User`s guide

38
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Operation Theory
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 continuous 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 scatter /gather functionality
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
21 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 descriptors altogether by their
application programs. DAQ-2213/2214 software driver provides simple
settings of the scatter/gather function, and some sample programs are also
provided in the ADLINK all-in-one CD.
Figure 21: Scatter/gather DMA for data transfer
In non-chaining mode, the maximum DMA data transfer size is 2M double
words (8M bytes). However, by using chaining mode, scatter/gather, there
is no limitation on DMA data transfer size. Users can also link the de-
scriptor nodes circularly to achieve a multi-buffered mode DMA.
4.2 D/A Conversion (for DAQ-2214 only)