40 lines
1.9 KiB
XML
40 lines
1.9 KiB
XML
<title>Teletext Interface</title>
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<para>This interface aims 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 can be found on older
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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 is 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.) Conventional character
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device file names are <filename>/dev/vtx</filename> and
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<filename>/dev/vttuner</filename>, with device number 83, 0 and 83, 16
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respectively. A similar interface exists for the Philips SAA5249
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Teletext decoder [specification?] with character device file names
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<filename>/dev/tlkN</filename>, device number 102, N.</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. For reference the V4L Teletext API specification is
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reproduced here in full: "Teletext interfaces talk the existing VTX
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API." Teletext devices with major number 83 and 102 will be removed in
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Linux 2.6.</para>
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<para>There are no plans to replace the Teletext API or to integrate
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it into V4L2. Please write to the linux-media mailing list: &v4l-ml;
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when the need arises.</para>
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