Strange bug with mouse wheel scrolling

Matthias Hopf mhopf at
Wed Apr 12 03:33:59 PDT 2006

On Apr 11, 06 16:41:59 -0400, Zephaniah E. Hull wrote:
> > 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..

Wow, this explains everything! Thanks, Zephaniah.
It's also clear why this didn't occur earlier, because the buttons for
horizontal wheels weren't mapped by default before.

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

Do you have information or pointers about how to detect the different
protocols? Appearantly something in the code isn't right, so I don't
want to read the code to find out...


Matthias Hopf <mhopf at>       __        __   __
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