Markus Heiser | 5377d91 | 2016-06-30 15:18:56 +0200 | [diff] [blame] | 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 |
Mauro Carvalho Chehab | 7347081 | 2016-07-01 13:58:44 -0300 | [diff] [blame] | 34 | :ref:`sliced` VBI API. |