Touch-pad expectations

Richard A. Smith richard at
Mon Feb 7 02:11:43 EST 2011

On 02/04/2011 10:15 PM, Hal Murray wrote:
> Frequently, I find the touch-pad on a XO-1 to be extremely frustrating to use
> on cursor intensive tasks.  I'm trying to figure out if this is something I
> should be screaming and shouting about (and rubbing it in your collective
> noses) or if I should shut up and get used to it.

Basically the  CL1 XO-1 touchpad has hardware quirks that have shown to 
be very difficult to detect and correct with software.  The best effort 
we have right now is the kernels in the 10.x builds with modifications 
from Paul Fox that try to be smart about when to reject data from the 
touchpad and when to try and issue a recalibrate.

There's always one more thing to try so feel free to look at that code 
and try to make it smarter/better.  If you search this list for messages 
with the word "touchpad" you can re-read all the stuff we have tried.

One absolute we know is that the touchpad hates multi-touches.  If you 
have more than 1 point of contact with the sensor then it will go 
bonkers.  Due to the button placement below the touchpad this is quite 
easy to do.  Its trivial to show that double touches throw the pad into 
a tailspin.  Other failure modes are harder to duplicate.

Currently, we have some feedback from the field that if you increase the 
spacing between your finger and the touchpad via some sort of tape or 
sticker that it behaves much better.

Although nobody has provided a conclusive study on its benefits this 
hardware tweak is very plausible.  It is correct that if you increase 
the distance from your finger to the sensor that the sensitivity of the 
touchpad decreases.  If the "badness" of the touchpad is related to 
sensitivity then this will indeed make a difference.  More study is 
needed but some deployments are swearing by it.

Richard A. Smith  <richard at>
One Laptop per Child

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