mirror of https://gitee.com/openkylin/linux.git
35 lines
1.4 KiB
ReStructuredText
35 lines
1.4 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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.. _ttx:
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******************
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Teletext Interface
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******************
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This interface was aimed at devices receiving and demodulating Teletext
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data [:ref:`ets300706`, :ref:`itu653`], evaluating the Teletext
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packages and storing formatted pages in cache memory. Such devices are
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usually implemented as microcontrollers with serial interface
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(I:sup:`2`\ C) and could be found on old TV cards, dedicated Teletext
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decoding cards and home-brew devices connected to the PC parallel port.
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The Teletext API was designed by Martin Buck. It was defined in the
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kernel header file ``linux/videotext.h``, the specification is available
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from
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`ftp://ftp.gwdg.de/pub/linux/misc/videotext/ <ftp://ftp.gwdg.de/pub/linux/misc/videotext/>`__.
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(Videotext is the name of the German public television Teletext
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service.)
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Eventually the Teletext API was integrated into the V4L API with
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character device file names ``/dev/vtx0`` to ``/dev/vtx31``, device
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major number 81, minor numbers 192 to 223.
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However, teletext decoders were quickly replaced by more generic VBI
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demodulators and those dedicated teletext decoders no longer exist. For
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many years the vtx devices were still around, even though nobody used
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them. So the decision was made to finally remove support for the
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Teletext API in kernel 2.6.37.
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Modern devices all use the :ref:`raw <raw-vbi>` or
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:ref:`sliced` VBI API.
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