dma技术解释（DMA technical explanation）.docVIP

dma技术解释（DMA technical explanation） DMAs English spelling is Direct Memory Access. In Chinese it means direct memory access. It is a data exchange mode that accesses data directly from memory without CPU. PIO mode data transmission between the hard disk and memory are controlled by CPU; and in the DMA mode, CPU only to the DMA controller DMA controller to send orders, let to deal with the number of data transfer is completed and then give CPU feedback, thus greatly reduce the CPU resource share. The difference between DMA mode and PIO model is that the DMA model does not rely too much on CPU, which can greatly save system resources, and the difference in speed between the two is not very obvious. It can be divided into Single-Word DMA DMA mode (single byte DMA) and Multi-Word DMA (multi byte DMA) two, the maximum transmission rate is only 16.6MB/s direct memory access which can achieve (DMA) controller is a unique system in the peripheral internal transfer data, it can be regarded as a kind of can a group of dedicated bus controller will connect the internal and external memory and peripherals each with DMA capability. It belongs to the peripheral because it is programmed to be transferred under the control of the processor. It is important to note that only peripherals with larger data traffic (kBps or higher) are required to support DMA capabilities, and typical examples of these applications include video, audio, and network interfaces. In general, the DMA controller will include an address bus, a data bus, and a control register. An efficient DMA controller will have the ability to access any of the resources it needs, without the intervention of the processor itself, it must be able to generate interrupts. Finally, it must be able to compute addresses within the controller. A processor can contain multiple DMA controllers. Each controller has multiple DMA channels, and a number of buses directly connected to the memory station (memory, bank) and peripherals, as