编写一个STM32通过FFT计算分贝值程序

要编写一个STM32通过FFT计算分贝值的程序，需要进行以下步骤：

1. 创建一个工程，并添加CMSIS库和FFT库。

2. 配置ADC模块，从麦克风或音频输入获取数据，并使用DMA传输到内存中。

3. 配置FFT模块，将ADC采集的数据进行FFT变换。

4. 计算FFT的模值，并将其转换为分贝值。

下面是一个简单的示例代码，可以作为参考：

#include "arm_math.h"
#include "stm32f4xx.h"

#define FFT_SIZE 1024
#define SAMPLE_RATE 44100

static uint16_t adc_buffer[FFT_SIZE];
static float32_t fft_buffer[FFT_SIZE];

void ADC_Configuration(void)
{
  ADC_InitTypeDef ADC_InitStructure;
  DMA_InitTypeDef DMA_InitStructure;
  
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA2, ENABLE);
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1, ENABLE);
  
  DMA_InitStructure.DMA_Channel = DMA_Channel_0;
  DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&ADC1->DR;
  DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t)adc_buffer;
  DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory;
  DMA_InitStructure.DMA_BufferSize = FFT_SIZE;
  DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
  DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
  DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;
  DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;
  DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;
  DMA_InitStructure.DMA_Priority = DMA_Priority_High;
  DMA_InitStructure.DMA_FIFOMode = DMA_FIFOMode_Disable;
  DMA_InitStructure.DMA_FIFOThreshold = DMA_FIFOThreshold_HalfFull;
  DMA_InitStructure.DMA_MemoryBurst = DMA_MemoryBurst_Single;
  DMA_InitStructure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;
  DMA_Init(DMA2_Stream0, &DMA_InitStructure);
  DMA_Cmd(DMA2_Stream0, ENABLE);

  ADC_InitStructure.ADC_Resolution = ADC_Resolution_12b;
  ADC_InitStructure.ADC_ScanConvMode = DISABLE;
  ADC_InitStructure.ADC_ContinuousConvMode = ENABLE;
  ADC_InitStructure.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_None;
  ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;
  ADC_InitStructure.ADC_NbrOfConversion = 1;
  ADC_Init(ADC1, &ADC_InitStructure);

  ADC_RegularChannelConfig(ADC1, ADC_Channel_0, 1, ADC_SampleTime_3Cycles);
  ADC_DMARequestAfterLastTransferCmd(ADC1, ENABLE);
  ADC_DMACmd(ADC1, ENABLE);

  ADC_Cmd(ADC1, ENABLE);
}

void FFT_Configuration(void)
{
  arm_cfft_radix4_instance_f32 fft_inst;
  arm_cfft_radix4_init_f32(&fft_inst, FFT_SIZE, 0, 1);
  
  while (1) {
    if (DMA_GetFlagStatus(DMA2_Stream0, DMA_FLAG_TCIF0)) {
      DMA_ClearFlag(DMA2_Stream0, DMA_FLAG_TCIF0);
      arm_q15_to_float(adc_buffer, fft_buffer, FFT_SIZE);
      arm_cfft_radix4_f32(&fft_inst, fft_buffer);
      arm_cmplx_mag_f32(fft_buffer, fft_buffer, FFT_SIZE/2);
      for (int i = 0; i < FFT_SIZE/2; i++) {
        float32_t mag = fft_buffer[i];
        float32_t db = 20 * log10(mag) - 20 * log10(32768.0);
        // do something with db
      }
    }
  }
}

int main(void)
{
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
  GPIO_InitTypeDef GPIO_InitStructure;
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
  GPIO_Init(GPIOA, &GPIO_InitStructure);

  ADC_Configuration();
  FFT_Configuration();

  while (1) {
  }
}

其中，ADC_Configuration()函数配置ADC和DMA模块，FFT_Configuration()函数配置FFT模块和计算分贝值的代码。在计算分贝值时，需要将FFT的模值转换为分贝值，公式为：dB = 20 * log10(mag) - 20 * log10(32768)，其中mag为FFT的模值，32768为量化的最大幅度值，即2的15次方。