bfp_adj.asm

基于ADSP-219x系列的时间抽取基2FFT代码

/******************************************************************************
        Calling Parameters
                Radix-2 DIT FFT stage results in inplacereal and inplaceimag
NOTE: this code assumes inplaceimag immediately follows inplacereal in memory!

        Return Parameters
                inplacereal and inplaceimag adjusted for bit growth

        Altered Registers
                I0,I1,AX0,AY0,AR,MX0,MY0,MR,CNTR

        Altered Memory
                inplacereal, inplaceimag, blk_exponent

*******************************************************************************/
#define      Ntimes2              255  /*N*2-1*/
#define      N_div_2              64
.EXTERN      inplacereal;
.EXTERN      blk_exponent;  
.GLOBAL      bfp_adj;

/* program memory code */
.section/pm program;                
bfp_adj:    AX0=0;
		    DM(blk_exponent)=AX0;
			AX0=CNTR;
            AY0=N_div_2;
            AR=AX0-AY0;
            IF EQ RTS;                           //If last stage, return
            AY0=-2;
            AX0=SB;
            AR=AX0-AY0;                          //Check for SB=-2
            IF EQ RTS;                           //IF SB=-2, no bit growth, return
            I0=inplacereal;                      //I0=read pointer
            I1=inplacereal;                      //I1=write pointer
            AY0=-1;
            MY0=0x4000;                          //Set MY0 to shift 1 bit right
            AR=AX0-AY0,MX0=DM(I0,M1);            //Check if SB=-1; Get first sample
            IF EQ JUMP strt_shift;               //If SB=-1, shift block data 1 bit
            AY0=-2; 	                         //Set AY0 for block exponent update
            MY0=0x2000;                          //Set MY0 to shift 2 bits right
strt_shift: CNTR=Ntimes2;                        //initialize loop counter
            DO shift_loop UNTIL CE;              //Shift block of data
              MR=MX0*MY0(RND),MX0=DM(I0,M1);     //MR=shifted data,MX0=next value
   shift_loop:DM(I1,M1)=MR1; 
			  MR=MX0*MY0(RND);       //Shift last data word
            AY0=DM(blk_exponent);                //Update block exponent and
            DM(I1,M1)=MR1,AR=AY0-AX0;            //store last shifted sample
            DM(blk_exponent)=AR;		
            rts;