ADLINK PXI-2006 - Manual (Page 51)

Operation Theory 41
please refer to http://www.plxtech.com for more in-formation on
PCI controllers.
By using a high-level programming library for high speed DMA
data ac-quisition, users simply need to assign the sampling
period and the number of conversion into their specified
counters. After the AD trigger condition is matched, the data
will be transferred to the system memory by the bus-mastering
DMA.
The PCI controller also supports the function of scatter/gather
bus mas-tering DMA, which helps the users to transfer large
amounts of data by linking all the memory blocks into a contin-
uous linked list.
In a 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 IOP-
480 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 very large amounts of data without
being limited by the fragment of small size memory. Users can
configure the linked list for the input DMA channel or the output
DMA channel. Figure 20 shows a 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 de-scriptors altogether
by their application programs. DAQ/PXI-20XX software driver
provides simple settings of the scatter/gather function, and
some sample programs are also provided within the ADLINK
all-in-one CD.