[9fans] vmware thinkpad t23 windows 2000 mouse problems

[9fans] vmware thinkpad t23 windows 2000 mouse problems

[Russ Cox]

[This is for the archives, since as far as I know I am the only
one that experienced this problem.  But I expect more people will in the
future.]

On my T23 using Windows 2000 as host, VMware does not deliver
middle mouse events to its guest operating systems unless you
disable the trackpoint controller and use an external mouse.
Eventually I tracked this to the DirectInput (DirectX) driver API not
delivering middle mouse events to its clients.

The ultimate culprit on the software side is the Windows-supplied
PS/2 mouse driver i8042prt.sys, on top of which all the custom
PS/2 mouse drivers sit.

The Windows driver expects the Trackpoint to respond to command E9
as the Logitech mice do, giving the number of buttons as the second byte.
Unfortunately, the Trackpoint sends back some form of sampling resolution
instead, and even more unfortunately the default resolution is encoded
as 0x02, tricking Windows into thinking that there are but two mouse
buttons on the Trackpoint.  Since this is the Trackpoint controller simply
implementing a different command E9, the only way to get the hardware
to respond correctly is to turn it off in the BIOS, so that the external
mouse can respond for itself.

Happily, Windows is nothing if not configurable.  In the registry key

HKLM\SYSTEM\CurrentControlSet\Enum\ACPI\IBM3780\<uglyhexhere>\DeviceParameters

if you add a DWORD variable NumberOfButtons with value 3, Windows
will ignore what it has incorrectly interpreted the hardware to have said.
(I learned this reading the Windows 2000 i8042prt driver source.)

After that, VMware works fine: I get my middle button events.
Finally Plan 9 is usable.

Russ