gen_tone.c

//
//    This file is part of Dire Wolf, an amateur radio packet TNC.
//
//    Copyright (C) 2011, 2014, 2015  John Langner, WB2OSZ
//
//    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, see <http://www.gnu.org/licenses/>.
//


/*------------------------------------------------------------------
 *
 * Module:      gen_tone.c
 *
 * Purpose:     Convert bits to AFSK for writing to .WAV sound file 
 *		or a sound device.
 *
 *
 *---------------------------------------------------------------*/

#include <stdio.h>
#include <math.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>

#include "direwolf.h"
#include "audio.h"
#include "gen_tone.h"
#include "textcolor.h"

#include "fsk_demod_state.h"	/* for MAX_FILTER_SIZE which might be overly generous for here. */
				/* but safe if we use same size as for receive. */
#include "dsp.h"


// Properties of the digitized sound stream & modem.

static struct audio_s *save_audio_config_p;

/*
 * 8 bit samples are unsigned bytes in range of 0 .. 255.
 *
 * 16 bit samples are signed short in range of -32768 .. +32767.
 */


/* Constants after initialization. */

#define TICKS_PER_CYCLE ( 256.0 * 256.0 * 256.0 * 256.0 )

static int ticks_per_sample[MAX_CHANS];	/* Same for both channels of same soundcard */
					/* because they have same sample rate */
					/* but less confusing to have for each channel. */

static int ticks_per_bit[MAX_CHANS];
static int f1_change_per_sample[MAX_CHANS];
static int f2_change_per_sample[MAX_CHANS];

static short sine_table[256];


/* Accumulators. */

static unsigned int tone_phase[MAX_CHANS]; // Phase accumulator for tone generation.
					    // Upper bits are used as index into sine table.

static int bit_len_acc[MAX_CHANS];	// To accumulate fractional samples per bit.

static int lfsr[MAX_CHANS];		// Shift register for scrambler.


/*
 * The K9NG/G3RUH output originally took a very simple and lazy approach.
 * We simply generated a square wave with + or - the desired amplitude.
 * This has a couple undesirable properties.
 *
 *	- Transmitting a square wave would splatter into adjacent
 *	   channels of the transmitter doesn't limit the bandwidth.
 *
 *	- The usual sample rate of 44100 is not a multiple of the 
 *	   baud rate so jitter would be added to the zero crossings.
 *
 * Starting in version 1.2, we try to overcome these issues by using
 * a higher sample rate, low pass filtering, and down sampling.
 *
 * What sort of low pass filter would be appropriate?  Intuitively,
 * we would expect a cutoff frequency somewhere between baud/2 and baud.
 * The current values were found with a small amount of trial and 
 * error for best results.  Future improvement is certainly possible.
 */

/* 
 * For low pass filtering of 9600 baud data. 
 */

/* Add sample to buffer and shift the rest down. */
// TODO:  Can we have one copy of these in dsp.h?

static inline void push_sample (float val, float *buff, int size)
{
	memmove(buff+1,buff,(size-1)*sizeof(float));
	buff[0] = val; 
}


/* FIR filter kernel. */

static inline float convolve (const float *data, const float *filter, int filter_size)
{
	  float sum = 0;
	  int j;

	  for (j=0; j<filter_size; j++) {
	    sum += filter[j] * data[j];
	  }
	  return (sum);
}

static int lp_filter_size[MAX_CHANS];
static float raw[MAX_CHANS][MAX_FILTER_SIZE] __attribute__((aligned(16)));
static float lp_filter[MAX_CHANS][MAX_FILTER_SIZE] __attribute__((aligned(16)));
static int resample[MAX_CHANS];

#define UPSAMPLE 2


/*------------------------------------------------------------------
 *
 * Name:        gen_tone_init
 *
 * Purpose:     Initialize for AFSK tone generation which might
 *		be used for RTTY or amateur packet radio.
 *
 * Inputs:      audio_config_p		- Pointer to modem parameter structure, modem_s.
 *
 *				The fields we care about are:
 *
 *					samples_per_sec
 *					baud
 *					mark_freq
 *					space_freq
 *					samples_per_sec
 *
 *		amp		- Signal amplitude on scale of 0 .. 100.
 *
 * Returns:     0 for success.
 *              -1 for failure.
 *
 * Description:	 Calculate various constants for use by the direct digital synthesis
 * 		audio tone generation.
 *
 *----------------------------------------------------------------*/

static int amp16bit;	/* for 9600 baud */


int gen_tone_init (struct audio_s *audio_config_p, int amp)  
{
	int j;
	int chan = 0;
	
