| .. 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/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. |
