STM32F3为什么要使能 DMA_InitStructure.DMA_M2M = DMA_M2M_Enable才开始转换，不使能就不转换，程序是ADC到DMA

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    DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&ADC2->DR;
    DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)&adc2ConvertedValues;
    DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralSRC;
    DMA_InitStructure.DMA_BufferSize = 4;
    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_M2M = DMA_M2M_Enable;
    DMA_Init(DMA1_Channel2, &DMA_InitStructure);