Chapter 6 NI-VXI Configuration Utility
VXI/VME-PCI8022 for Solaris 6-22
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National Instruments Corporation
The A24/A32 write posting control affects write cycles that map
through the A24 window and A32 window from the VXI/VMEbus to
the MXIbus and vice-versa. This control also affects write cycles to the
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/ VME bus
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.