Mxibus Fairness Option; Figure 3-14. Mxibus Fair Requester Selection - National Instruments VXI-MXI User Manual

Chapter 3 Configuration and Installation

MXIbus Fairness Option

The MXIbus fairness feature ensures that all requesting devices will be granted use of the
MXIbus. This feature prevents a high priority MXIbus device from consuming all of the
MXIbus bandwidth. If MXIbus fairness is enabled, a MXIbus master will not request the bus
until it detects that no other devices are requesting the bus. MXIbus fairness ensures that all
MXIbus masters have an equal opportunity to use the MXIbus.
The VXI-MXI factory default setting has the MXIbus fairness feature disabled. Keep this option
disabled if a device in your mainframe needs a large portion of the MXIbus bandwidth without
interruptions from lower priority requesters. In an unfair system, the order in which you connect
the MXIbus devices in the daisy-chain determines the priority of each device's MXIbus request.
MXIbus requesters closer to the MXIbus System Controller have higher priority than those
further down the MXIbus chain. The MXIbus fairness feature is controlled by the Fairness slide
switch. If you want your VXI-MXI to be a fair requester, change the slide switch from the
Disabled setting to Enabled, as shown in Figure 3-14.
Fairness Enabled
Fairness Enabled
S2
S2
Disabled Disabled
a. Fairness Disabled
b. Fairness Enabled
(Default Setting)

Figure 3-14. MXIbus Fair Requester Selection

© National Instruments Corporation 3-17 VXI-MXI User Manual