Chapter 2
NI 5450 Overview
©
National Instruments Corporation
2-71
NI PXIe-5450 User Manual
PXI Express Bandwidth Considerations
National Instruments PXI Express signal generators use PCI Express as the
interface to the computer. The physical connection between a PXI Express
signal generator and a computer is called a
PCI Express link
. When a signal
generator generates a waveform, it can saturate this link. Saturation occurs
when the signal generator is copying data to its onboard memory from
computer memory as rapidly as possible, utilizing all of the bandwidth of
the PCI Express link.
The theoretical bandwidth of the onboard memory of the signal generator
is 3.2 GB/s, and the theoretical bandwidth of the PCIe link is approximately
850 MB/s. This difference in bandwidths means that transferring data to the
onboard memory can saturate the PCI Express link. The waveform data
download rate is dependent on the system configuration, with a maximum
of approximately 600 MB/s.
High-speed transfers that saturate the PCI Express link can affect other
devices when multiple devices share a single PCI Express link. For
example, if an NI PXI Express signal generator is installed in slot 9 of an
NI PXIe-1065 chassis controlled by an NI PXIe-8130 controller, the signal
generator will share bandwidth with any devices installed in Slots 10
through 14. This bandwidth sharing becomes a problem if other devices in
the application require guaranteed bandwidth to the PCI Express bus.
You can configure the NI PXI Express signal generator to limit its use of
the PCI Express bus, leaving bandwidth for other devices that are more
susceptible to short-term bursts of traffic on a shared PCI Express link. You
may also be able improve the performance of your device based on your
system configuration. The following table lists the properties and attributes
that allow you to modify the way that the signal generator uses the PXI
Express bus.
LabVIEW Property
C/C++ Attribute
Purpose
Maximum Bandwidth
NIFGEN_ATTR_DATA_TRANSFER
_MAXIMUM_BANDWIDTH
Allows you to optimize bus
bandwidth usage for multi-device
streaming applications.
