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diff --git a/Documentation/input/ntrig.txt b/Documentation/input/ntrig.txt deleted file mode 100644 index be1fd981f73f..000000000000 --- a/Documentation/input/ntrig.txt +++ /dev/null @@ -1,126 +0,0 @@ -N-Trig touchscreen Driver -------------------------- - Copyright (c) 2008-2010 Rafi Rubin <rafi@seas.upenn.edu> - Copyright (c) 2009-2010 Stephane Chatty - -This driver provides support for N-Trig pen and multi-touch sensors. Single -and multi-touch events are translated to the appropriate protocols for -the hid and input systems. Pen events are sufficiently hid compliant and -are left to the hid core. The driver also provides additional filtering -and utility functions accessible with sysfs and module parameters. - -This driver has been reported to work properly with multiple N-Trig devices -attached. - - -Parameters ----------- - -Note: values set at load time are global and will apply to all applicable -devices. Adjusting parameters with sysfs will override the load time values, -but only for that one device. - -The following parameters are used to configure filters to reduce noise: - -activate_slack number of fingers to ignore before processing events - -activation_height size threshold to activate immediately -activation_width - -min_height size threshold bellow which fingers are ignored -min_width both to decide activation and during activity - -deactivate_slack the number of "no contact" frames to ignore before - propagating the end of activity events - -When the last finger is removed from the device, it sends a number of empty -frames. By holding off on deactivation for a few frames we can tolerate false -erroneous disconnects, where the sensor may mistakenly not detect a finger that -is still present. Thus deactivate_slack addresses problems where a users might -see breaks in lines during drawing, or drop an object during a long drag. - - -Additional sysfs items ----------------------- - -These nodes just provide easy access to the ranges reported by the device. -sensor_logical_height the range for positions reported during activity -sensor_logical_width - -sensor_physical_height internal ranges not used for normal events but -sensor_physical_width useful for tuning - -All N-Trig devices with product id of 1 report events in the ranges of -X: 0-9600 -Y: 0-7200 -However not all of these devices have the same physical dimensions. Most -seem to be 12" sensors (Dell Latitude XT and XT2 and the HP TX2), and -at least one model (Dell Studio 17) has a 17" sensor. The ratio of physical -to logical sizes is used to adjust the size based filter parameters. - - -Filtering ---------- - -With the release of the early multi-touch firmwares it became increasingly -obvious that these sensors were prone to erroneous events. Users reported -seeing both inappropriately dropped contact and ghosts, contacts reported -where no finger was actually touching the screen. - -Deactivation slack helps prevent dropped contact for single touch use, but does -not address the problem of dropping one of more contacts while other contacts -are still active. Drops in the multi-touch context require additional -processing and should be handled in tandem with tacking. - -As observed ghost contacts are similar to actual use of the sensor, but they -seem to have different profiles. Ghost activity typically shows up as small -short lived touches. As such, I assume that the longer the continuous stream -of events the more likely those events are from a real contact, and that the -larger the size of each contact the more likely it is real. Balancing the -goals of preventing ghosts and accepting real events quickly (to minimize -user observable latency), the filter accumulates confidence for incoming -events until it hits thresholds and begins propagating. In the interest in -minimizing stored state as well as the cost of operations to make a decision, -I've kept that decision simple. - -Time is measured in terms of the number of fingers reported, not frames since -the probability of multiple simultaneous ghosts is expected to drop off -dramatically with increasing numbers. Rather than accumulate weight as a -function of size, I just use it as a binary threshold. A sufficiently large -contact immediately overrides the waiting period and leads to activation. - -Setting the activation size thresholds to large values will result in deciding -primarily on activation slack. If you see longer lived ghosts, turning up the -activation slack while reducing the size thresholds may suffice to eliminate -the ghosts while keeping the screen quite responsive to firm taps. - -Contacts continue to be filtered with min_height and min_width even after -the initial activation filter is satisfied. The intent is to provide -a mechanism for filtering out ghosts in the form of an extra finger while -you actually are using the screen. In practice this sort of ghost has -been far less problematic or relatively rare and I've left the defaults -set to 0 for both parameters, effectively turning off that filter. - -I don't know what the optimal values are for these filters. If the defaults -don't work for you, please play with the parameters. If you do find other -values more comfortable, I would appreciate feedback. - -The calibration of these devices does drift over time. If ghosts or contact -dropping worsen and interfere with the normal usage of your device, try -recalibrating it. - - -Calibration ------------ - -The N-Trig windows tools provide calibration and testing routines. Also an -unofficial unsupported set of user space tools including a calibrator is -available at: -http://code.launchpad.net/~rafi-seas/+junk/ntrig_calib - - -Tracking --------- - -As of yet, all tested N-Trig firmwares do not track fingers. When multiple -contacts are active they seem to be sorted primarily by Y position. |