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Hi all, A new group for Hungarian DSP users: Subscribe: Owner: Web: http://lista.prim.hu Usful informations: There is an fft program example in the book "ADSP-218x DSP Istruction Set Reference" on the page 3-14. It is Radix-2 Decimation-In-Time fft. I found some errors in it, missing instuctions, worng register and fractional mode using, srcambling errors etc... I'm trying to fix it, but I can't understand, how the block exponent scaling works. The code is below. The rows which i don't understand are questionmaked in the comment. The MAC is used for shifting a word one or two bit right. But in real, it shifts the words by two or four bits right. What is the reason for it? Why is 1 or 2 bit is written in the comments, and why shifts the MAC 2 or 4 bits right? If somebody need the full code, plz wirte me! (not fully corrected yet!) Thanks and regards Sandor .GLOBAL bfp_adj; bfp_adj: AY0 = DM(_stage_cnt); // check for last stage AR = AY0 -1; IF EQ RTS; // if last, rts AY0 = -2; AX0 = SB; AR = AX0 - AY0; // check for sb=-2 IF EQ RTS; // if sb=-2, no bit growth, rts I0 = inplacereal; // read ptr I1 = inplacereal; // write ptr AY0 = -1; MY0 = 0X4000; // set my0 to shift 1 bit right ???? AR = AX0 - AY0 , MX0 = DM(I0,M1); //check if sb=-1 IF EQ JUMP strt_shift; //get 1st sample AY0 = -2; // set ay0 for block exponent update MY0 = 0X2000; // set my0 to shift 2 bits right ???? strt_shift: ax1 = DM(_Ntimes2_1); // Ntimes2 - 1 CNTR = ax1; DO shift_loop UNTIL CE; MR = MX0 * MY0(RND), MX0 = DM(I0,M1);//mr=shifted data,mx0=next value shift_loop: DM(I1,M1) = MR1; //shifted data MR = MX0 * MY0(RND); //shift last data word AX0 = DM(blk_exponent); //update block exponent DM(I1,M1) = MR1, AR = AX0 - AY0; //and store last shifted sample DM(blk_exponent) = AR; RTS; |
fft & new dsp group
Started by ●January 13, 2004
