| <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> |