User manual

Chapter 7 VXIplug&play for the VXI-MXI-2

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

VXIbus mainframe with only one master of the entire system—VXIbus

and MXIbus. This mode of operation prevents deadlocks by

interlocking all arbitration in the VXIbus/MXIbus system.

The options for this control are Enabled and Disabled. By default, this

option is disabled, which puts the VXI-MXI-2 in normal operating

mode.

In normal operating mode (non-interlocked), multiple masters can

operate simultaneously in the VXIbus/MXIbus system. A deadlock

occurs when a MXIbus master requests use of a VXIbus resource in

another VXIbus mainframe while a VXIbus master in that mainframe is

in the process of requesting a resource across the MXIbus. When this

situation occurs, the VXIbus master must give up its bus ownership to

resolve the conflict. The RETRY signal is used to terminate the transfer

on the VXIbus; however, devices in the VXIbus 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-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 VXIbus modules in your system do not

have the capability for handling RETRY conditions, you may want to

configure the VXI-MXI-2 for interlocked arbitration mode. In this

mode, no software provisions for deadlock conditions are required.

However, parallel processing in separate VXIbus mainframes is no

longer possible, and system performance may be lower than in normal

operating mode.

In a VXIbus/MXIbus system, you can configure some VXI-MXI-2

modules for normal operating mode and others for interlocked

arbitration mode. The VXIbus 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.