看不懂：“DMA_DeInit(UART3_TX_DMA);”的位置

发布于 2011-01-20 10:47:18 浏览：5464 订阅该版

对串口3的DMA设置，一般是凡在最前边；不知道放在这里有什么好处，不是把前面的设置冲掉了吗？
```static void DMA_Configuration(void)
{
#if defined (RT_USING_UART3)
	DMA_InitTypeDef DMA_InitStructure;

/* fill init structure */
	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_Normal;
	DMA_InitStructure.DMA_Priority = DMA_Priority_VeryHigh;       
	DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;

/* DMA1 Channel5 (triggered by USART3 Tx event) Config */
	DMA_DeInit(UART3_TX_DMA);                                     //这个位置?  
	DMA_InitStructure.DMA_PeripheralBaseAddr = USART3_DR_Base;
	DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;
	DMA_InitStructure.DMA_MemoryBaseAddr = (u32)0;     //?
	DMA_InitStructure.DMA_BufferSize = 0;
	DMA_Init(UART3_TX_DMA, &DMA_InitStructure);
	DMA_ITConfig(UART3_TX_DMA, DMA_IT_TC | DMA_IT_TE, ENABLE);
	DMA_ClearFlag(DMA1_FLAG_TC5);
#endif
}```

另外 (u32)0 怎么理解？
谢谢！