The current debouncing code monitors events and switches on when events are
too close together. From then on, any event can be delayed.
Vicente Bergas provided an algorithm that avoids most of these delays:
on a button state change we now forward the change without delay but start a
timer. If the button changes state during that timer, the changes are
ignored. On timer expiry, events are sent to match the hardware state
with the client's view of the device. This is only done if needed.
Thus, a press-release sequence of: PRP sends a single press event, a sequence of
PRPR sends press and then the release at the end of the timeout. The timeout
is short enough that the delay should not be noticeable.
This new mode is called the 'bounce' mode. The old mode is now referred to as
'spurious' mode and only covers the case of a button held down that loses
contact. It works as before, monitoring a button for these spurious contact
losses and switching on. When on, button release events are delayed as before.
The whole button debouncing moves to a state machine which makes debugging a
lot easier. See the accompanying SVG for the diagram.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Some devices have worn-out switches or just cheap switches that trigger
multiple button events for each press. These can be identified by unfeasably
short time deltas between the release and the next press event. In the
recordings I've seen so far, that timeout is 8ms.
We have a two-stage behavior: by default, we do not delay any events but we
monitor timestamps. The first time a bouncing button is detected we switch to
debounce mode. From then on, release events are delayed slightly to check for
subsequent button events. If one occurs, the releas and press are filtered. If
none occurs, the release event is passed to the caller.
https://bugs.freedesktop.org/show_bug.cgi?id=100057
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
