Jumpy touch pad observation
Gary C Martin
gary at garycmartin.com
Fri Jul 11 14:43:33 EDT 2008
On 11 Jul 2008, at 06:06, Richard A. Smith wrote:
> Gary C Martin wrote:
>> Forgive me if I'm about to start an old wives tale, but I've
>> encountered the jumpy touch pad issues quite a lot on the B4 XO I
>> have here for testing. I'm currently running a recent joyride
>> (2137) and firmware (Q2D16) and am still encountering issues.
>> Observation: If the XO is fully charged and still plugged in to
>> mains supply the jumpiness can be very persistent, however if I
>> unplug the power adapter, the XO seems to then correctly re-
>> calibrate within seconds.
> Its ground plane changes. According to Alps we are supposed to be
> issuing a recal on AC insert/removal or and lid open. And we don't
> do that yet in the chain of events.
> A claim from Alps is that there is so little metal in the XO that
> the ground plane capacitance has a really large variance based on
> its environment and whats plugged up to it. Even after we added
> more metal in the frame to help. So your observation falls in line
> with known data from the mfg.
Thanks, that information make me feel a little more sane for bringing
this up :-)
> If you are plugged up to mains and its jumpy does a 4 finger recal
> fix it?
Usually not... Let me clarify. There seem to be multiple causes of
jumpiness, some of which are fixed just fine by the 4 finger salute.
The really frustrating sessions are when the 4 finger salute makes no
difference, for the last month or two I've tried to vary my XO use so
that I use it both on and off mains power. If the touch pad looses
calibration and won't re-calibrate, it's is _usually_ when I am still
plugged into mains and with a full battery charge – unplugging the AC
and waiting a moment or two usually resolves the persistent failed re-
With the latest Joyride changes, it seems much clearer/easier to see
when the driver is trying to re-calibrate as the pointer suddenly
stops moving for a few seconds. In the persistent case (plugged in &
charged), leaving the touch pad alone to allow calibration to complete
usually does not work, and the cursor continues to jump (or float when
your finger is near but not touching the surface) when you try to use
it again. Unplug the AC, and the auto re-calibration usually
> Either way when its jumpy please enable kern.* logging in /etc/
> rsyslog.conf, route it to a file, and restart rsyslogd. Then echo 1
> > /sys/module/psmouse/parameters/tpdebug
> Then use the mouse jumpy for a while and send me, dilinger, or
> deepak the log file for us to look at.
OK, will do. Thanks for you feedback.
 The common case seems to be touching the pad in two places in
quick succession, this is easily done when trying to use the left or
right mouse buttons while moving the pointer as they are placed so
near the touch surface. I often hit this when using the drag metaphor
(probably what makes arranging activities on the new random home
screen layout feel more frustrating than it should be).
 I think the cases I've seen where it does not succeed are down to
damp hands, greasy/wet smear somewhere on pad, perhaps nylon
underpants (I'm joking!)
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