Mouse swapping on a laptop

[Mark Komarinski]

On Fri, Aug 01, 2003 at 02:21:07PM -0400, Dan Coutu wrote:
> Bill Freeman wrote:
> >Derek Martin writes:
> > > While again, I didn't spend much time on it, the problem with using a
> > > PS/2 mouse seems to be that Linux sees that and the internal mouse
> > > device as the same logical device (/dev/psaux), with the same
> > > configuration.  However, obviously that's not true in reality.  I know
> > > of no way to handle two different configurations on the same device...
> >
> >	I suspect that this is actually a BIOS issue.  Probably the
> >same hardware is used to interface the internal mouse and the PS/2
> >socket, with a wee bit of steering logic.  If I'm correct, at boot
> >time the BIOS "probes" for a mouse with the steering set for the
> >external connector, and if it finds none, flips the "switch", and
> >initializes the internal mouse.  So either mouse gets talked to by the
> >Linux kernel via the same hardware register set, and /dev/psaux is,
> >in fact, totally correct for both.
> >
> >	If the switching control bit is readable, you could
> >conceivably as a module to read it, and adjust the mouse configuration
> >accordingly.  That would be chip set, and maybe even brand/model
> >specific, however.  Another hope would be for the BIOS to provide a
> >callback interface to query the mouse choice.
> >
> >							Bill
> 
> Well in my case I can use both the external mouse and the touchpad at
> the same time. So clearly the BIOS is not switching one or the other
> into place.
> 
> The idea of plugging the external mouse into the USB port is worth 
> investigating though since this particular mouse can use either USB or 
> PS/2 port.

Remember the PS/2 port is not hot-swap safe.  Most modern machines have
fuses to prevent the circuits shorting out, but it can have consequences
like what you're seeing.  Using the USB port will allow you to plug
and unplug the mouse at will and be able to use the wheel.  There's
a change or two you would have to make to your X configuration to get
it to work.

-Mark
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