Documentation/input/devices/ntrig.rst

Source file repositories/reference/linux-study-clean/Documentation/input/devices/ntrig.rst

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Documentation/input/devices/ntrig.rst
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Support Tooling And Documentation: documentation
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.. include:: <isonum.txt>

=========================
N-Trig touchscreen Driver
=========================

:Copyright: |copy| 2008-2010 Rafi Rubin <rafi@seas.upenn.edu>
:Copyright: |copy| 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 below 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.

Annotation

Implementation Notes