Chapter 6 NI-VXI Configuration Utility
PCI-MXI-2 for Linux 6-26 ni.com
enough to perform 256 transfers (the default value), you can use this control
to select a smaller value.
Arbiter Type
You can use the Arbiter Type feature to configure the VXI/VME-MXI-2
as either a Priority or Round Robin VMEbus arbiter. This control is
applicable only if the VXI/VME-MXI-2 you are configuring is a VMEbus
System Controller (VXI Slot 0) device. The default value is Priority.
When configured for Priority arbitration, the VXI/VME-MXI-2 grants the
bus to the highest pending bus request level. In Round Robin arbitration
mode, the VXI/VME-MXI-2 grants the bus to the next highest bus request
level after the level of the previous bus owner. This effectively gives the
same priority to each bus request level. Refer to the VMEbus specification
for more information on the different types of arbiters.
Request Level
The VXI/VME-MXI-2 uses one of the four VMEbus request levels
(0to 3)to request use of the VME Data Transfer Bus (DTB). The
VXI/VME-MXI-2 requests use of the DTB whenever an external MXIbus
device, such as a PCI-based computer with a PCI-MXI-2 interface,
attempts a transfer that maps into the VXI/VMEbus mainframe.
The VXI/VME-MXI-2 uses VMEbus request level3 by default, as required
by the VXIbus specification. This is suitablefor most VXIbus systems.
However, you can change the VXI/VME-MXI-2 to use any of the other
three request levels (0, 1, or2) by changing the setting of the Request
Level control. You may want to change request levels to change the priority
of the VXI/VME-MXI-2 request signal. For more information, refer to the
VMEbus specification.
VXI/VME Fair Requester
The VXI/VME-MXI-2 is always a Release On Request requester.
However, you can configure whether the VXI/VME-MXI-2 acts as either
a fair or unfair requester on the VXI/VMEbus. By default, the Operate as
Fair Requester checkbox is enabled, signifying a fair requester. For more
information on the different types of requesters, refer to the VMEbus
specification.