
LDI @IA1,AR7
ADDI @IEINDX,AR7 ; IA1=IA1+IE
ADDI @INPUT,AR0 ; (X(I),Y(I)) POINTER
STI AR7,@IA1
ADDI R0,AR0,AR1 ; (X(I1),Y(I1)) POWER
STI AR6,@LPCNT
ADDI R0,AR1,AR2 ; (X(I2),Y(I2)) POINTER
ADDI R0,AR2,AR3 ; (X(I3),Y(I3)) POINTER
LDI @RPTCNT,RC
SUBI 1,RC ; RC SHOULD BE ONE LESS THAN DESIRED #
CMPI @JT,AR6 ; IF LPCNT=JT, GO TO
BZD SPCL ; SPECIAL BUTTERFLY
LDI @IA1,AR7
LDI @IA1,AR4
ADDI @SINTAB,AR4 ; CREATE COSINE INDEX AR4
ADDI AR4,AR7,AR5
SUBI 1,AR5 ; IA2=IA1+IA1-1
ADDI AR7,AR5,AR6
SUBI 1,AR6 ; IA3=IA2+IA1-1
*
* SECOND LOOP
*
RPTB BLK2
ADDF *+AR2,*+AR0,R3 ; R3=Y(I)+Y(I2)
ADDF *+AR3,*+AR1,R5 ; R3=Y(I1)+Y(I3)
ADDF R5,R3,R6 ; R6=R3-R5
SUBF *+AR2,*+AR0,R4 ; R4=Y(I)-Y(I2)
SUBF R5,R3 ; R3=R3-R5
ADDF *AR2,*AR0,R1 ; R1=X(I)+X(I2)
ADDF *AR3,*AR1,R5 ; R5=X(II)+X(I3)
MPYF R3,*+AR5(IR1),R6 ; R6=R3+C02
|| STF R6,*+AR0 ; Y(I)=R3+R5
ADDF R5,R1,R7 ; R7=R1+R5
SUBF *AR2,*AR0,R2 ; R2=X(I)-X(I2)
SUBF R5,R1 ; R1=R1-R5
MPYF R1,AR5,R7 ; R7=R1*SI2
|| STF R7,*AR0++(IR0) ; X(I)=R1+R5
SUBF R7,R6 ; R6=R3*C02-R1*SI2
SUBF *AR3,*AR5(IR1),R7 ; R5=Y(I1)-Y(I3)
MPYF R1,*+AR5(IR1),R7 ; R7=R1*C02
|| STF R6,*+AR1 ; Y(I1)=R3*C02-R1*SI2
MPYF R3,*AR5,R6 ; R6=R3*SI2
ADDF R7,R6 ; R6=R1*C02+R3*sI2
ADDF R5,R2,R1 ; R1=R2+R5
SUBF R5,R2 ; R5=X(I1)-X(I3)
SUBF R5,R4,R3 ; R3=R4-4T
ADDF R5,R4 ; R4=R4+R5
MPYF R3,*+AR4(IR1),R6 ; R6=R3*C01
|| STF R6,*AR1++(IR0) ; X(I1)=R1*C02+R3*SI2
MPYF R1,*+AR4,R7 ; R7=R1*SI1
SUBF R7,R6 ; R6=R3*C01+R1*SI1
MPYF R1,*AR4++(IR1),R6 ; R6=R1*C01
|| STF R6,*+AR2 ; Y(I2)=R3*C01-R1*SI1
MPYF R3,*AR4,R7 ; R7=R3*SI1
ADDF R7,R6 ; R6=R1*C01+R3*SI1
MPYF R4,*+AR6(IR1),R6 ; R6=R4*C03
|| STF R5,*AR2++(IR0) ; X(I2)=R1*C01+R3*SI1
MPYF R2,*AR6,R7 ; R7=R2*SI3
SUBF R7,R6 ; R6=R4*C03-R2*SI3
MPYF R2,*+AR6(IR1),R6 ; R6=R2*C03
|| STF R6,*+AR3 ; Y(I3)=R4*C03-R2*SI3
MPYF R4,*AR6,R7 ; R7=R4*SI3
ADDF R7,R6 ; R6=R2*C03+R4*SI3
