New touchpad still has some jumpyness

Jim Gettys jg at
Tue Nov 25 20:56:44 EST 2008

On Tue, 2008-11-25 at 18:54 -0500, Richard A. Smith wrote:
> During SJ's demo meeting today at 1cc I used my test machine with the 
> new touchpad.
> The touchpad on my laptop is much deeper inset than
> I still experienced jumpyness.   However, a much different jumpyness 
> than what happens with the alps device.  In my case it appears to happen 
> if the tip of my thumb gets up into the active area. (Creepage from 
> using it to click thThe touchpad on my laptop is much deeper inset than 
> e X button)   What I saw was the cursor would leap to the edge of the 
> screen which is similar to what happens with the current pad, but unlike 
> the current pad its does not continue to leap around. It a one shot and 
> then returns to normal movement.  This happened to me several times.
> So then I played with my HP laptop which also has a synaptics touchpad 
> and I'm able to duplicate the same behavior.

It's worth a gander at the upstream synaptics driver; I've seen some
patches go by recently.

> So even with the new touchpad we still may have to have some sort of 
> criteria for discarding packets with large deltas for the movement.
> By default in mouse mode the values reported by the device are relative. 
>   So some sort of edge effect must confuse the controller.  I need to 
> enable some logging and see what data the device actually sent.
> I've also noticed that the acceleration of the new touchpad is much less 
> than the alps device.  When you switch from new to old the you can 
> really tell.  We should reduce the acceleration of the cursor for the 
> alps device. Its not necessary to be that fast.

Yeah, the acceleration stuff in X sucks.  Fixed in next release, IIRC
(after something like 20 years...)....

> Is that something we can set defaults for in the X config or do we have 
> to detect what touchpad we are running?

Unfortunately, we'll have to detect it.  This whole are of X is being
reworked as we speak....  Upstream, everything is hot plug, and you can
then set things on a per detected device basis.
                              - Jim

Jim Gettys <jg at>
One Laptop Per Child

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