/* 
 * Save away modem parameters for later use. 
 */

	save_audio_config_p = audio_config_p;
	

	amp16bit = (32767 * amp) / 100;


	for (chan = 0; chan < MAX_CHANS; chan++) {

	  if (audio_config_p->achan[chan].valid) {

	    int a = ACHAN2ADEV(chan);

	    ticks_per_sample[chan] = (int) ((TICKS_PER_CYCLE / (double)audio_config_p->adev[a].samples_per_sec ) + 0.5);

	    ticks_per_bit[chan] = (int) ((TICKS_PER_CYCLE / (double)audio_config_p->achan[chan].baud ) + 0.5);

	    f1_change_per_sample[chan] = (int) (((double)audio_config_p->achan[chan].mark_freq * TICKS_PER_CYCLE / (double)audio_config_p->adev[a].samples_per_sec ) + 0.5);

	    f2_change_per_sample[chan] = (int) (((double)audio_config_p->achan[chan].space_freq * TICKS_PER_CYCLE / (double)audio_config_p->adev[a].samples_per_sec ) + 0.5);

	    tone_phase[chan] = 0;
				
	    bit_len_acc[chan] = 0;

	    lfsr[chan] = 0;
	  }
	}

        for (j=0; j<256; j++) {
	  double a;
	  int s;

	  a = ((double)(j) / 256.0) * (2 * M_PI);
	  s = (int) (sin(a) * 32767 * amp / 100.0);

	  /* 16 bit sound sample is in range of -32768 .. +32767. */
	  
	  assert (s >= -32768 && s <= 32767);
	
	  sine_table[j] = s;
        }


/*
 * Low pass filter for 9600 baud. 
 */

	for (chan = 0; chan < MAX_CHANS; chan++) {

	  if (audio_config_p->achan[chan].valid && 
		(audio_config_p->achan[chan].modem_type == MODEM_SCRAMBLE 
		  ||  audio_config_p->achan[chan].modem_type == MODEM_BASEBAND)) {

	    int a = ACHAN2ADEV(chan);
	    int samples_per_sec;		/* Might be scaled up! */
	    int baud;

	    /* These numbers were by trial and error.  Need more investigation here. */

	    float filter_len_bits =  88 * 9600.0 / (44100.0 * 2.0);
						/* Filter length in number of data bits. */	
	
	    float lpf_baud = 0.8;		/* Lowpass cutoff freq as fraction of baud rate */

	    float fc;				/* Cutoff frequency as fraction of sampling frequency. */


	    samples_per_sec = audio_config_p->adev[a].samples_per_sec * UPSAMPLE;		
	    baud = audio_config_p->achan[chan].baud;

	    ticks_per_sample[chan] = (int) ((TICKS_PER_CYCLE / (double)samples_per_sec ) + 0.5);
	    ticks_per_bit[chan] = (int) ((TICKS_PER_CYCLE / (double)baud ) + 0.5);

	    lp_filter_size[chan] = (int) (( filter_len_bits * (float)samples_per_sec / baud) + 0.5);

	    if (lp_filter_size[chan] < 10 || lp_filter_size[chan] > MAX_FILTER_SIZE) {
	      text_color_set(DW_COLOR_ERROR);
	      dw_printf ("gen_tone_init: INTERNAL ERROR, chan %d, lp_filter_size %d\n", chan, lp_filter_size[chan]);
	      lp_filter_size[chan] = MAX_FILTER_SIZE / 2;
	    }

	    fc = (float)baud * lpf_baud / (float)samples_per_sec;

	    //text_color_set(DW_COLOR_DEBUG);
	    //dw_printf ("gen_tone_init: chan %d, call gen_lowpass(fc=%.2f, , size=%d, )\n", chan, fc, lp_filter_size[chan]);

	    gen_lowpass (fc, lp_filter[chan], lp_filter_size[chan], BP_WINDOW_HAMMING);

	  }
	}

	return (0);

 } /* end gen_tone_init */


/*-------------------------------------------------------------------
 *
 * Name:        gen_tone_put_bit
 *
 * Purpose:     Generate tone of proper duration for one data bit.
 *
 * Inputs:      chan	- Audio channel, 0 = first.
 *
 *		dat	- 0 for f1, 1 for f2.
 *
 * 			  	-1 inserts half bit to test data	
 *				recovery PLL.
 *
 * Assumption:  fp is open to a file for write.
 *
 *--------------------------------------------------------------------*/

static void put_sample (int chan, int a, int sam);

void tone_gen_put_bit (int chan, int dat)
{
	int a = ACHAN2ADEV(chan);	/* device for channel. */


	assert (save_audio_config_p->achan[chan].valid);


        if (dat < 0) { 
	  /* Hack to test receive PLL recovery. */
	  bit_len_acc[chan] -= ticks_per_bit[chan]; 
	  dat = 0; 
	} 

	if (save_audio_config_p->achan[chan].modem_type == MODEM_SCRAMBLE) {
	  int x;

	  x = (dat ^ (lfsr[chan] >> 16) ^ (lfsr[chan] >> 11)) & 1;
	  lfsr[chan] = (lfsr[chan] << 1) | (x & 1);
	  dat = x;
	}
	  
	do {

	  if (save_audio_config_p->achan[chan].modem_type == MODEM_AFSK) {
	    int sam;

	    tone_phase[chan] += dat ? f2_change_per_sample[chan] : f1_change_per_sample[chan];
            sam = sine_table[(tone_phase[chan] >> 24) & 0xff];
	    put_sample (chan, a, sam);
	  }
  	  else {
	    
	    float fsam = dat ? amp16bit : (-amp16bit);

