flightgear/src/Main/morse.hxx

// morse.hxx -- Morse code generation class
//
// Written by Curtis Olson, started March 2001.
//
// Copyright (C) 2001  Curtis L. Olson - curt@flightgear.org
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
//
// $Id$


#ifndef _MORSE_HXX
#define _MORSE_HXX

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include <simgear/compiler.h>

#include <plib/sl.h>
#include <plib/sm.h>


// Quoting from http://www.kluft.com/~ikluft/ham/morse-intro.html by
// Ian Kluft KO6YQ <ikluft@kluft.com>
//
// [begin quote]
//
// What is the Standard for Measuring Morse Code Speed?
// 
// [This was adapted from the Ham Radio FAQ which used to be posted on UseNet.] 
// 
// The word PARIS was chosen as the standard length for CW code
// speed. Each dit counts for one count, each dah counts for three
// counts, intra-character spacing is one count, inter-character
// spacing is three counts and inter-word spacing is seven counts, so
// the word PARIS is exactly 50 counts:
// 
// PPPPPPPPPPPPPP    AAAAAA    RRRRRRRRRR    IIIIII    SSSSSSSSSS
// di  da  da  di    di  da    di  da  di    di  di    di  di  di
// 1 1 3 1 3 1 1  3  1 1 3  3  1 1 3 1 1  3  1 1 1  3  1 1 1 1 1  7 = 50
//   ^                      ^                                     ^
//   ^Intra-character       ^Inter-character            Inter-word^
// 
// So 5 words-per-minute = 250 counts-per-minute / 50 counts-per-word
// or one count every 240 milliseconds. 13 words-per-minute is one
// count every ~92.3 milliseconds. This method of sending code is
// sometimes called "Slow Code", because at 5 wpm it sounds VERY SLOW.
// 
// The "Farnsworth" method is accomplished by sending the dits and
// dahs and intra-character spacing at a higher speed, then increasing
// the inter-character and inter-word spacing to slow the sending
// speed down to the desired speed. For example, to send at 5 wpm with
// 13 wpm characters in Farnsworth method, the dits and
// intra-character spacing would be 92.3 milliseconds, the dah would
// be 276.9 milliseconds, the inter-character spacing would be 1.443
// seconds and inter-word spacing would be 3.367 seconds.
//
// [end quote]

// Ok, back to Curt 

// My formulation is based dit = 1 count, dah = 3 counts, 1 count for
// intRA-character space, 3 counts for intER-character space.  Target
// is 5 wpm which by the above means 1 count = 240 milliseconds.
// 
// AIM 1-1-7 (f) states that the frequency of the tone should be 1020
// Hz for the VOR ident.


static const char DI = '1';
static const char DIT = '1';
static const char DA = '2';
static const char DAH = '2';
static const char end = '0';

static const int BYTES_PER_SECOND = 8000;
static const int BEAT_LENGTH = 240; // milleseconds (5 wpm)
static const int TRANSITION_BYTES = 40;
static const int COUNT_SIZE = BYTES_PER_SECOND * BEAT_LENGTH / 1000;
static const int DIT_SIZE = 2 * COUNT_SIZE;   // 2 counts
static const int DAH_SIZE = 4 * COUNT_SIZE;   // 4 counts
static const int SPACE_SIZE = 3 * COUNT_SIZE; // 3 counts
static const int FREQUENCY = 1020;	 // AIM 1-1-7 (f) specified in Hz

static char alphabet[26][4] = {
    { DI, DAH, end, end },	/* A */ 
    { DA, DI, DI, DIT },	/* B */ 
    { DA, DI, DA, DIT },	/* C */ 
    { DA, DI, DIT, end },	/* D */ 
    { DIT, end, end, end },	/* E */ 
    { DI, DI, DA, DIT },	/* F */ 
    { DA, DA, DIT, end },	/* G */ 
    { DI, DI, DI, DIT },	/* H */ 
    { DI, DIT, end, end },	/* I */ 
    { DI, DA, DA, DAH },	/* J */ 
    { DA, DI, DAH, end },	/* K */ 
    { DI, DA, DI, DIT },	/* L */ 
    { DA, DAH, end, end },	/* M */ 
    { DA, DIT, end, end },	/* N */ 
    { DA, DA, DAH, end },	/* O */ 
    { DI, DA, DA, DIT },	/* P */ 
    { DA, DA, DI, DAH },	/* Q */ 
    { DI, DA, DIT, end },	/* R */ 
    { DI, DI, DIT, end },	/* S */ 
    { DAH, end, end, end },	/* T */ 
    { DI, DI, DAH, end },	/* U */ 
    { DI, DI, DI, DAH },	/* V */ 
    { DI, DA, DAH, end },	/* W */ 
    { DA, DI, DI, DAH },	/* X */ 
    { DA, DI, DA, DAH },	/* Y */ 
    { DA, DA, DI, DIT }		/* Z */ 
};

// manages everything we need to know for an individual sound sample
class FGMorse {

    unsigned char dit[ DIT_SIZE ] ;
    unsigned char dah[ DAH_SIZE ] ;
    unsigned char space[ SPACE_SIZE ] ;

public:

    FGMorse();
    ~FGMorse();

    // allocate and initialize sound samples
    bool init();
};


#endif // _MORSE_HXX