| .. -*- 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. |