RM0020 datasheet(16/69 Pages) STMICROELECTRONICS

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Function API

RM0020

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Algorithm:

Equation 1

for each n from 0 to N-1

Equation 2

where i is the imaginary unit with the property that:

Note: There must be at least 32 bytes of readable memory behind inout_buffer.

Performance: See Section 7 and Table 32.

Example 3. fft_radix4_float

#include "libdsp2.h"

float inout_buffer[2*256];

void main() {

/* bit reverse permutation and calculation of 256-point FFT */

bitrev_table_32bit(16, inout_buffer, seed_radix4_32bit_256);

fft_radix4_float (256, inout_buffer, w_table_radix4_float_256);

}

6.4

N-point radix-4 complex to complex frac16/frac32 in-place

FFT

Function call:

void fft_radix4_frac32(unsigned int N, int *inout_buffer,

int *twiddle_factor_table);

Arguments:



 w



–



i

--------

–

Table 4.

fft_radix4_frac32 arguments

Nin

FFT length, must be even power of two, tested for 64, 256,

1024, 4096

inout_buffer

in/out

pointer to the input/output vector of length 2*N, vector must be

double word aligned

input data alignment:

16-bit fractional input data in range -1 to 1-2^-15 are stored in

second half of inout_buffer in order real, imag, real imag, .....

0, 0, 0, 0, ... x_Re(0) x_Im(0), x_Re(1) x_Im(1), ... x_Re(N-1)

x_Im(N-1),

output data alignment:

32-bit fractional output data in range -1 to 1-2^-31 are stored:

X_Re(0) X_Im(0) X_Re(1) X_Im(1) ... X_Re(N-1) X_Im(N-1)

(Re - real part, Im - imaginary part)

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