Chapter 6
NI-VXI Configuration Utility
©
National Instruments Corporation
6-15
VXI/VME Auto Retry
The VXI/VME-MXI-2 has an automatic retry feature for cycles that map
from the VXI/VMEbus to the MXIbus. By default this option is disabled.
Normally, when a cycle maps from the VXI/VMEbus to the MXIbus, any
retry response received on the MXIbus is passed to the VXI/VMEbus. If
you enable the Auto Retry feature, the VXI/VME-MXI-2 automatically
retries any MXI cycle that receives a retry response instead of passing a
retry response back to the VXI/VMEbus. The VXI/VME-MXI-2
automatically continues to retry the MXI cycle until it receives either a
DTACK or BERR response, which it then passes to the VXI/VMEbus.
Notice that the VXI/VME-MXI-2 has a limit on the number of automatic
retries it will perform on any one cycle. If the limit is exceeded and the
VXI/VME-MXI-2 receives another retry, it will pass a retry back to the
VXI/VMEbus even though Auto Retry is enabled.
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.
The available options you can choose from are 16, 64, and 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), you can use this option
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 option 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.
