Appendix B
Common Questions
PCI-Based MXI-2 Interfaces for Windows 2000/NT/Me/98
B-8
ni.com
What are the user and driver windows?
The PCI-MXI-2 and PXI-8320 driver requires the use of two PCI windows:
a user window and a driver window. NI-VXI uses the driver window to
perform high-level functions such as
viIn/Out()
or
VXIin/out()
and
to access registers on the MXI-2 boards in the system. The user window
is reserved for low-level function calls, such as
viPeek
/
Poke()
or
VXIpeek/poke()
, and
viMapAddress
or
MapVXIAddress()
. The
driver window is system defined and not configurable, but you can increase
the size of your user window through MAX if you expect to initiate
transfers to a wide variety of addresses in both A24 and A32 address space.
What is shared memory and dual-ported memory?
These terms refer to a block of memory that is accessible to both a client
and a server. The memory block operates as a message buffer for
communications. Shared memory is needed only if you have devices
capable of bus mastering in A24 or A32 space.
How should I assign logical addresses in a multiple-mainframe
system?
A simple algorithm for a system containing only one level of hierarchy—
a single chain of MXI cables—is to use the upper nibble (most significant
four bits) as a
frame
number and the lower nibble (least significant four
bits) as a
device
number. For example, the
fifth
device in the
third
mainframe would be logical address 35 (hex).
For more detailed information on this topic, refer to the
VXI-MXI-2 User
Manual
, the
VME-MXI-2 User Manual
, or
VXI-6, VXIbus Mainframe
Extender Specification
. You can also download the Logical Address
Wizard, a useful tool for determining logical address assignments, from
ni.com
.
