Teletext for Raspberry Pi
-------------------------

This software generates a teletext signal in software. No hardware
mods are needed.

THIS WILL ONLY WORK ON A PAL TV!

(The demo mode should no longer crash TVs!)

Usage:

Have a Raspberry Pi connected to a TV by composite video in PAL mode.
It doesn't matter if you are running X or not. Dispmanx will draw over
anything else.

Build the programs:

    make

Twiddle the registers:

    sudo ./tvctl on

Ensure you see the message "Teletext output is now on."

Run the demo:

    ./teletext

Press the text button on your TV remote.

Detailed Usage
--------------

    tvctl on|off

This tool prepares the composite out for teletext transmission by
shifting the output picture into the VBI area. It will check the
registers are in a known state before doing anything. "on" and
"off" commands will have no effect if the state is already on or
off, or if the registers are in an unknown state.

    teletext <->

Running with no arguments will show a demo. Running "teletext -"
will read packets from stdin and display them. You can therefore
pipe packets from another tool, possibly over the network with ssh
or netcat.

The packet format is 42 byte raw binary packets, without the clock
run-in. Each packet received will be transmitted once, so you must
send packets endlessly. See

http://www.etsi.org/deliver/etsi_i_ets/300700_300799/300706/01_60/ets_300706e01p.pdf

for details of the teletext protocol.