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1 <title>Teletext Interface</title> 1 <title>Teletext Interface</title>
2 2
3 <para>This interface aims at devices receiving and demodulating 3 <para>This interface was aimed at devices receiving and demodulating
4Teletext data [<xref linkend="ets300706" />, <xref linkend="itu653" />], evaluating the 4Teletext data [<xref linkend="ets300706" />, <xref linkend="itu653" />], evaluating the
5Teletext packages and storing formatted pages in cache memory. Such 5Teletext packages and storing formatted pages in cache memory. Such
6devices are usually implemented as microcontrollers with serial 6devices are usually implemented as microcontrollers with serial
7interface (I<superscript>2</superscript>C) and can be found on older 7interface (I<superscript>2</superscript>C) and could be found on old
8TV cards, dedicated Teletext decoding cards and home-brew devices 8TV cards, dedicated Teletext decoding cards and home-brew devices
9connected to the PC parallel port.</para> 9connected to the PC parallel port.</para>
10 10
11 <para>The Teletext API was designed by Martin Buck. It is defined in 11 <para>The Teletext API was designed by Martin Buck. It was defined in
12the kernel header file <filename>linux/videotext.h</filename>, the 12the kernel header file <filename>linux/videotext.h</filename>, the
13specification is available from <ulink url="ftp://ftp.gwdg.de/pub/linux/misc/videotext/"> 13specification is available from <ulink url="ftp://ftp.gwdg.de/pub/linux/misc/videotext/">
14ftp://ftp.gwdg.de/pub/linux/misc/videotext/</ulink>. (Videotext is the name of 14ftp://ftp.gwdg.de/pub/linux/misc/videotext/</ulink>. (Videotext is the name of
15the German public television Teletext service.) Conventional character 15the German public television Teletext service.)</para>
16device file names are <filename>/dev/vtx</filename> and
17<filename>/dev/vttuner</filename>, with device number 83, 0 and 83, 16
18respectively. A similar interface exists for the Philips SAA5249
19Teletext decoder [specification?] with character device file names
20<filename>/dev/tlkN</filename>, device number 102, N.</para>
21 16
22 <para>Eventually the Teletext API was integrated into the V4L API 17 <para>Eventually the Teletext API was integrated into the V4L API
23with character device file names <filename>/dev/vtx0</filename> to 18with character device file names <filename>/dev/vtx0</filename> to
24<filename>/dev/vtx31</filename>, device major number 81, minor numbers 19<filename>/dev/vtx31</filename>, device major number 81, minor numbers
25192 to 223. For reference the V4L Teletext API specification is 20192 to 223.</para>
26reproduced here in full: "Teletext interfaces talk the existing VTX
27API." Teletext devices with major number 83 and 102 will be removed in
28Linux 2.6.</para>
29 21
30 <para>There are no plans to replace the Teletext API or to integrate 22 <para>However, teletext decoders were quickly replaced by more
31it into V4L2. Please write to the linux-media mailing list: &v4l-ml; 23generic VBI demodulators and those dedicated teletext decoders no longer exist.
32when the need arises.</para> 24For many years the vtx devices were still around, even though nobody used
25them. So the decision was made to finally remove support for the Teletext API in
26kernel 2.6.37.</para>
27
28 <para>Modern devices all use the <link linkend="raw-vbi">raw</link> or
29<link linkend="sliced">sliced</link> VBI API.</para>
33 30
34 <!-- 31 <!--
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