Chapter 3
Developing Your Application
©
National Instruments Corporation
3-7
Address Space
The VXI-8340 series can decode any 32-bit address on the PCI bus as a
VXI cycle, giving 4 GB of addressability, which can be used for windows
on the VXI-8340 series. The operating system or computer architecture
may limit which addresses can be assigned to the VXI-8340 series.
To change the address space, edit the
User window size
field in the
PCI
tab of the VXI-8340 series
Hardware Configuration
settings in MAX.
This setting limits the total amount of memory you can map with
MapVXIAddress()
or
viMapAddress()
. If the User Window is disabled,
the
MapVXIAddress()
function returns
NO_HARDWARE_SUPPORT (-1)
.
The NI-VXI online help implies that the error code
MAP_TIMEOUT (-8)
is returned when the window is in use. Because the MITE-based products
have multiple hardware windows of variable size, the meaning of this
error has been modified.
MapVXIAddress()
now returns the error code
MAP_TIMEOUT (-8)
whenever there are not enough resources to map the
window.
For example, if you use
MapVXIAddressSize()
and
MapVXIAddress()
to request a 1 MB window to A32 space, and you request a User Window
in MAX of only 64 KB,
MapVXIAddress()
returns the error code
MAP_TIMEOUT
because there are not enough resources to complete the
request.
Number of MITE Windows
The MITE has eight CPU windows. NI-VXI uses four of these windows,
leaving four for user applications.
Memory for Allocating Data Structures
You need to have sufficient memory available for the operating system
to set up its necessary page tables. If you request a very large user
window—hundreds of megabytes, for example—you may run out of
memory.
MITE DMA
The MITE has two DMA channels to improve the throughput of block
transfers to and from the VXI system. The DMA channels can use various
high-speed bus protocols, such as the following:
•
Burst mode (on the PCI bus)
•
VME64 (on the VXI bus)