PDM2PCM转换结果成了脉冲波形，请大神指点

scanli 提问时间：2018-10-24 11:08 /

问答
是否解决:

1.环境：

         stm32f407vet6

         SPI2作为PDM麦克数据的输入，
         单路数字mic，MIC的L/R管脚接地，

         SPI2的时钟为1.28MHz。
2.配置：SPI2的配置：
/* SPI2 init function */
static void MX_SPI2_Init(void)
{

  /* SPI2 parameter configuration*/
  hspi2.Instance = SPI2;
  hspi2.Init.Mode = SPI_MODE_MASTER;
  hspi2.Init.Direction = SPI_DIRECTION_2LINES_RXONLY;
  hspi2.Init.DataSize = SPI_DATASIZE_16BIT;
  hspi2.Init.CLKPolarity = SPI_POLARITY_LOW;
  hspi2.Init.CLKPhase = SPI_PHASE_1EDGE;
  hspi2.Init.NSS = SPI_NSS_SOFT;
  hspi2.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_32;
  hspi2.Init.FirstBit = SPI_FIRSTBIT_MSB;
  hspi2.Init.TIMode = SPI_TIMODE_DISABLE;
  hspi2.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
  hspi2.Init.CRCPolynomial = 10;
  if (HAL_SPI_Init(&hspi2) != HAL_OK)
  {
_Error_Handler(__FILE__, __LINE__);
  }

}

PDM2PCM配置：

void MX_PDM2PCM_Init(void)
{
  PDM1_filter_handler.bit_order = PDM_FILTER_BIT_ORDER_LSB;
  PDM1_filter_handler.endianness = PDM_FILTER_ENDIANNESS_LE;
  PDM1_filter_handler.high_pass_tap = 1932735282;
  PDM1_filter_handler.in_ptr_channels = 1;
  PDM1_filter_handler.out_ptr_channels = 1;
  PDM_Filter_Init(&PDM1_filter_handler);

  PDM1_filter_config.decimation_factor = PDM_FILTER_DEC_FACTOR_80;
  PDM1_filter_config.output_samples_number = 16;
  PDM1_filter_config.mic_gain = 0;
  PDM_Filter_setConfig(&PDM1_filter_handler, &PDM1_filter_config);
}
PDM2PCM转换
uint8_t MX_PDM2PCM_Process(uint16_t *PDMBuf, uint16_t *PCMBuf)
{
   uint32_t retuVal;
   retuVal= PDM_Filter(PDMBuf,PCMBuf,&PDM1_filter_handler);
   return retuVal;
}

3.数据处理：  PDM2PCM
#define PDMBUFSIZE          160    //16bit
#define PCMBUFSIZE          16          //16bit
#define PCM2DACBUFSIZE       60       //16bit

void HAL_SPI_RxCpltCallback(SPI_HandleTypeDef *hspi)
{
uint8_t i;
uint16_t  tmpPDM[PDMBUFSIZE/2];
if(hspi==&hspi2)
{
      for(i=0;i<PDMBUFSIZE/2;i++)
         tmpPDM=HTONS(PDMDataBuf[i+PDMBUFSIZE/2]);
      PDM2PCMState=MX_PDM2PCM_Process(tmpPDM,PCMdataBuf);
      for(i=0;i<PCMBUFSIZE;i++)
      {
         if(PCM2DACBuf->isFull(PCM2DACBuf)==true)
         PCM2DACBuf->add(PCM2DACBuf, (PCMdataBuf+i)); ////写入DAC转换
         }

}
}

void HAL_SPI_RxHalfCpltCallback(SPI_HandleTypeDef *hspi)
{
  uint8_t i;
uint16_t  tmpPDM[PDMBUFSIZE/2];
if(hspi==&hspi2)
{
      for(i=0;i<PDMBUFSIZE/2;i++)
         tmpPDM=HTONS(PDMDataBuf);
      PDM2PCMState=MX_PDM2PCM_Process(tmpPDM,PCMdataBuf);

      for(i=0;i<PCMBUFSIZE;i++)
      {
            if(PCM2DACBuf->isFull(PCM2DACBuf)==true)
               PCMBufFullFlag++;
            PCM2DACBuf->add(PCM2DACBuf, (PCMdataBuf+i)); //写入DAC转换
         }
}
}
结果：  转换后的PCM数据只有两种情况：要么是接近0xffff,要么接近ox0000.也就是说，转换的输出成了类似PWM的脉冲，而不是正常音频的PCM数据。