V4L/DVB: Documentation: update now that the vtx/videotext API has been removed

[deliverable/linux.git] / Documentation / DocBook / v4l / dev-teletext.xml

  <title>Teletext Interface</title>

  <para>This interface was aimed at devices receiving and demodulating
Teletext data [<xref linkend="ets300706" />, <xref linkend="itu653" />], evaluating the
Teletext packages and storing formatted pages in cache memory. Such
devices are usually implemented as microcontrollers with serial
interface (I<superscript>2</superscript>C) and could be found on old
TV cards, dedicated Teletext decoding cards and home-brew devices
connected to the PC parallel port.</para>

  <para>The Teletext API was designed by Martin Buck. It was defined in
the kernel header file <filename>linux/videotext.h</filename>, the
specification is available from <ulink url="ftp://ftp.gwdg.de/pub/linux/misc/videotext/">
ftp://ftp.gwdg.de/pub/linux/misc/videotext/</ulink>. (Videotext is the name of
the German public television Teletext service.)</para>

  <para>Eventually the Teletext API was integrated into the V4L API
with character device file names <filename>/dev/vtx0</filename> to
<filename>/dev/vtx31</filename>, device major number 81, minor numbers
192 to 223.</para>

  <para>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.</para>

  <para>Modern devices all use the <link linkend="raw-vbi">raw</link> or
<link linkend="sliced">sliced</link> VBI API.</para>

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