Strange bug with mouse wheel scrolling

Zephaniah E. Hull warp at
Tue Apr 11 13:41:59 PDT 2006

On Tue, Apr 11, 2006 at 02:50:23PM -0400, Greg Stark wrote:
> Matthias Hopf <mhopf at> writes:
> > On Mar 31, 06 00:00:55 -0500, Greg Stark wrote:
> > > I have a bug here but I'm not sure if it's an X bug or a Linux kernel bug or
> > > perhaps my mouse having some weird hardware failure, though it's never done it
> > > before. 
> > > 
> > > Whenever I scroll (vertically) by quickly spinning the mouse wheel it inserts
> > > the occasional horizontal scroll. Checking with xev it does in fact send the
> > > occasional "button 7" event:
> > 
> > See
> > 
> > I didn't have time so far to investigate this further, but your input
> > about your mouse model could help here.
> I'm not sure why it's in novell's bugzilla, should I register and comment
> there or just report it to x's bugzilla?
> That particular entry seems pretty enenlightening. It shows numerous people
> reporting the problem and nobody actually making any progress tracking down
> the source.
> In fact if I do cat -A /dev/input/mouse0 I see no unusual events. So I very
> much doubt this is a hardware issue.

Oh, joy, another one of these.

Under one variation of a ps2 mouse protocol with wheel, the byte used
for indicating wheel movement is just a signed byte which can show more
then just one step of movement in either direction.

For another common variation this is somewhat different, one value for
moved up one step, another for down one step, one for moving the second
wheel one step, another for moving the second wheel the other direction
one step..

For the first wheel's single step action the protocols are identical.

So, fix the protocol init and parsing to keep us talking the right
protocol and the problem should go away.

Zephaniah E. Hull.
(The guy who wishes he could reuse those neurons some days.  Ow, the

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