，DMA方式就是在一定时间段内，由DMA控制器取代CPU，获得总线控制权，来实现内存与外设或者内存的不同区域之间大量数据的快速传送。-, DMA mode is in a certain period of time, by the DMA controller to replace the CPU, access to the bus control, to achieve the memory and peripherals or memory large amounts of data b