Chapter 3
VXI Configuration Utility
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ni.com
VXI/VME Transfer Limit
You can use this feature to control how many data transfers the
VXI/VME-MXI-2 will perform on the VXI/VMEbus before releasing it to
another master device that is requesting use of the bus.
You can choose 16, 64, or 256 transfers. If you do not want the
VXI/VME-MXI-2 to hold the VXI/VMEbus long enough to perform
256 transfers (the default value), select a smaller value for this field.
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 field 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. If you select
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.
Arbiter Timeout
An arbitration timeout feature is available on the VXI/VME-MXI-2 when
it is acting as the VMEbus arbiter. This feature applies only to a VXI Slot 0
(VMEbus System Controller) VXI/VME-MXI-2. By default, this option is
enabled.
The timer begins when the arbiter circuit on the VXI/VME-MXI-2 drives
one of the
BGOUT
lines on the backplane. If no device takes over the bus
within the timeout limit, the
BGOUT
is removed and the bus is either idle
or granted to another requester.
Request Level
The VXI/VME-MXI-2 uses one of the four VMEbus request levels
(0 to 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.
