media: dev-teletext.rst: remove obsolete teletext interface

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.. 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/media/uapi/fdl-appendix.rst.

..

.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections

.. _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.

    dev-codec

    dev-raw-vbi

    dev-sliced-vbi

    dev-teletext

    dev-radio

    dev-rds

    dev-sdr