mirror of https://gitee.com/openkylin/linux.git
30 lines
1.5 KiB
XML
30 lines
1.5 KiB
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>
|