ADLINK Technology cPCI-7300A, User Manual

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40 Operation Theory
4.6 Scatter/gather DMA
The PCI Bridge also supports the function of scatter/gather bus
mastering DMA, which helps the users to transfer a large amount
of data by linking the all memory blocks into a continuous linked
list.
In the multi-user or multi-tasking OS, like Microsoft Windows,
Linux, and so on. It is difficult to allocate a large continuous mem-
ory block to do the DMA transfer. Therefore, the PLX PCI-9080
provides the function of scatter/gather or chaining mode DMA to
link the non-continuous memory blocks into a linked list so that
users can transfer a very large amount of data without limiting by
the fragment of small size memory. Users can configure the linked
list for the input DMA channel or the output DMA channel. Figure
4-7 shows the linked list that is constructed by three DMA descrip-
tors. Each descriptor contains a PCI address, a local address, a
transfer size, and the pointer to the next descriptor. Users can allo-
cate many small size memory blocks and chain their associative
DMA descriptors altogether by their application programs. The
cPCI/PCI/PCIe-7300A’s software driver provides the easy settings
of the scatter/gather function, and some sample programs are also
provided within the ADLINK all-in-one CD. Users can refer to
these sample programs and the function 5.14 and 5.18 for more
detailed description.
Figure 4-5: Scatter/gather DMA for digital output
PCI/PCI Express Bus