RM0020 datasheet(19/69 Pages) STMICROELECTRONICS

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RM0020

Function API

19/69

void main() {

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

bitrev_table_32bit(16, inout_buffer, seed_radix2_32bit_256);

fft_quad_float(256, inout_buffer, w_table_radix2_float_256);

}

6.6

N-point quad radix-2 complex to complex frac16/frac32 in-

place FFT

Function call:

void fft_quad_frac32(unsigned int N, int *inout_buffer,

int *twiddle_factor_table);

Arguments:

Description:

Computes the N-point quad radix-2 complex to complex frac16/frac32 in-place fast

Fourier transform (FFT). Input bit reversed 16-bit fractional data are stored in second

half of inout_buffer, output 32-bit fractional data are written over the input data into

inout_buffer. There is used radix-2 algorithm in which two stages are calculated in

one loop (quad butterfly).

The output scaling is configurable by constant definition in the function source file:

.set

SCALING

#/* 0 - off, 1 - on */

Table 6.

fft_quad_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)

twiddle_factor_table in

pointer to the vector of twiddle factors of length N, vector must

be double word aligned

memory layout:

w_Re(0) w_Im(0) w_Re(1) w_Im(1) ... w_Re(N/2-1) w_Im(N/2-

Use predefined w_table_radix2_frac32_N arrays.

The w_table_radix2_frac32_N is computed according to this

formula:

for k = 0, 1, ... N/2-1

w_Re k

 iw_Im k





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