National Instruments VXI-USB User Manual

© National Instruments Corporation

MAX includes configuration options that affect low-level functions and shared 

memory, as well as trigger mappings and other attributes of your VXI system. Refer to the 
MAX online help for information regarding these options.

For best performance, keep the following in mind when using 

viMove()

 

or 

VXImove()

:

•

Make sure your buffers are 32-bit aligned.

•

Transfer 32-bit data whenever possible.

•

Use VXI block access privileges to significantly improve performance 
to devices that can accept block transfers, and likewise use D64 access 
privileges for devices that can accept the VME64 64-bit data transfer 
protocol.

•

To optimize move performance on virtual memory systems such as the 
Windows operating system, lock the user buffer in memory yourself so 
the move operation does not need to lock the buffer.

•

To optimize move performance on paged memory systems such as the 
Windows operating system, use a contiguous buffer so the move 
operation does not need to build a scatter-gather list for the user buffer.

viMemAlloc()

 or 

VXImemAlloc()

 returns 32-bit aligned, page-locked, 

continuous buffers that work efficiently with the move operations.

Table 3-1.  NI-VISA/NI-VXI Examples

Message-Based 
Access

General\RdWrt.c

VXIws.c

High-Level 
Register Access

VXI-VME\HighReg.c

VXIhigh.c

Low-Level Register 
Access

VXI-VME\LowReg.c

VXIlow.c

Interrupt Handling

VXI-VME\AsyncIntr.c

 

and 

WaitIntr.c

VXIint.c

Trigger Handling

VXI-VME\WaitTrig.c

VXItrig.c