Mauro Carvalho Chehab | 8e080c2 | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 1 | <title>Teletext Interface</title> |
| 2 | |
| 3 | <para>This interface aims at devices receiving and demodulating |
| 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 |
| 7 | interface (I<superscript>2</superscript>C) and can be found on older |
| 8 | TV cards, dedicated Teletext decoding cards and home-brew devices |
| 9 | connected to the PC parallel port.</para> |
| 10 | |
| 11 | <para>The Teletext API was designed by Martin Buck. It is defined in |
| 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 |
Mauro Carvalho Chehab | 8e080c2 | 2009-09-13 22:16:04 -0300 | [diff] [blame] | 15 | the German public television Teletext service.) Conventional character |
| 16 | device file names are <filename>/dev/vtx</filename> and |
| 17 | <filename>/dev/vttuner</filename>, with device number 83, 0 and 83, 16 |
| 18 | respectively. A similar interface exists for the Philips SAA5249 |
| 19 | Teletext decoder [specification?] with character device file names |
| 20 | <filename>/dev/tlkN</filename>, device number 102, N.</para> |
| 21 | |
| 22 | <para>Eventually the Teletext API was integrated into the V4L API |
| 23 | with character device file names <filename>/dev/vtx0</filename> to |
| 24 | <filename>/dev/vtx31</filename>, device major number 81, minor numbers |
| 25 | 192 to 223. For reference the V4L Teletext API specification is |
| 26 | reproduced here in full: "Teletext interfaces talk the existing VTX |
| 27 | API." Teletext devices with major number 83 and 102 will be removed in |
| 28 | Linux 2.6.</para> |
| 29 | |
| 30 | <para>There are no plans to replace the Teletext API or to integrate |
| 31 | it into V4L2. Please write to the linux-media mailing list: &v4l-ml; |
| 32 | when the need arises.</para> |
| 33 | |
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