Chapter
6 NI-VXI
Configuration
Utility
©
National Instruments Corporation
6-21
VXI/VME-MXI-2 itself via its requested memory space from both the
VXI/VMEbus and the MXIbus. For more information on the A16, A24, and
A32 windows, refer to VXI-6, the
VXIbus Mainframe Extender
Specification
.
Interlocked Mode
Interlocked arbitration mode is an optional mode of operation in which at
any given moment the system can perform as if it were one large
VXI/VMEbus mainframe with only one master of the entire
system—VXI/VMEbus and MXIbus. This mode of operation prevents
deadlocks by interlocking all arbitration in the VXI/VMEbus/MXIbus
system. By default, this option is disabled, which puts the
VXI/VME-MXI-2 in normal operating mode.
In normal operating mode (non-interlocked), multiple masters can operate
simultaneously in the VXI/VMEbus/MXIbus system. A deadlock occurs
when a MXIbus master requests use of a VXI/VMEbus resource in another
VXI/VMEbus mainframe while a VXI/VMEbus master in that mainframe
is in the process of requesting a resource across the MXIbus. When this
situation occurs, the VXI/VMEbus master must give up its bus ownership
to resolve the conflict. The
RETRY
signal is used to terminate the transfer
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 clicking on the Enable checkbox. 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.
