Chapter 4 Developing Your Application
© National Instruments Corporation 4-7 NI VXIpc-882 User Manual
Note 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 help for information regarding these options.
Optimizing Large VXIbus Transfers
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 are capable of accepting block transfers.
• To optimize move performance on virtual memory systems, 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, use a
contiguous buffer so the move operation does not need to build a
scatter-gather list for the user buffer.
Note viMemAlloc() or VXImemAlloc() returns 32-bit aligned, page-locked,
contiguous buffers which work efficiently with the move operations.
Table 4-1. NI-VISA/NI-VXI Examples
Coverage NI-VISA Example
NI-VXI Example
(Optional)
Message-Based
Access
RdWrt.c VXIws.c
High-Level
Register Access
HighReg.c VXIhigh.c
Low-Level
Register Access
LowReg.c VXIlow.c
Sharing Memory ShareSys.c VXImem.c
Interrupt Handling AsyncIntr.c and
WaitIntr.c
VXIint.c
Trigger Handling WaitTrig.c VXItrig.c