Debouncing the touch panel

The A5 touch panel produces touch events at /dev/input/touchscreen0, assuming you're using udev. Unfortunately, it produces events in a deluge whenever the pointer is anywhere near the screen. Most X applications cope well enough with a torrent of motion and proximity events, but the torrent of button events is a bigger problem. Essentially, anything that expects screen taps is likely to have a problem.

A quick-and-dirty fix can be implemented in the tslib input driver. In the Angstrom source distribution this is in the package `xf86-input-tslib'.

At around line 177 in tslib.c, change:

               xf86PostButtonEvent(local->dev, TRUE,
                        1, !!samp.pressure, 0, 2,
                        priv->lastx,
                        priv->lasty);

To

       long t = samp.tv.tv_usec + samp.tv.tv_sec * 1000000;
         if (t - lastButton > buttonIntervalUsec || !samp.pressure)
           {
                xf86PostButtonEvent(local->dev, TRUE,
                        1, !!samp.pressure, 0, 2,
                        priv->lastx,
                        priv->lasty);
           }
         lastButton = t;

and add at the top:

long lastButton = 0;
long buttonIntervalUsec = 100000;

The effect of this change is to ignore all button-down events that are less that buttonInternalUsec microseconds apart.

This is a very crude fix but I've found it to work reasonably well in practice.