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Chapter 6
NI-VXI Configuration Utility
VXI/VME-PCI8026 for Linux
Normally, when a cycle maps from the MXIbus to the VXI/VMEbus, any
retry response received on the VXI/VMEbus is passed to the MXIbus. If
you enable the Auto Retry feature, the VXI/VME-MXI-2 automatically
retries any VXI/VME cycle that receives a retry response instead of passing
a retry response on to the MXIbus. The VXI/VME-MXI-2 automatically
continues to retry the VXI/VME cycle until it receives either a DTACK or
BERR response, which it then passes to the MXIbus.
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
MXIbus 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 MXIbus before releasing it to
another master device that is requesting use of the bus. The default setting
holds the MXIbus for an unlimited period of time.
The other options you can choose from are 16, 64, and 256 transfers. If you
do not want the VXI/VME-MXI-2 to hold the MXIbus for an unlimited
period of time, you can use this option to select one of these values.
Parity Checking
By default, MXIbus parity checking is enabled and should not be disabled
under normal circumstances. MXIbus parity is always generated regardless
if checking is enabled or disabled.
MXI Fair Requester
You can use the Operate as Fair Requester option to configure the
VXI/VME-MXI-2 as either a fair or unfair requester on the MXIbus. In its
default setting (disabled), the VXI/VME-MXI-2 will request the bus at any
time. If you enable this option, the VXI/VME-MXI-2 will request the
MXIbus only when there are no requests pending from other MXIbus
masters. This prevents other MXIbus masters from being starved of
bandwidth.
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