JYTEK PCIe-69834, Руководство пользователя

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16 Operations
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 multi-
buffered DMA. Figure 3-2 illustrates 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 descrip-
tor. PCI address and PCI dual address support 64-bit addresses
which can be mapped into more than 4 GB of address space, but
the subsequent descriptor address must be less than 4GB.
Figure 3-2: Linked List of PCI Address DMA Descriptors
Local Memory
( FIFO)
PCI Express Bus
First PCI Address
First Dual Address
Transfer Size
Next Descriptor
PCI Address
Dual Address
Transfer Size
Next Descriptor
PCI Address
Dual Address
Transfer Size
Next Descriptor