ADLINK PCIe-9529 - Manual (Page 31)

Operations 21
PCIe-9529
ing OS, such as Microsoft Windows, Linux, or other, it is difficult to
allocate a large continuous memory block. Therefore, the bus con-
troller 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.
Figure 3-2: Linked List of PCI Address DMA Descriptors
First PCI Address PCI Address PCI Address
Local Memory
(FIFO)
PCI Bus
First Dual Address Dual Address
Transfer Size
Next Descriptor
Transfer Size
Next Descriptor
Dual Address
Transfer Size
Next Descriptor