Chapter 6
NI-VXI Configuration Utility
©
National Instruments Corporation
6-13
on the VMEbus; however, devices in the VXI/VMEbus mainframe must be
able to detect a RETRY caused by a deadlock condition so that they can
retry the operation. Any master device that cannot detect the retry protocol
will interpret the response as a BERR signal instead.
The VXI/VME-MXI-2 is shipped from the factory configured for normal
operating mode (non-interlocked). If MXIbus transfers will be occurring
both into and out of the mainframe and the VXI/VMEbus modules in your
system do not have the capability for handling retry conditions, you may
want to configure the VXI/VME-MXI-2 for interlocked arbitration mode
by selecting the Enable option. In this mode, no software provisions for
deadlock conditions are required. However, parallel accesses in separate
VXI/VMEbus mainframes are no longer possible, and system performance
may be lower than in normal operating mode.
In a VXI/VMEbus/MXIbus system, you can configure some
VXI/VME-MXI-2 modules for normal operating mode and others for
interlocked arbitration mode. The VXI/VMEbus mainframes configured in
interlocked arbitration mode will be interlocked with each other and the
mainframes configured for normal operating mode can perform transfers in
parallel.
This type of system configuration is recommended if you have one of the
following situations:
•
A VXI/VMEbus mainframe with only slave devices and no masters.
Without bus masters, there is no chance for deadlock. You can
configure the VXI/VME-MXI-2 devices in this mainframe for normal
operating mode.
•
A VXI/VMEbus mainframe with both masters and slaves, but the
masters communicate only with the slaves in their mainframe. The
masters never attempt transfers across the MXIbus, so there is no
chance for deadlock when a MXIbus master attempts a transfer
into the VXI/VMEbus mainframe. You can configure the
VXI/VME-MXI-2 devices in this mainframe for normal
operating mode.
•
A VXI/VMEbus mainframe in which all masters that perform cycles
across the MXIbus support the VME64 RETRY protocol. You can
configure the VXI/VME-MXI-2 devices in this mainframe for normal
operating mode because all masters that could cause a deadlock will
automatically retry the operation.