User`s guide

Programming via GPIB and VXI 4
Agilent VISA User’s Guide 101
• Only one active viMapAddress is allowed per vi session.
• There may be a limit to the number of simultaneous active
viMapAddress calls per process or system.
Using High-Level viIn/viOut
High-level viIn/viOut calls are best in situations where a few widely
scattered memory accesses are required and speed is not a major
consideration.
The advantages of high-level viIn/viOut are:
• It is the simplest method to implement.
• There is no limit on the number of active maps.
• A16, A24, and A32 memory access can be mixed in a single vi
session.
The disadvantage of high-level viIn/viOut calls is that they are slower
than viPeek/viPoke.
Using High-Level viMoveIn/viMoveOut
High-level viMoveIn/viMoveOut calls provide the highest possible
performance for transferring blocks of data to or from the VXI
backplane. Although these calls have higher initial overhead than the
viPeek/viPoke calls, they are optimized on each platform to provide the
fastest possible transfer rate for large blocks of data.
For small blocks, the overhead associated with viMoveIn/viMoveOut
may actually make these calls longer than an equivalent loop of
viIn/viOut calls. The block size at which viMoveIn/viMoveOut
becomes faster depends on the particular platform and processor speed.
The advantages of high-level viMoveIn/viMoveOut are:
• They are simple to use.
• There is no limit on number of active maps.
• A16, A24, and A32 memory access can be mixed in a single vi
session.
• They provide the best performance when transferring large blocks of
data.
• They support both block and FIFO mode.