1 .. include:: <isonum.txt>
2
3 =========================
4 N-Trig touchscreen Driver
5 =========================
6
7 :Copyright: |copy| 2008-2010 Rafi Rubin <rafi@s
8 :Copyright: |copy| 2009-2010 Stephane Chatty
9
10 This driver provides support for N-Trig pen an
11 and multi-touch events are translated to the a
12 the hid and input systems. Pen events are suf
13 are left to the hid core. The driver also pro
14 and utility functions accessible with sysfs an
15
16 This driver has been reported to work properly
17 attached.
18
19
20 Parameters
21 ----------
22
23 Note: values set at load time are global and w
24 devices. Adjusting parameters with sysfs will
25 but only for that one device.
26
27 The following parameters are used to configure
28
29 +-----------------------+---------------------
30 |activate_slack |number of fingers to
31 +-----------------------+---------------------
32 |activation_height, |size threshold to act
33 |activation_width |
34 +-----------------------+---------------------
35 |min_height, |size threshold below
36 |min_width |both to decide activa
37 +-----------------------+---------------------
38 |deactivate_slack |the number of "no con
39 | |propagating the end o
40 +-----------------------+---------------------
41
42 When the last finger is removed from the devic
43 frames. By holding off on deactivation for a
44 erroneous disconnects, where the sensor may mi
45 is still present. Thus deactivate_slack addre
46 see breaks in lines during drawing, or drop an
47
48
49 Additional sysfs items
50 ----------------------
51
52 These nodes just provide easy access to the ra
53
54 +-----------------------+---------------------
55 |sensor_logical_height, | the range for positi
56 |sensor_logical_width |
57 +-----------------------+---------------------
58 |sensor_physical_height,| internal ranges not
59 |sensor_physical_width | useful for tuning
60 +-----------------------+---------------------
61
62 All N-Trig devices with product id of 1 report
63
64 * X: 0-9600
65 * Y: 0-7200
66
67 However not all of these devices have the same
68 seem to be 12" sensors (Dell Latitude XT and X
69 at least one model (Dell Studio 17) has a 17"
70 to logical sizes is used to adjust the size ba
71
72
73 Filtering
74 ---------
75
76 With the release of the early multi-touch firm
77 obvious that these sensors were prone to erron
78 seeing both inappropriately dropped contact an
79 where no finger was actually touching the scre
80
81 Deactivation slack helps prevent dropped conta
82 not address the problem of dropping one of mor
83 are still active. Drops in the multi-touch co
84 processing and should be handled in tandem wit
85
86 As observed ghost contacts are similar to actu
87 seem to have different profiles. Ghost activi
88 short lived touches. As such, I assume that t
89 of events the more likely those events are fro
90 larger the size of each contact the more likel
91 goals of preventing ghosts and accepting real
92 user observable latency), the filter accumulat
93 events until it hits thresholds and begins pro
94 minimizing stored state as well as the cost of
95 I've kept that decision simple.
96
97 Time is measured in terms of the number of fin
98 the probability of multiple simultaneous ghost
99 dramatically with increasing numbers. Rather
100 function of size, I just use it as a binary th
101 contact immediately overrides the waiting peri
102
103 Setting the activation size thresholds to larg
104 primarily on activation slack. If you see lon
105 activation slack while reducing the size thres
106 the ghosts while keeping the screen quite resp
107
108 Contacts continue to be filtered with min_heig
109 the initial activation filter is satisfied. T
110 a mechanism for filtering out ghosts in the fo
111 you actually are using the screen. In practic
112 been far less problematic or relatively rare a
113 set to 0 for both parameters, effectively turn
114
115 I don't know what the optimal values are for t
116 don't work for you, please play with the param
117 values more comfortable, I would appreciate fe
118
119 The calibration of these devices does drift ov
120 dropping worsen and interfere with the normal
121 recalibrating it.
122
123
124 Calibration
125 -----------
126
127 The N-Trig windows tools provide calibration a
128 unofficial unsupported set of user space tools
129 available at:
130 http://code.launchpad.net/~rafi-seas/+junk/ntr
131
132
133 Tracking
134 --------
135
136 As of yet, all tested N-Trig firmwares do not
137 contacts are active they seem to be sorted pri
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