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bus controller provides DMA transfer with scatter-gather function to link non-contiguous
memory blocks into a linked list to enable transfer of large amounts of data without
memory limitations. In non-scatter-gather mode, the maximum DMA data transfer size is
2 MB double words (8 MB bytes); in scatter-gather mode, there is no limitation on DMA
data transfer size except the physical storage capacity of the system. Users can also link
descriptor nodes circularly to achieve a multibuffered DMA. A linked list comprising three
DMA descriptors. Each descriptor contains a PCI address, PCI dual address, a transfer size,
and the pointer to the next descriptor.PCI address and PCI dual address support 64-bit
addresses which can be mapped into more than 4 GB of address space, as shown.
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Figure 3-2: Linked List of PCI Address DMA Descriptors
