Why variables are not stored as zero in stm32cubeid? - c

Question

samples different from 0
I am working with the stm32cubeid platform and the stm32f407ve development board, I am trying to sample a sinusoidal signal that I generate in the same compiler and apply the fast fourier transform functions. When displaying the variables after applying the fft the spaces that They should have a 0 stored, according to the code, negative or positive values close to 0 appear, this does not affect the operation of the code, but I do not understand why this happens.This is all I have written in the generated code generated with the stm32cubeid.
#include "main.h"
#include "arm_math.h"
#include "arm_const_structs.h"
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
/* USER CODE END Includes */
/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */
#define Fs 4096;
/* USER CODE END PTD */
/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
/* USER CODE END PD */
/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */
/* USER CODE END PM */
/* Private variables ---------------------------------------------------------*/
ADC_HandleTypeDef hadc1;
/* USER CODE BEGIN PV */
#define SIGNAL_BUFFER_LENGTH 4096
float signalBuffer[2*SIGNAL_BUFFER_LENGTH];
float fftBuffer[2*SIGNAL_BUFFER_LENGTH];
float magnitudes[SIGNAL_BUFFER_LENGTH];
/* USER CODE END PV */
uint32_t k;
uint32_t cont1,cont2;
uint32_t start;
uint32_t stopi;
uint32_t delta;
float32_t maxValue; /* Max FFT value is stored here */
uint32_t maxIndex;
float frecuencia=10.0;
float32_t Ts;
float tiempo;
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_ADC1_Init(void);
/* USER CODE BEGIN PFP */
/* USER CODE END PFP */
/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
/* USER CODE END 0 */
/**
* #brief The application entry point.
* #retval int
*/
int main(void)
{
/* USER CODE BEGIN 1 */
/* USER CODE END 1 */
/* MCU Configuration--------------------------------------------------------*/
/* Reset of all peripherals, Initializes the Flash interface and the Systick. */
HAL_Init();
/* USER CODE BEGIN Init */
#define ARM_CM_DEMCR (*(uint32_t*)0xE000EDFC)
#define ARM_CM_DWT_CTRL (*(uint32_t*)0xE0001000)
#define ARM_CM_DWT_CYCCNT (*(uint32_t*)0xE0001004)
if(ARM_CM_DWT_CTRL !=0){
ARM_CM_DEMCR |= 1<<24;
ARM_CM_DWT_CYCCNT =0;
ARM_CM_DWT_CTRL |= 1<<0;
}
/* USER CODE END Init */
/* Configure the system clock */
SystemClock_Config();
/* USER CODE BEGIN SysInit */
/* USER CODE END SysInit */
/* Initialize all configured peripherals */
MX_GPIO_Init();
MX_ADC1_Init();
/* USER CODE BEGIN 2 */
Ts=1.0/(float)Fs;
for(k=0;k<2*SIGNAL_BUFFER_LENGTH;k+=2 )
{
signalBuffer[k]=10*(float)sin(2*PI*k/2*Ts*frecuencia);
signalBuffer[k+1]=0;
}
//k++;
start= ARM_CM_DWT_CYCCNT;
arm_cfft_f32(&arm_cfft_sR_f32_len4096,signalBuffer,0,1);
arm_cmplx_mag_f32(signalBuffer,magnitudes,4096);
arm_max_f32(magnitudes, 4096, &maxValue, &maxIndex);
stopi = ARM_CM_DWT_CYCCNT;
delta=stopi-start;
tiempo=delta/8.0E07*1000.0;
/* USER CODE END 2 */
/* Infinite loop */
/* USER CODE BEGIN WHILE */
while (1)
{
/* USER CODE END WHILE */
/* USER CODE BEGIN 3 */
}
/* USER CODE END 3 */
}