User`s guide

116 Agilent VISA User’s Guide
4 Programming via GPIB and VXI
• viPeek/viPoke calls do not return status codes.
• 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.