ADC采样

ADC转换是指将输入的模拟量转化为数字量，并且将数字量读取出来。完成这个动作的时间叫做ADC的采样周期。

采样周期 =  转换时间+读取时间。转换时间 = 采样时间+12.5个周期。采样时间可以通过软件设置ADC采样时间寄存器来设置ADC的采样时间。对应的库函数如下：

/**
  * @brief  Configures for the selected ADC regular channel its corresponding
  *         rank in the sequencer and its sample time.
  * @param  ADCx: where x can be 1, 2 or 3 to select the ADC peripheral.
  * @param  ADC_Channel: the ADC channel to configure. 
  *   This parameter can be one of the following values:
  *     @arg ADC_Channel_0: ADC Channel0 selected
  *     @arg ADC_Channel_1: ADC Channel1 selected
  *     @arg ADC_Channel_2: ADC Channel2 selected
  *     @arg ADC_Channel_3: ADC Channel3 selected
  *     @arg ADC_Channel_4: ADC Channel4 selected
  *     @arg ADC_Channel_5: ADC Channel5 selected
  *     @arg ADC_Channel_6: ADC Channel6 selected
  *     @arg ADC_Channel_7: ADC Channel7 selected
  *     @arg ADC_Channel_8: ADC Channel8 selected
  *     @arg ADC_Channel_9: ADC Channel9 selected
  *     @arg ADC_Channel_10: ADC Channel10 selected
  *     @arg ADC_Channel_11: ADC Channel11 selected
  *     @arg ADC_Channel_12: ADC Channel12 selected
  *     @arg ADC_Channel_13: ADC Channel13 selected
  *     @arg ADC_Channel_14: ADC Channel14 selected
  *     @arg ADC_Channel_15: ADC Channel15 selected
  *     @arg ADC_Channel_16: ADC Channel16 selected
  *     @arg ADC_Channel_17: ADC Channel17 selected
  * @param  Rank: The rank in the regular group sequencer. This parameter must be between 1 to 16.
  * @param  ADC_SampleTime: The sample time value to be set for the selected channel. 
  *   This parameter can be one of the following values:
  *     @arg ADC_SampleTime_1Cycles5: Sample time equal to 1.5 cycles
  *     @arg ADC_SampleTime_7Cycles5: Sample time equal to 7.5 cycles
  *     @arg ADC_SampleTime_13Cycles5: Sample time equal to 13.5 cycles
  *     @arg ADC_SampleTime_28Cycles5: Sample time equal to 28.5 cycles	
  *     @arg ADC_SampleTime_41Cycles5: Sample time equal to 41.5 cycles	
  *     @arg ADC_SampleTime_55Cycles5: Sample time equal to 55.5 cycles	
  *     @arg ADC_SampleTime_71Cycles5: Sample time equal to 71.5 cycles	
  *     @arg ADC_SampleTime_239Cycles5: Sample time equal to 239.5 cycles	
  * @retval None
  */
void ADC_RegularChannelConfig(ADC_TypeDef* ADCx, uint8_t ADC_Channel, uint8_t Rank, uint8_t ADC_SampleTime)
{
  uint32_t tmpreg1 = 0, tmpreg2 = 0;
  /* Check the parameters */
  assert_param(IS_ADC_ALL_PERIPH(ADCx));
  assert_param(IS_ADC_CHANNEL(ADC_Channel));
  assert_param(IS_ADC_REGULAR_RANK(Rank));
  assert_param(IS_ADC_SAMPLE_TIME(ADC_SampleTime));
  /* if ADC_Channel_10 ... ADC_Channel_17 is selected */
  if (ADC_Channel > ADC_Channel_9)
  {
    /* Get the old register value */
    tmpreg1 = ADCx->SMPR1;
    /* Calculate the mask to clear */
    tmpreg2 = SMPR1_SMP_Set << (3 * (ADC_Channel - 10));
    /* Clear the old channel sample time */
    tmpreg1 &= ~tmpreg2;
    /* Calculate the mask to set */
    tmpreg2 = (uint32_t)ADC_SampleTime << (3 * (ADC_Channel - 10));
    /* Set the new channel sample time */
    tmpreg1 |= tmpreg2;
    /* Store the new register value */
    ADCx->SMPR1 = tmpreg1;
  }
  else /* ADC_Channel include in ADC_Channel_[0..9] */
  {
    /* Get the old register value */
    tmpreg1 = ADCx->SMPR2;
    /* Calculate the mask to clear */
    tmpreg2 = SMPR2_SMP_Set << (3 * ADC_Channel);
    /* Clear the old channel sample time */
    tmpreg1 &= ~tmpreg2;
    /* Calculate the mask to set */
    tmpreg2 = (uint32_t)ADC_SampleTime << (3 * ADC_Channel);
    /* Set the new channel sample time */
    tmpreg1 |= tmpreg2;
    /* Store the new register value */
    ADCx->SMPR2 = tmpreg1;
  }
  /* For Rank 1 to 6 */
  if (Rank < 7)
  {
    /* Get the old register value */
    tmpreg1 = ADCx->SQR3;
    /* Calculate the mask to clear */
    tmpreg2 = SQR3_SQ_Set << (5 * (Rank - 1));
    /* Clear the old SQx bits for the selected rank */
    tmpreg1 &= ~tmpreg2;
    /* Calculate the mask to set */
    tmpreg2 = (uint32_t)ADC_Channel << (5 * (Rank - 1));
    /* Set the SQx bits for the selected rank */
    tmpreg1 |= tmpreg2;
    /* Store the new register value */
    ADCx->SQR3 = tmpreg1;
  }
  /* For Rank 7 to 12 */
  else if (Rank < 13)
  {
    /* Get the old register value */
    tmpreg1 = ADCx->SQR2;
    /* Calculate the mask to clear */
    tmpreg2 = SQR2_SQ_Set << (5 * (Rank - 7));
    /* Clear the old SQx bits for the selected rank */
    tmpreg1 &= ~tmpreg2;
    /* Calculate the mask to set */
    tmpreg2 = (uint32_t)ADC_Channel << (5 * (Rank - 7));
    /* Set the SQx bits for the selected rank */
    tmpreg1 |= tmpreg2;
    /* Store the new register value */
    ADCx->SQR2 = tmpreg1;
  }
  /* For Rank 13 to 16 */
  else
  {
    /* Get the old register value */
    tmpreg1 = ADCx->SQR1;
    /* Calculate the mask to clear */
    tmpreg2 = SQR1_SQ_Set << (5 * (Rank - 13));
    /* Clear the old SQx bits for the selected rank */
    tmpreg1 &= ~tmpreg2;
    /* Calculate the mask to set */
    tmpreg2 = (uint32_t)ADC_Channel << (5 * (Rank - 13));
    /* Set the SQx bits for the selected rank */
    tmpreg1 |= tmpreg2;
    /* Store the new register value */
    ADCx->SQR1 = tmpreg1;
  }
}

