path: root/src/fl2k_fm.c

/*
 * osmo-fl2k, turns FL2000-based USB 3.0 to VGA adapters into
 * low cost DACs
 *
 * Copyright (C) 2016-2018 by Steve Markgraf <steve@steve-m.de>
 *
 * based on FM modulator code from VGASIG:
 * Copyright (C) 2009 by Bartek Kania <mbk@gnarf.org>
 *
 * SPDX-License-Identifier: GPL-2.0+
 *
 * 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/>.
 */

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <string.h>
#include <errno.h>

#ifndef _WIN32
#include <unistd.h>
#include <fcntl.h>
#include <getopt.h>
#else
#include <windows.h>
#include <io.h>
#include <fcntl.h>
#include "getopt/getopt.h"
#endif

#include <math.h>
#include <pthread.h>

#include "osmo-fl2k.h"
#include "rds_mod.h"

#define BUFFER_SAMPLES_SHIFT	16
#define BUFFER_SAMPLES		(1 << BUFFER_SAMPLES_SHIFT)
#define BUFFER_SAMPLES_MASK	((1 << BUFFER_SAMPLES_SHIFT)-1)

#define AUDIO_BUF_SIZE		1024

fl2k_dev_t *dev = NULL;
int do_exit = 0;

pthread_t fm_thread;
pthread_mutex_t cb_mutex;
pthread_mutex_t fm_mutex;
pthread_cond_t cb_cond;
pthread_cond_t fm_cond;

FILE *file;
int8_t *txbuf = NULL;
int8_t *fmbuf = NULL;
int8_t *buf1 = NULL;
int8_t *buf2 = NULL;

uint32_t samp_rate = 100000000;

/* default signal parameters */
#define PILOT_FREQ	19000	/* In Hz */
#define STEREO_CARRIER	38000	/* In Hz */

int delta_freq = 75000;
int carrier_freq = 97000000;
int carrier_per_signal;
int input_freq = 44100;
int stereo_flag = 0;
int rds_flag = 0;

double *freqbuf; 
double *slopebuf; 
int writepos, readpos;

void usage(void)
{
	fprintf(stderr,
		"fl2k_fm, an FM modulator for FL2K VGA dongles\n\n"
		"Usage:"
		"\t[-d device index (default: 0)]\n"
		"\t[-c carrier frequency (default: 9.7 MHz)]\n"
		"\t[-f FM deviation (default: 75000 Hz, WBFM)]\n"
		"\t[-i input audio sample rate (default: 44100 Hz for mono FM)]\n"
		"\t[-s samplerate in Hz (default: 100 MS/s)]\n"
		"\t[--rds (enables RDS, forces audio sample rate to 228 kHz)]\n"
		"\t[--stereo (enables stereo, requires audio sample rate >= 114 kHz)]\n"
		"\tfilename (use '-' to read from stdin)\n\n"
	);
	exit(1);
}

#ifdef _WIN32
BOOL WINAPI
sighandler(int signum)
{
	if (CTRL_C_EVENT == signum) {
		fprintf(stderr, "Signal caught, exiting!\n");
		fl2k_stop_tx(dev);
		do_exit = 1;
		pthread_cond_signal(&fm_cond);
		return TRUE;
	}
	return FALSE;
}
#else
static void sighandler(int signum)
{
	fprintf(stderr, "Signal caught, exiting!\n");
	fl2k_stop_tx(dev);
	do_exit = 1;
	pthread_cond_signal(&fm_cond);
}
#endif

/* DDS Functions */

#ifndef M_PI
# define M_PI		3.14159265358979323846	/* pi */
# define M_PI_2		1.57079632679489661923	/* pi/2 */
# define M_PI_4		0.78539816339744830962	/* pi/4 */
# define M_1_PI		0.31830988618379067154	/* 1/pi */
# define M_2_PI		0.63661977236758134308	/* 2/pi */
#endif
#define DDS_2PI		(M_PI * 2)		/* 2 * Pi */
#define DDS_3PI2	(M_PI_2 * 3)		/* 3/2 * pi */

#define SIN_TABLE_ORDER	8
#define SIN_TABLE_SHIFT	(32 - SIN_TABLE_ORDER)
#define SIN_TABLE_LEN	(1 << SIN_TABLE_ORDER)
#define ANG_INCR	(0xffffffff / DDS_2PI)

int8_t sine_table[SIN_TABLE_LEN];
int sine_table_init = 0;

typedef struct {
	double sample_freq;
	double freq;
	double fslope;
	unsigned long int phase;
	unsigned long int phase_step;
	unsigned long int phase_slope;
} dds_t;

static inline void dds_setphase(dds_t *dds, double phase)
{
	dds->phase = phase * ANG_INCR;
}

static inline double dds_getphase(dds_t *dds)
{
	return dds->phase / ANG_INCR;
}

static inline void dds_set_freq(dds_t *dds, double freq, double fslope)
{
	dds->fslope = fslope;
	dds->phase_step = (freq / dds->sample_freq) * 2 * M_PI * ANG_INCR;

