DMA and DMA controller

1. Perspective View Introduction to the DMA and DMA controller. Need of DMA and DMA controller. Working of the DMA and DMA controller.

2. What is DMA ? DMA represents the DIRECT MEMORY ACCESS . Means there is a direct way to access the memory not by the help of other device. DMA is a feature of computerized system that allows the certain hardware subsystems to access main memory independently of CPU. Introduction to DMA

3. Without DMA ,during input/output operation the whole CPU is occupied for read and write operation , and is thus unavailable to perform other work. With DMA , the CPU does the other operation while the transfer is in progress. DMA is used in intra-chip data transfer in multi-core processors and also used in disk drive , graphic cards, network cards and sound cards. Need of DMA

4. A DMA controller can generate memory addresses and initiate memory read or write cycles. It contains several processor registers that can be written and read by the CPU. The control registers specify the I/O port to use , the direction of the transfer and the number of bytes to transfer in one burst. Introduction to DMA Controller

5. Operation of DMA Controller An entire block of data is transferred in one contiguous sequence. Once the DMA controller is granted access to the system bus by the CPU, it transfers all bytes of data in the data block . Burst Mode Cycle Stealing mode The cycle stealing mode is used in systems in which the CPU should not be disabled for the length of time needed for burst transfer modes. In the Cycle stealing mode , the DMA controller obtains access to the system bus. Transparent mode The transparent mode takes the most time to transfer a block of data , yet it is also the most efficient mode in terms of overall System performance.

6. Peripheral to memory DMA operation Micro Processor Memory DMA Controller Peripheral Device Address bus Data bus Control bus Hold Ack Hold Request Data bus Control DMA Request DMA Ack

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