Reply by Torgeir Jakobsen ●March 14, 20022002-03-14
Hi

Have you alligned the the FFT data ( AA[] ) at a 32 word boundary. This is
described in the DSP user's guide. The (log2(nx)+1) least significant bits
of the address has to be zero, nx is the fft size.
Thus, in your case log2(16)+1 = 5, i.e. the fft data has to start at a
address where the 5 least significant bits are 0.
This can be done as follows:

1) Create a section where the data are placed

#pragma DATA_SECTION(AA,".fftdata")
short AA[16];

2) Use this section name in the linker command file together with align(32)
as shown in the example below

MEMORY
{
PAGE 0: SCRATCH: origin=0x0060, length=0x0020 /* Scratch-Pad RAM */
PAGE 0: VECTOR: origin=0x0080, length=0x0078 /* Space for int. vectors */
PAGE 0: PROGRAM: origin=0x00F8, length=0x1C00 /* Space for program code */
PAGE 1: PROGDATA: origin=0x1D00, length=0x2300 /* Space for data */
}

SECTIONS
{
.vectors >VECTOR PAGE 0
.text >PROGRAM PAGE 0
.cinit >PROGRAM PAGE 0
fasttext >PROGRAM PAGE 0
.sintab >PROGDATA PAGE 1
.bss >PROGDATA PAGE 1
.data >PROGDATA PAGE 1
.const >PROGDATA PAGE 1
.stack >PROGDATA PAGE 1
.fftdata: >PROGDATA PAGE 1, align(32)
}

Best regards
Torgeir Jakobsen
Senior Engineer, Technology Department
Aanderaa Instruments AS
e-mail:
web: www.aanderaa.com
phone; +47 55 10 99 00
direct: +47 55 10 99 77
fax: +47 55 10 99 10
----- Original Message -----
From: "ykm67111" <>
To: <>
Sent: Wednesday, March 13, 2002 8:41 AM
Subject: [c54x] About FFT ( using dsplib ) > I am using TI TMSC5402 DSK and dsplib V2.1 now.
> My problem is I can't get the correct FFT values.
> But I can't find what is wrong?
> I test a 16 point float point data.
> Ex:
> float A[16]={0.001,0.002,0.003,0.004,
> 0.005,0.006,0.007,0.008,
> 0.009,0.010,0.011,0.012,
> 0.013,0.014,0.015,0.016};
> short AA[16];
> short NX;
>
> And I follow the next steps to do FFT .
>
> scale=0;
> fltoq15(A,AA,NX);
> cbrev(AA,AA,(ushort)NX/2);
> rfft16(AA,scale);
>
> Can anyone tell me which step I do is wrong??
>
> Thanks!! >
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Reply by ykm67111 ●March 13, 20022002-03-13
I am using TI TMSC5402 DSK and dsplib V2.1 now.
My problem is I can't get the correct FFT values.
But I can't find what is wrong?
I test a 16 point float point data.
Ex:
float A[16]={0.001,0.002,0.003,0.004,
0.005,0.006,0.007,0.008,
0.009,0.010,0.011,0.012,
0.013,0.014,0.015,0.016};
short AA[16];
short NX;

And I follow the next steps to do FFT .

scale=0;
fltoq15(A,AA,NX);
cbrev(AA,AA,(ushort)NX/2);
rfft16(AA,scale);

Can anyone tell me which step I do is wrong??

Thanks!!