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3�6 Data Transfers
Since the maximum data throughput on the PCI/PXI-69846 (40MS/ s * 4 channels *2 Bytes/
channel = 320MB/s) is much higher than the 32bit/33MHz PCI-bus bandwidth, samples are
acquired into the onboard SDRAM memory before being transferred to the host computer.
Since the number of stored samples per acquisition is limited by the amount of on-board
memory, the PCI/PXI-69816/26/ 46 supports maximum 512MB in order to meet application
requirements.
Once all the data has been stored in the on-board memory, the data will be transferred to
the host computer’s memory through bus-mastering DMA.
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 PCI/
PXI-69816/26/46 provides the function of scatter-gather DMA to link the non-continuous
memory blocks into a linked list so that you can transfer very large amounts of data without
being limited by the fragment of small size memory, as illustrated in Figure 3-17.
Figure 3-17: Scatter-Gather DMA for Data Transfer
