[mirror_ubuntu-artful-kernel.git] / Documentation / media / uapi / v4l / dev-teletext.rst

.. -*- 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.
Commit	Line	Data
5377d91f MH	1	.. -- coding: utf-8; mode: rst --
	2
	3	.. _ttx:
	4
	5	******************
	6	Teletext Interface
	7	******************
	8
	9	This interface was aimed at devices receiving and demodulating Teletext
	10	data [:ref:`ets300706`, :ref:`itu653`], evaluating the Teletext
	11	packages and storing formatted pages in cache memory. Such devices are
	12	usually implemented as microcontrollers with serial interface
	13	(I:sup:`2`\ C) and could be found on old TV cards, dedicated Teletext
	14	decoding cards and home-brew devices connected to the PC parallel port.
	15
	16	The Teletext API was designed by Martin Buck. It was defined in the
	17	kernel header file ``linux/videotext.h``, the specification is available
	18	from
	19	`ftp://ftp.gwdg.de/pub/linux/misc/videotext/ <ftp://ftp.gwdg.de/pub/linux/misc/videotext/>`__.
	20	(Videotext is the name of the German public television Teletext
	21	service.)
	22
	23	Eventually the Teletext API was integrated into the V4L API with
	24	character device file names ``/dev/vtx0`` to ``/dev/vtx31``, device
	25	major number 81, minor numbers 192 to 223.
	26
	27	However, teletext decoders were quickly replaced by more generic VBI
	28	demodulators and those dedicated teletext decoders no longer exist. For
	29	many years the vtx devices were still around, even though nobody used
	30	them. So the decision was made to finally remove support for the
	31	Teletext API in kernel 2.6.37.
	32
	33	Modern devices all use the :ref:`raw <raw-vbi>` or
7347081e	34	:ref:`sliced` VBI API.