JYTEK NuDAQ PCI-69222, User Manual

Page: 47 / 80

Operation Theory 37
The DMA transfer mode is a very complex to program. It is
recommended that you use a high-level program library provided
by the JYTEK driver to configure this card. By using a high-level
programming library for high speed DMA data acquisition, you
simply need to assign the sampling period and the number of
conversion through 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 scatter/gather bus mastering
DMA function that enables transfer of large amounts of data by
linking all the memory blocks into a continuous linked list.
In a multi-user or multitasking OS, like Windows, Linux, etc, it is
difficult to allocate a large continuous memory block to do the
DMA transfer. Therefore, the PCI controller provides the function
of scatter-gather or chaining mode DMA to link the non-continuous
memory blocks into a linked list, allowing transfers of very large
amounts of data without being limited by the fragment of small size
memory. You may configure the linked list for the input DMA
channel or the output DMA channel. Figure 4-8 shows a linked list that is
constructed by three DMA descriptors. Each descriptor contains a PCI
address, a PCI dual-address, a transfer size, and the pointer to the next
descriptor. PCI address and PCI dual-address support 64-bit addresses
which can be mapped into more than 4 GB of the address space. You can
allocate many small size memory blocks and chain their associative DMA
descriptors altogether by their application programs. The software
driver provides simple settings of the scatter-gather function, and some
sample programs are also provided at the www.jytek.com.