ADLINK PCI-7300A - Manual (Page 39)

Operation Theory
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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 memory 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. The figure 4.7 shows the linked list
that is constructed by three DMA descriptors. Each descriptor contains a PCI
address, a local address, a transfer size, and the pointer to the next descriptor.
Users can allocate many small size memory blocks and chain their associative
DMA descriptors altogether by their application programs. The
cPCI/PCI-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 4.7: Scatter/gather DMA for digital output