Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 34 insertions, 0 deletions

diff --git a/Documentation/media/uapi/v4l/dev-teletext.rst b/Documentation/media/uapi/v4l/dev-teletext.rst
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+.. -*- coding: utf-8; mode: rst -*-
+
+.. _ttx:
+
+******************
+Teletext Interface
+******************
+
+This interface was aimed at devices receiving and demodulating Teletext
+data [:ref:`ets300706`, :ref:`itu653`], evaluating the Teletext
+packages and storing formatted pages in cache memory. Such devices are
+usually implemented as microcontrollers with serial interface
+(I:sup:`2`\ C) and could be found on old TV cards, dedicated Teletext
+decoding cards and home-brew devices connected to the PC parallel port.
+
+The Teletext API was designed by Martin Buck. It was defined in the
+kernel header file ``linux/videotext.h``, the specification is available
+from
+`ftp://ftp.gwdg.de/pub/linux/misc/videotext/ <ftp://ftp.gwdg.de/pub/linux/misc/videotext/>`__.
+(Videotext is the name of the German public television Teletext
+service.)
+
+Eventually the Teletext API was integrated into the V4L API with
+character device file names ``/dev/vtx0`` to ``/dev/vtx31``, device
+major number 81, minor numbers 192 to 223.
+
+However, teletext decoders were quickly replaced by more generic VBI
+demodulators and those dedicated teletext decoders no longer exist. For
+many years the vtx devices were still around, even though nobody used
+them. So the decision was made to finally remove support for the
+Teletext API in kernel 2.6.37.
+
+Modern devices all use the :ref:`raw <raw-vbi>` or
+:ref:`sliced` VBI API.