UM0585

Complex 16-bit radix-4 FFT

Doc ID 14988 Rev 2

11/25

3.2.2

cr4_fft_256_stm32

function

Table 6 describes the cr4_fft_256_stm32 function.

3.2.3

cr4_fft_1024_stm32

function

Table 7 describes the cr4_fft_1024_stm32 function.

Example

#define N 64 /*Number of points*/

uint32_t x[N],y[N]; /* input and output arrays */

uint16_t real[N], imag[N]; /* real and imaginary arrays */

/* Fill the input array */

for(i=0; i<N; i++)

x[i] = (((uint16_t)(real[i])) | ((uint32_t)(imag[i]<<16)));

cr4_fft_64_stm32(y, x, N); /*computes the FFT of the x[N] samples*/

3.3

FFT performance improvement

The FFT coefficients table is stored in the Flash memory since it is declared as code in the

assembly file. The performance of the FFT function can be improved by placing the FFT

coefficients in RAM. This is done as described below:

Table 6.

cr4_fft_256_stm32

function

Function name

cr4_fft_256_stm32

Prototype

void cr4_fft_256_stm32(void *pssOUT, void *pssIN,

uint16_t Nbin);

Behavior description

complex 16-bit, 256-point radix-4 FFT

Input parameter

– pssOUT: pointer to the output array data

– pssIN: pointer to the input array data

– Nbin: the number of points, must be 256.

Output parameter

None

Return parameter

None

Table 7.

cr4_fft_1024_stm32

function

Function name

cr4_fft_1024_stm32

Prototype

void cr4_fft_1024_stm32(void *pssOUT, void *pssIN,

uint16_t Nbin);

Behavior description

complex 16-bit, 1024-point radix-4 FFT

Input parameter

– pssOUT: pointer to the output array data

– pssIN: pointer to the input array data

– Nbin: the number of points, must be 1024.

Output parameter

None

Return parameter

None