Chapter 6
VXIplug&play for the VME-MXI-2
© National Instruments Corporation
6-5
VME-MXI-2 User Manual
The A16 Write Post control affects only write cycles that map through
the Extender A16 window from the VMEbus to the MXIbus and vice-
versa. A16 write cycles in VXI configuration space are never posted
regardless of the setting of this control.
The A24/A32 Write Post control affects write cycles that map through
the Extender A24 window and Extender A32 window from the
VMEbus to the MXIbus and vice-versa. This control also affects write
cycles to the VME-MXI-2 module via its requested memory space
from both the VMEbus and the MXIbus. For more information on the
A16, A24, and A32 windows, refer to Chapter 4, Register Descriptions.
Interlocked
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
VMEbus mainframe with only one master of the entire system—
VMEbus and MXIbus. This mode of operation prevents deadlocks by
interlocking all arbitration in the VMEbus/MXIbus system.
The options for this control are Enabled and Disabled. By default, this
option is disabled, which puts the VME-MXI-2 in normal operating
mode.
In normal operating mode (non-interlocked), multiple masters can
operate simultaneously in the VMEbus/MXIbus system. A deadlock
occurs when a MXIbus master requests use of a VMEbus resource in
another VMEbus mainframe while a VMEbus master in that mainframe
is in the process of requesting a resource across the MXIbus. When this
situation occurs, the 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 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 VME-MXI-2 is shipped from the factory configured for normal
operating mode. If MXIbus transfers will be occurring both into and
out of the mainframe, and the VMEbus modules in your system do not
have the capability for handling RETRY conditions, you may want to
configure the VME-MXI-2 for interlocked arbitration mode. In this
mode, no software provisions for deadlock conditions are required.
However, parallel processing in separate VMEbus mainframes is no
longer possible, and system performance may be lower than in normal
operating mode.
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