| Mauro Carvalho Chehab | 8e080c2 | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 1 | <title>Teletext Interface</title> |
| 2 | |
| Hans Verkuil | f44026d | 2010-08-06 12:52:43 -0300 | [diff] [blame] | 3 | <para>This interface was aimed at devices receiving and demodulating |
| Mauro Carvalho Chehab | 8e080c2 | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 4 | Teletext data [<xref linkend="ets300706" />, <xref linkend="itu653" />], evaluating the |
| 5 | Teletext packages and storing formatted pages in cache memory. Such |
| 6 | devices are usually implemented as microcontrollers with serial |
| Hans Verkuil | f44026d | 2010-08-06 12:52:43 -0300 | [diff] [blame] | 7 | interface (I<superscript>2</superscript>C) and could be found on old |
| Mauro Carvalho Chehab | 8e080c2 | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 8 | TV cards, dedicated Teletext decoding cards and home-brew devices |
| 9 | connected to the PC parallel port.</para> |
| 10 | |
| Hans Verkuil | f44026d | 2010-08-06 12:52:43 -0300 | [diff] [blame] | 11 | <para>The Teletext API was designed by Martin Buck. It was defined in |
| Mauro Carvalho Chehab | 8e080c2 | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 12 | the kernel header file <filename>linux/videotext.h</filename>, the |
| Mauro Carvalho Chehab | e5b2021 | 2009-09-15 20:49:43 -0300 | [diff] [blame] | 13 | specification is available from <ulink url="ftp://ftp.gwdg.de/pub/linux/misc/videotext/"> |
| 14 | ftp://ftp.gwdg.de/pub/linux/misc/videotext/</ulink>. (Videotext is the name of |
| Hans Verkuil | f44026d | 2010-08-06 12:52:43 -0300 | [diff] [blame] | 15 | the German public television Teletext service.)</para> |
| Mauro Carvalho Chehab | 8e080c2 | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 16 | |
| 17 | <para>Eventually the Teletext API was integrated into the V4L API |
| 18 | with character device file names <filename>/dev/vtx0</filename> to |
| 19 | <filename>/dev/vtx31</filename>, device major number 81, minor numbers |
| Hans Verkuil | f44026d | 2010-08-06 12:52:43 -0300 | [diff] [blame] | 20 | 192 to 223.</para> |
| Mauro Carvalho Chehab | 8e080c2 | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 21 | |
| Hans Verkuil | f44026d | 2010-08-06 12:52:43 -0300 | [diff] [blame] | 22 | <para>However, teletext decoders were quickly replaced by more |
| 23 | generic VBI demodulators and those dedicated teletext decoders no longer exist. |
| 24 | For many years the vtx devices were still around, even though nobody used |
| 25 | them. So the decision was made to finally remove support for the Teletext API in |
| 26 | kernel 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> |