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----------------------------------------------
xf86-input-tc1kpen Pen Button events resolving
----------------------------------------------
As the implemented algorithm for button 3 emulaton
is quite complex (in meaning of compression of
semantics), I shall describe its derivation, here.
The HW mode is quite straightforward and doesn't
require closer explanation as well as the 3-button
extension to the following algorithm, I guess.
Emulating button 3 with pen tap while pen button pressed
--------------------------------------------------------
From now on, I shall use term button for both the pen tip
and pen button (they are both buttons in terms of functionality).
First, what happens upon a button press/release:
1/ If a button is pressed, 2 packets are sent to the serial
device:
i) STATUS bit set, BUTTON bit clear
ii) STATUS bit clear, BUTTON bit set
2/ From that moment, the BUTTON bit stays set until the
button is released. Then, 2 packets are sent. The first
of those may differ regarding current state of the other
button:
i) STATUS bit set, BUTTON bit clear if the other btn is released
BUTTON bit set if the other btn is pressed
ii) STATUS bit clear, BUTTON bit clear
The following image describes that:
PRESS RELEASE
V V
PACKET #: i i+1 j-1 j j+1
-------------------------------------~----------------------------------
1 +------+ +------+
| | | |
STAT bit: 0 -----+ +----------> ---+-----+ +------+------>
-------------------------------------~----------------------------------
Other btn. not pressed:
1 +------+---> ---+-----+
| |
BTN bit: 0 -----+------+ +------+------+------>
-------------------------------------~----------------------------------
Other btn. pressed:
1 +------+---> ---+-----+------+
| |
BTN bit: 0 -----+------+ +------+------>
-------------------------------------~----------------------------------
Now, assuming that we watch the STATUS bit changes,
this leads to the following algorithm:
+-------------------+
| STATUS bit change |
+---------+---------+
|
|
V
TRUE +-------------------+ FALSE
+----------+ STATUS bit set +-------+
| +-------------------+ |
| |
| |
V V
FALSE +---------------+ TRUE +---------------+ FALSE
X<--------+ button > 0 | +---------+ button > 0 +----+
+-------+-------+ | +---------------+ |
| TRUE | |
| | |
V V V
TRUE +----------------+ +----------------+ T F +----------------+
X<-------+ btn 1 bit set | | btn 1 bit set +--->X<---+ btn 1 bit set |
+--------+-------+ +--------+-------+ +--------+-------+
| FALSE | FALSE | TRUE
| | |
+--------------------+ V
| TRUE +----------------+
| +-----------+ btn 2 bit set |
V | +--------+-------+
+--------------------+ | | FALSE
| Release(button); | V V
| button = 0; | +-------------+ +----------------+
+----------+---------+ | button = 3; | | button = 1; |
| +--------+----+ +--------+-------+
| | |
V +--------------------+
X |
V
+-----------------+
| Press(button); |
+--------+--------+
|
V
X
('X' points mean exit).
The algorithm is obviously far from being efficient.
Minimalization follows:
The original algorithm in table form:
=============+==============+=============+=============+====================
STATUS bit | button > 0 | btn 1 bit | btn 2 bit | result
=============+==============+=============+=============+====================
0 | FALSE | 0 | 0 |
-------------+--------------+-------------+-------------+
0 | FALSE | 0 | 1 |
-------------+--------------+-------------+-------------+--------------------
0 | FALSE | 1 | 0 | Press(1)
-------------+--------------+-------------+-------------+--------------------
0 | FALSE | 1 | 1 | Press(3)
=============+==============+=============+=============+====================
0 | TRUE | 0 | 0 |
-------------+--------------+-------------+-------------+ Release(button);
0 | TRUE | 0 | 1 |
-------------+--------------+-------------+-------------+--------------------
0 | TRUE | 1 | 0 |
-------------+--------------+-------------+-------------+
0 | TRUE | 1 | 1 |
=============+==============+=============+=============+====================
1 | FALSE | 0 | 0 |
-------------+--------------+-------------+-------------+
1 | FALSE | 0 | 1 |
-------------+--------------+-------------+-------------+
1 | FALSE | 1 | 0 |
-------------+--------------+-------------+-------------+
1 | FALSE | 1 | 1 |
=============+==============+=============+=============+====================
1 | TRUE | 0 | 0 |
-------------+--------------+-------------+-------------+ Release(button);
1 | TRUE | 0 | 1 |
-------------+--------------+-------------+-------------+--------------------
1 | TRUE | 1 | 0 |
-------------+--------------+-------------+-------------+
1 | TRUE | 1 | 1 |
=============+==============+=============+=============+====================
Minimized table:
=============+==============+=============+=============+====================
STATUS bit | button > 0 | btn 1 bit | btn 2 bit | result
=============+==============+=============+=============+====================
0 | FALSE | 1 | 0 | Press(1);
-------------+--------------+-------------+-------------+--------------------
0 | FALSE | 1 | 1 | Press(3);
=============+==============+=============+=============+====================
? | TRUE | 0 | ? | Release(button);
=============+==============+=============+=============+====================
? | TRUE | 1 | ? |
-------------+--------------+-------------+-------------+
1 | FALSE | ? | ? |
-------------+--------------+-------------+-------------+
0 | FALSE | 0 | ? |
=============+==============+=============+=============+====================
The minimized table may be effectively represented
by the following algorithm:
+-------------------+
| STATUS bit change |
+---------+---------+
|
|
V
FALSE +--------------------------------+
X<---------+ button XOR btn 1 bit set |
+---------------+----------------+
| TRUE
|
V
TRUE +---------------+ FALSE
+-------------+ button > 0 +--------------+
| +---------------+ |
| |
V V
+-----------------------+ TRUE +-------------------+
| Release(button); | X<---------+ STATUS bit set |
| button = 0; | +---------+---------+
+---------+-------------+ | FALSE
| |
V V
X +--------------------------------------+
| button = (btn 1 bit) | (btn 2 bit); |
| Press(button); |
+--------------------+-----------------+
|
V
X
Note that the btn bits can be used like this ^^^ because they are in fact
2^0 and 2^1, so the bit OR equals to 1 (btn 1 bit set, btn 2 bit clear)
or 3 (btn 1 bit set, btn 2 bit set).
This was also conveniently used in the implementation.
|