BLK2 STF R6,*AR3**(IR0) ; X(I3)=R2*C03+R4*SI3
*
CMPI @LPCNT,R0
BP INLOP ;LOOP BACK TO THE INNER LOOP
BR CONT
*
* SPECIAL BUTTERFLY FOR W=J
*
SPCL LDI IR1,AR4
LSH -1,AR4 ;POINT TO SIN(45)
ADDI @SINTAB,AR4 ;CREATE COSINE INDEX AR4=CO21
*
RPTB BLK3
ADDF *AR2,*AR0,R1 ;R1=X(I)+X(I2)
SUBF *AR2,*AR0,R2 ;R2=X(I)-X(I2)
ADDF *+AR2,*+AR0,R3 ;R3=Y(I)+Y(I2)
SUBF *+AR2,*+AR0,R4 ;R3=Y(I)-Y(I2)
ADDF *AR3,*AR1,R5 ;R5=X(I1)+X(I3)
SUBF R1,R5,R6 ;R6=R5-R1
ADDF R5,R1 ;R1=R1+R5
ADDF *+AR3,*+AR1,R5 ;R5=Y(I1)-Y(I3)
SUBF R5,R3,R7 ;R7=R3-R5
ADDF R5,R3 ;R3=R3+R5
STF R3,*+AR0 ;Y(I)=R3+R5
|| STF R1,*AR0++(IR0) ;X(I)=R1+R5
SUBF *AR3,*AR1,R1 ;R1=X(I1)-X(I3)
SUBF *+AR3,*+AR1,R3 ;R3=Y(I1)-Y(I3)
STF R6,*+AR1 ;Y(I1)=R5-R1
|| STF R7,*AR1++(IR0) ;X(I1)=R3-R5
ADDF R3,R2,R5 ;R5=R2+R3
SUBF R2,R3,R2 ;R2=-R2+R3
SUBF R1,R4,R3 ;R3=R4-R1
ADDF R1,R4 ;R4=R4+R1
SUBF R5,R3,R1 ;R1=R3-R5
MPYF *AR4,R1 ;R1=R1*C021
|| STF R1,*+AR2 ;Y(I2)=(R3-R5)*C021
SUBF R4,R2,R1 ;R1=R2-R4
MPYF *AR4,R1 ;R1=R1*C021
|| STF R3,*AR2++(IR0) ;X(I2)=(R3+R5)*C021
ADDF R4,R2 ;R2=R2+R4
MPYF *AR4,R2 ;R2=R2*C021
BLK3 STF R1,*+AR3 ;Y(I3)=-(R4-R2)*C021
|| STF R2,*AR3++(IR0) ;X(I3)=(R4+R2)*C021
*
*
CMPI @LPCNT,R0
BPD INLOP ;LOOP BACK TO THE INNER LOOP
*
CONT LDI @RPTCNT,AR7
LDI @IEINDX,AR6
LSH 2,AR7 ;INCREMENT REPEAT COUNTER FOR NEXT
* ;TIME
STI AR7,@RPTCNT
LSH 2,AR6 ;IE=4*IE
STI AR6,@IEINDX
LDI R0,IR0 ;N1=N2
LSH -3,R0
ADDI 2,R0
STI R0,@JT ;JT=N2/2+2
SUBI 2,R0
LSH 1,R0 ;N2=N2/4
BR LOOP ;NEXT FFT STAGE
*
* STORE RESULT OUT USING BIT-REVERSED ADDREDDING
*
END: LDI @FFTSIZ,RC ;RC=N
SUBI 1,RC ;RC SHOULD BE ONE LESS THAN DESIRED
LDI @FFTSIZ,IR0 ;IR0=SIZE OF FFT=N
LDI 2,IR1
LDI @INPUT,AR0
LDP STORE
LDI @STORE,AR1
*
RPTB BITRV
LDF *+AR0(1),R0
|| LDF *AR0++(IR0)B,R1
BITRV STF R0,*+AR1(1)
|| STF R1,*AR1++(IR1)
*
SELF BR SELF ;BRANCH TO ITSELF AT THE END
.END
