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diff --git a/Documentation/media/uapi/v4l/dev-touch.rst b/Documentation/media/uapi/v4l/dev-touch.rst new file mode 100644 index 0000000..1f4e752 --- /dev/null +++ b/Documentation/media/uapi/v4l/dev-touch.rst @@ -0,0 +1,56 @@ +.. -*- coding: utf-8; mode: rst -*- + +.. _touch: + +************* +Touch Devices +************* + +Touch devices are accessed through character device special files named +``/dev/v4l-touch0`` to ``/dev/v4l-touch255`` with major number 81 and +dynamically allocated minor numbers 0 to 255. + +Overview +======== + +Sensors may be Optical, or Projected Capacitive touch (PCT). + +Processing is required to analyse the raw data and produce input events. In +some systems, this may be performed on the ASIC and the raw data is purely a +side-channel for diagnostics or tuning. In other systems, the ASIC is a simple +analogue front end device which delivers touch data at high rate, and any touch +processing must be done on the host. + +For capacitive touch sensing, the touchscreen is composed of an array of +horizontal and vertical conductors (alternatively called rows/columns, X/Y +lines, or tx/rx). Mutual Capacitance measured is at the nodes where the +conductors cross. Alternatively, Self Capacitance measures the signal from each +column and row independently. + +A touch input may be determined by comparing the raw capacitance measurement to +a no-touch reference (or "baseline") measurement: + +Delta = Raw - Reference + +The reference measurement takes account of variations in the capacitance across +the touch sensor matrix, for example manufacturing irregularities, +environmental or edge effects. + +Querying Capabilities +===================== + +Devices supporting the touch interface set the ``V4L2_CAP_VIDEO_CAPTURE`` flag +and the ``V4L2_CAP_TOUCH`` flag in the ``capabilities`` field of +:ref:`v4l2_capability <v4l2-capability>` returned by the +:ref:`VIDIOC_QUERYCAP` ioctl. + +At least one of the read/write or streaming I/O methods must be +supported. + +The formats supported by touch devices are documented in +:ref:`Touch Formats <tch-formats>`. + +Data Format Negotiation +======================= + +A touch device may support any I/O method. |