Newsletters Archive - 2007

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  Erratic Mouse Behavior with Mouse on Linux and Belkin KVM Switch — (12-March-2007)

When using a Belkin KVM switch (and several others), you may notice erratic 
behavior with the PS/2 mouse when switching back and forth to a Linux machine 
running Red Hat Linux (and Mandrake 10). The PS/2 mouse will simply go nuts; 
jumping all around the screen with random button clicks when you try to move it 
anywhere! Often times, switching to a USB mouse will resolve the problem.

The root cause for this erratic behavior with the mouse rests in the fact that 
the PS/2 specification was not designed to be hot-pluggable. So, why is this a 
problem? Read on.

All PS/2 mice can work in what we will call "Basic PS/2 Mouse Mode"  no scroll 
wheel and only 2 or three buttons work. This is the default mode when the mouse 
initially gets power. To activate the scroll wheel and/or any extra buttons, 
the mouse must receive a special reset code. This switches the mouse to 
"Advanced Mouse Mode" and changes the mouse data protocol a little.

Many KVM switches may stop feeding power to the mouse when switching from one 
system to another. This causes the mouse to reset to "Basic PS/2 Mouse Mode". 
The system has no way of detecting that the mouse was reverted back to the 
basic mode. If the system was in a state where it had detected the mouse with 
"Advanced" capabilities and had sent it the appropriate reset code, it will 
expect the mouse to still be in "Advanced" mode and will misinterpret the mouse 
data (remember the mouse data protocol is different between Advanced and Basic 
mouse mode).

The following article provides several solutions that I have used to resolve 
this problem.

Erratic Mouse Behavior with Mouse on Linux and Belkin KVM Switch

Jeffrey M. Hunter
Sr. Database Administrator