如题：STM32F446  ADC DMA模式下  经常OVR（数据溢出），导致ADC不工作。芯片STM32F446  ，系统时钟配置成168M，ADC为21M， 用PB0口进行ADC采样，软件触发方式，用DMA将采样数据存储在一个数组中。

程序跑着跑着ADC就停止工作，发现ADC_SR寄存器的OVR置为1，经过检查，也没查出有啥问题，请大神帮忙看看：
1、ADC配置如下
RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1, ENABLE);
ADC_DeInit();
ADC_CommonInitStructure.ADC_Mode = ADC_Mode_Independent;
ADC_CommonInitStructure.ADC_TwoSamplingDelay = ADC_TwoSamplingDelay_5Cycles;
ADC_CommonInitStructure.ADC_DMAAccessMode = ADC_DMAAccessMode_Disabled;
ADC_CommonInitStructure.ADC_Prescaler = ADC_Prescaler_Div4;//
ADC_CommonInit(&ADC_CommonInitStructure);

ADC_InitStructure.ADC_Resolution = ADC_Resolution_8b;
ADC_InitStructure.ADC_ScanConvMode = DISABLE;   
ADC_InitStructure.ADC_ContinuousConvMode = DISABLE;
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_8, 1, ADC_SampleTime_3Cycles);//ADC12_IN_8

    /* Enable DMA request after last transfer (Single-ADC mode) */
ADC_DMARequestAfterLastTransferCmd(ADC1, ENABLE);
    /* Enable ADC1 DMA */
ADC_DMACmd(ADC1, ENABLE);
ADC_Cmd(ADC1, ENABLE);

2、DMA配置如下
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA2, ENABLE);
  DMA_InitStructure.DMA_Channel = DMA_Channel_0;  
  DMA_InitStructure.DMA_PeripheralBaseAddr = (u32)&(ADC1->DR);
  DMA_InitStructure.DMA_Memory0BaseAddr = (u32)addr;
  DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory;
  DMA_InitStructure.DMA_BufferSize = len;
  DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
  DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
  DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;
  DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;
  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_Full;
  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);
  DMA_ITConfig(DMA2_Stream0, DMA_IT_TC, DISABLE);