Mouse swapping on a laptop

[bscott at ntisys.com]

On Fri, 1 Aug 2003, at 2:34pm, mkomarinski at wayga.org wrote:
> Remember the PS/2 port is not hot-swap safe.

  Most laptops have electronics specifically designed to handle hotswap for
PS/2.  I won't say "all", but I'd be surprised to find one that did not.

  What's going on here is that the two different pointing devices (the
internal touch-pad and the external wheel-mouse) both connect via the same
logical PS/2 interface.  The laptop has logic to "multiplex" the two devices
together, so that both can send inputs to the same logical PS/2 interface.

  Now, the original PS/2 specification did not know about "wheels".  In
order to add support for wheels, various "extensions" to the original PS/2
protocol have been created.  These protocols are not quite compatible --
either with each other, or with the original "non-wheel"  PS/2 protocol.

  I suspect the problem Dan Coutu <coutu at snowy-owl.com> is seeing arises
because of this.  Somehow, a protocol mismatch is occurring.  The details
I'm not sure on, but I'm guessing it has to do with the fact that XFree has
been told to initialize and use a wheel mouse, when no wheel mouse is
present.

  Myself, I have solved this kind of problem in the way that Derek Martin
suggests.  There can be only one PS/2 "auxiliary" device, so the laptop's
electronics have to be responsible for multiplexing the PS/2 signals.  Not
so with USB.  By using only one pointer as a PS/2 pointer, and the rest as
USB pointers, the kernel and/or XFree can handle multiple inputs and
multiple protocols.

  I think Bill Mullen's idea of using multiple XFree configuration options
would also work, but the USB method (if the hardware allows for it) avoids
the need to specify X startup options.

-- 
Ben Scott <bscott at ntisys.com>
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