30 lines
1.5 KiB
XML
30 lines
1.5 KiB
XML
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<title>Teletext Interface</title>
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<para>This interface was aimed at devices receiving and demodulating
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Teletext data [<xref linkend="ets300706" />, <xref linkend="itu653" />], evaluating the
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Teletext packages and storing formatted pages in cache memory. Such
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devices are usually implemented as microcontrollers with serial
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interface (I<superscript>2</superscript>C) and could be found on old
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TV cards, dedicated Teletext decoding cards and home-brew devices
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connected to the PC parallel port.</para>
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<para>The Teletext API was designed by Martin Buck. It was defined in
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the kernel header file <filename>linux/videotext.h</filename>, the
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specification is available from <ulink url="ftp://ftp.gwdg.de/pub/linux/misc/videotext/">
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ftp://ftp.gwdg.de/pub/linux/misc/videotext/</ulink>. (Videotext is the name of
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the German public television Teletext service.)</para>
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<para>Eventually the Teletext API was integrated into the V4L API
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with character device file names <filename>/dev/vtx0</filename> to
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<filename>/dev/vtx31</filename>, device major number 81, minor numbers
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192 to 223.</para>
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<para>However, teletext decoders were quickly replaced by more
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generic VBI demodulators and those dedicated teletext decoders no longer exist.
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For 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 Teletext API in
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kernel 2.6.37.</para>
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<para>Modern devices all use the <link linkend="raw-vbi">raw</link> or
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<link linkend="sliced">sliced</link> VBI API.</para>
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