 通道的采样时间会影响采样的精度。下面举例来进行说明：

例如ADCLCK = 14MHZ，设置 1.5周期的采样时间。那么 转换时间 = 1.5+12.5 =14周期 = 1us。

一般情况下，如果是软件启动，那么转换时间就是采样周期。

如果通过定时器进行触发启动ADC，则还需要加上定时器的相关时间。 

如果已知待采集的周期性信号的频率，怎样确定ADC的采样周期？

已知信号的频率为50hz（周期20ms），初步定一个周期采集2500个采样点，（一个周期最少要采集20个点，即采样率最少为1K），因此每两个点的采样间隔为20ms/2500 = 8us；如果ADC可编程通道的采样周期时间选择71.5周期，便可以知道ADC的时钟频率为9MHZ.、

 

ADC+DMA传输数据

  采用ADC+DMA的形式传输数据，遇到的问题：ADC正常采集数据，DMA不进入传输完成中断。经过以下调整解决问题。顺便总结ADC+DMA的配置方式

  1、配置DMA,

   

		DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&ADC1->DR;
		DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)ADC1_Value_buff; 
		DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralSRC;  // 内存作为数据传输的目的地址

 

 2、配置用于ADC采集数据的引脚；

 

 3、配置ADC。如果要采用DMA的方式一定要记得ADC_DMACmd(ADC1, ENABLE);这个地方坑了自己，开始配置时没有开启该DMA功能。

 4、在DMA传输完成中断完成时，要重新设置传输量的大小。