The definition of DMA

The definition of DMA is a specialized processor (special purpose processor) that is useful to avoid loading the main CPU by a program I / O (PIO).

DMA Block Diagram

To start a DMA transfer, the host will write a DMA command block that contains a pointer to the source of the transfer, a pointer to the destination / transfer destination, and the number of bytes transferred, into memory. CPU then writes the address of this block command to the DMA controller, so the DMA controller can then operate the memory bus directly by placing the addresses on the bus to do the transfer without CPU assistance.



Processors prepared to provide a DMA transfer my data from the device, the operation will be displayed, the memory address of the source and destination data, and the number of bytes transferred.
DMA controller to start the operation (setting up a bus, provide the address, write and read data), until the entire block has been transferred.
DMA controller to interrupt the processor, where further action will be determined next.


The first method is a method that is very raw and simple called HALT, or Burst Mode DMA, because the DMA controller in control of the bus system and transfer all the blocks of data to or from memory on a single burst. While the transfer is still in progress, microprocessor system set idle, do not perform surgery to maintain an internal instruction register. This type of DMA operation like this exist on most computers.



Handshaking process between the DMA controller and device controller is done through a pair of wires called DMA and DMA-request-acknowledge. Device controller sends a signal via the DMA-request when it will transfer data as much as one word. This in turn will lead to the DMA controller to enter the addresses of the chill to the cable memory address, and send signals via cable DMA-acknowledge. After the signal via cable DMA-acknowledge is received, device controller sends the data in question and turn off the DMA-request signal