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FreeBSD Device Drivers by Joseph Kong

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Chapter 12. Direct Memory Access

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Direct Memory Access (DMA) is a feature of modern processors that lets a device transfer data to and from main memory independently of the CPU. With DMA, the CPU merely initiates the data transfer (that is to say, it does not complete it), and then the device (or a separate DMA controller) actually moves the data. Because of this, DMA tends to provide higher system performance as the CPU is free to perform other tasks during the data transfer.

Note

There is some overhead in performing DMA. Accordingly, only devices that move large amounts of data (for example, storage devices) use DMA. You wouldn’t use DMA just to ...

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