	    /* version 1.2 - added a low pass filter instead of square wave out. */

	    push_sample (fsam, raw[chan], lp_filter_size[chan]);
	    
	    resample[chan]++;
	    if (resample[chan] >= UPSAMPLE) {
	      int sam; 

	      sam = (int) convolve (raw[chan], lp_filter[chan], lp_filter_size[chan]);
	      resample[chan] = 0;
	      put_sample (chan, a, sam);
	    }
	  }

	  /* Enough for the bit time? */

	  bit_len_acc[chan] += ticks_per_sample[chan];

        } while (bit_len_acc[chan] < ticks_per_bit[chan]);

	bit_len_acc[chan] -= ticks_per_bit[chan];
}


static void put_sample (int chan, int a, int sam) {

        /* Ship out an audio sample. */

	assert (save_audio_config_p->adev[a].num_channels == 1 || save_audio_config_p->adev[a].num_channels == 2);

	/* Generalize to allow 8 bits someday? */

	assert (save_audio_config_p->adev[a].bits_per_sample == 16);

	if (sam < -32767) sam = -32767;
	else if (sam > 32767) sam = 32767;

	if (save_audio_config_p->adev[a].num_channels == 1) {

	  /* Mono */

          audio_put (a, sam & 0xff);
          audio_put (a, (sam >> 8) & 0xff);
 	}
	else {

	  if (chan == ADEVFIRSTCHAN(a)) {
	  
	    /* Stereo, left channel. */

            audio_put (a, sam & 0xff);
            audio_put (a, (sam >> 8) & 0xff);
 
            audio_put (a, 0);		
            audio_put (a, 0);
	  }
	  else { 

	    /* Stereo, right channel. */
	  
            audio_put (a, 0);		
            audio_put (a, 0);

            audio_put (a, sam & 0xff);
            audio_put (a, (sam >> 8) & 0xff);
	  }
	}
}



/*-------------------------------------------------------------------
 *
 * Name:        main
 *
 * Purpose:     Quick test program for above.
 *
 * Description: Compile like this for unit test:
 *
 *		gcc -Wall -DMAIN -o gen_tone_test gen_tone.c audio.c textcolor.c
 *
 *		gcc -Wall -DMAIN -o gen_tone_test.exe gen_tone.c audio_win.c textcolor.c -lwinmm
 *
 *--------------------------------------------------------------------*/


#if MAIN


int main ()
{
	int n;
	int chan1 = 0;
	int chan2 = 1;
	int r;
	struct audio_s my_audio_config;


/* to sound card */
/* one channel.  2 times:  one second of each tone. */

	memset (&my_audio_config, 0, sizeof(my_audio_config));
	strcpy (my_audio_config.adev[0].adevice_in, DEFAULT_ADEVICE);
	strcpy (my_audio_config.adev[0].adevice_out, DEFAULT_ADEVICE);

	audio_open (&my_audio_config);
	gen_tone_init (&my_audio_config, 100);

	for (r=0; r<2; r++) {

	  for (n=0; n<my_audio_config.baud[0] * 2 ; n++) {
 	    tone_gen_put_bit ( chan1, 1 );
	  }

	  for (n=0; n<my_audio_config.baud[0] * 2 ; n++) {
 	    tone_gen_put_bit ( chan1, 0 );
	  }
	}

	audio_close();

/* Now try stereo. */

	memset (&my_audio_config, 0, sizeof(my_audio_config));
	strcpy (my_audio_config.adev[0].adevice_in, DEFAULT_ADEVICE);
	strcpy (my_audio_config.adev[0].adevice_out, DEFAULT_ADEVICE);
	my_audio_config.adev[0].num_channels = 2;

	audio_open (&my_audio_config);
	gen_tone_init (&my_audio_config, 100);

	for (r=0; r<4; r++) {

	  for (n=0; n<my_audio_config.baud[0] * 2 ; n++) {
 	    tone_gen_put_bit ( chan1, 1 );
	  }

	  for (n=0; n<my_audio_config.baud[0] * 2 ; n++) {
 	    tone_gen_put_bit ( chan1, 0 );
	  }

	  for (n=0; n<my_audio_config.baud[0] * 2 ; n++) {
 	    tone_gen_put_bit ( chan2, 1 );
	  }

	  for (n=0; n<my_audio_config.baud[0] * 2 ; n++) {
 	    tone_gen_put_bit ( chan2, 0 );
	  }
	}

	audio_close();

	return(0);
}

#endif


/* end gen_tone.c */