From 54f38fcae536ea202ce7d6a359521492fba30c1f Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Wed, 4 Mar 2020 10:21:39 +0100 Subject: media: docs: move uAPI book to userspace-api/media Since 2017, there is an space reserved for userspace API, created by changeset 1d596dee3862 ("docs: Create a user-space API guide"). As the media subsystem was one of the first subsystems to use Sphinx, until this patch, we were keeping things on a separate place. Let's just use the new location, as having all uAPI altogether will likely make things easier for developers. Signed-off-by: Mauro Carvalho Chehab --- .../userspace-api/media/v4l/dev-touch.rst | 63 ++++++++++++++++++++++ 1 file changed, 63 insertions(+) create mode 100644 Documentation/userspace-api/media/v4l/dev-touch.rst (limited to 'Documentation/userspace-api/media/v4l/dev-touch.rst') diff --git a/Documentation/userspace-api/media/v4l/dev-touch.rst b/Documentation/userspace-api/media/v4l/dev-touch.rst new file mode 100644 index 000000000000..c1ce446274f2 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/dev-touch.rst @@ -0,0 +1,63 @@ +.. Permission is granted to copy, distribute and/or modify this +.. document under the terms of the GNU Free Documentation License, +.. Version 1.1 or any later version published by the Free Software +.. Foundation, with no Invariant Sections, no Front-Cover Texts +.. and no Back-Cover Texts. A copy of the license is included at +.. Documentation/userspace-api/media/fdl-appendix.rst. +.. +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections + +.. _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 +:c:type:`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 `. + +Data Format Negotiation +======================= + +A touch device may support any I/O method. -- cgit v1.2.3