STM32F0 ADC DMA快速采集

STM32 ADC支持DMA 方式传输，可提高传输效率。

从stm32 cube的实例程序可以看到有如下初始化程序

  /* ### - 1 - Initialize ADC peripheral #################################### */
  /*
   *  Instance                  = ADC1.
   *  ClockPrescaler            = PCLK divided by 4.
   *  LowPowerAutoWait          = Disabled
   *  LowPowerAutoPowerOff      = Disabled
   *  Resolution                = 12 bit (increased to 16 bit with oversampler)
   *  ScanConvMode              = ADC_SCAN_ENABLE 
   *  DataAlign                 = Right
   *  ContinuousConvMode        = Enabled
   *  DiscontinuousConvMode     = Enabled
   *  ExternalTrigConv          = ADC_SOFTWARE_START
   *  ExternalTrigConvEdge      = None (Software start)
   *  EOCSelection              = End Of Conversion event
   *  DMAContinuousRequests     = ENABLE
   */

  AdcHandle.Instance = ADC1;
  
  AdcHandle.Init.ClockPrescaler        = ADC_CLOCK_SYNC_PCLK_DIV4;
  AdcHandle.Init.LowPowerAutoWait      = DISABLE;