What are the Minimum Data Transfer Sizes of the NI 6533 and 6534?Hardware: Digital I/O (DIO)>>High-Speed>>PCI-6534, Digital I/O (DIO)>>High-Speed>>PXI-6534, Digital I/O (DIO)>>High-Speed>>PCI-6533, Digital I/O (DIO)>>High-Speed>>PXI-6533
Problem: I am trying to transfer data between the card and the computer and the transfer occurs after trying to send a few data sets. What is the minimum transfer size and what can I do to transfer data in smaller amounts? Solution: The issue of a minimum transfer size pertains the the devices when they are operating with DMA (Direct memory Access) transfers. The NI 6533 and 6534 each have a predefined transfer size for DMA in order to improve efficiency at high data rates. The DMA transfer passes data between the card's FIFO buffer and computer's memory directly without needed to use the processor. The data transfer will occur when enough data has built up in either the card's FIFO or computer's memory to satisfy the minimum transfer size requirement for the device. The DMA transfers are enabled for the devices by default and can be changed using a DAQmx Channel property node or with the Set DAQ Device Information.vi for Traditional NI-DAQ. To avoid the issue of a minimum transfer size, change the data transfer mechanism to be Interrupts. Using interrupts, you will ask the processor on the computer to handle the data transfer, but this will occur regardless of the amount of data available to transfer. This process is less efficient than a DMA transfer, so the maximum transfer rate will drop based on how quickly the processor can handle the interrupt requests and how quickly the data can be written to and from memory. Minimum DMA transfer size
The number of reads or writes that must occur in order to transfer data will depend on the sample size of your data set. For example, 16 bit reads on a PCI-6533 with DMA enabled will require that 2 reads occur on the device before data is transferred and the same 16 bit reads on a PCI-6534 with DMA enabled will require that 16 reads occur on the device to transfer data. This issue does not pertain to the NI 6535, 6536, and 6537. These devices only support DMA transfers, but do not have a minimum transfer size. Related Links: Product Manuals: NI 6533 and 6534 User Manual for Traditional NI-DAQ KnowledgeBase 298CGF9M: How Many Samples of Data Can I Store in the Onboard Memory of the NI 6533 and 6534? KnowledgeBase 34FGAFVM: How do I Configure the Data Transfer Mechanism (Interrupt or DMA) in DAQmx and Traditional DAQ? Attachments:
Report Date: 10/28/2004 Last Updated: 10/22/2008 Document ID: 3ERAA1TY |
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