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| -rw-r--r-- | Documentation/media/uapi/v4l/dev-teletext.rst | 34 |
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diff --git a/Documentation/media/uapi/v4l/dev-teletext.rst b/Documentation/media/uapi/v4l/dev-teletext.rst new file mode 100644 index 000000000..2648f6b37 --- /dev/null +++ b/Documentation/media/uapi/v4l/dev-teletext.rst @@ -0,0 +1,34 @@ +.. -*- 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. |