	/* The slope parameter is used with the FM modulator to create
	 * a simple but very fast and effective interpolation filter.
	 * See the fm modulator for details */
	dds->freq = freq;
	dds->phase_slope = (fslope / dds->sample_freq) * 2 * M_PI * ANG_INCR;
}

dds_t dds_init(double sample_freq, double freq, double phase)
{
	dds_t dds;
	int i;

	dds.sample_freq = sample_freq;
	dds.phase = phase * ANG_INCR;
	dds_set_freq(&dds, freq, 0);

	/* Initialize sine table, prescaled for 8 bit signed integer */
	if (!sine_table_init) {
		double incr = 1.0 / (double)SIN_TABLE_LEN;
		for (i = 0; i < SIN_TABLE_LEN; i++)
			sine_table[i] = sin(incr * i * DDS_2PI) * 127;

		sine_table_init = 1;
	}

	return dds;
}

static inline int8_t dds_real(dds_t *dds)
{
	int tmp;

	tmp = dds->phase >> SIN_TABLE_SHIFT;
	dds->phase += dds->phase_step;
	dds->phase &= 0xffffffff;

	dds->phase_step += dds->phase_slope;

	return sine_table[tmp];
}

static inline void dds_real_buf(dds_t *dds, int8_t *buf, int count)
{
	int i;
	for (i = 0; i < count; i++)
		buf[i] = dds_real(dds);
}

/* Signal generation and some helpers */

/* Generate the radio signal using the pre-calculated frequency information
 * in the freq buffer */
static void *fm_worker(void *arg)
{
	register double freq;
	register double tmp;
	dds_t carrier;
	int8_t *tmp_ptr;
	uint32_t len = 0;
	uint32_t readlen, remaining;
	int buf_prefilled = 0;

	/* Prepare the oscillators */
	carrier = dds_init(samp_rate, carrier_freq, 0);

	while (!do_exit) {
		dds_set_freq(&carrier, freqbuf[readpos], slopebuf[readpos]);
		readpos++;
		readpos &= BUFFER_SAMPLES_MASK;

		/* check if we reach the end of the buffer */
		if ((len + carrier_per_signal) > FL2K_BUF_LEN) {
			readlen = FL2K_BUF_LEN - len;
			remaining = carrier_per_signal - readlen;
			dds_real_buf(&carrier, &fmbuf[len], readlen);

			if (buf_prefilled) {
				/* swap buffers */
				tmp_ptr = fmbuf;
				fmbuf = txbuf;
				txbuf = tmp_ptr;
				pthread_cond_wait(&cb_cond, &cb_mutex);
			}

			dds_real_buf(&carrier, fmbuf, remaining);
			len = remaining;

			buf_prefilled = 1;
		} else {
			dds_real_buf(&carrier, &fmbuf[len], carrier_per_signal);
			len += carrier_per_signal;
		}

		pthread_cond_signal(&fm_cond);
	}

	pthread_exit(NULL);
}

static inline int writelen(int maxlen)
{
	int rp = readpos;
	int len;
	int r;

	if (rp < writepos)
		rp += BUFFER_SAMPLES;

	len = rp - writepos;

	r = len > maxlen ? maxlen : len;

	return r;
}

static inline double modulate_sample(int lastwritepos, double lastfreq, double sample)
{
	double freq, slope;

	/* Calculate modulator frequency at this point to lessen
	 * the calculations needed in the signal generator */
	freq = sample * delta_freq;
	freq += carrier_freq;

	/* What we do here is calculate a linear "slope" from
	the previous sample to this one. This is then used by
	the modulator to gently increase/decrease the frequency
	with each sample without the need to recalculate
	the dds parameters. In fact this gives us a very
	efficient and pretty good interpolation filter. */
	slope = freq - lastfreq;
	slope /= carrier_per_signal;
	slopebuf[lastwritepos] = slope;
	freqbuf[writepos] = freq;

	return freq;
}

void fm_modulator_mono(int use_rds)
{
	unsigned int i;
	size_t len;
	double freq;
	double lastfreq = carrier_freq;
	int16_t audio_buf[AUDIO_BUF_SIZE];
	uint32_t lastwritepos = writepos;
	double sample;
	double rds_samples[AUDIO_BUF_SIZE];

	while (!do_exit) {
		len = writelen(AUDIO_BUF_SIZE);
		if (len > 1) {
			len = fread(audio_buf, 2, len, file);

			if (len == 0)
				do_exit = 1;

			if (use_rds)
				get_rds_samples(rds_samples, len);

			for (i = 0; i < len; i++) {
				sample = audio_buf[i] / 32767.0;

				if (use_rds) {
					sample *= 4;
					sample += rds_samples[i];
					sample /= 5;
				}

				/* Modulate and buffer the sample */
				lastfreq = modulate_sample(lastwritepos, lastfreq, sample);
				lastwritepos = writepos++;
				writepos %= BUFFER_SAMPLES;
			}
		} else {
			pthread_cond_wait(&fm_cond, &fm_mutex);
		}
	}
}

void fm_modulator_stereo(int use_rds)
{
	unsigned int i;
	size_t len, sample_cnt;
	double freq;
	double lastfreq = carrier_freq;
	int16_t audio_buf[AUDIO_BUF_SIZE];
	uint32_t lastwritepos = writepos;

	dds_t pilot, stereo;
	double L, R, LpR, LmR, sample;
	double rds_samples[AUDIO_BUF_SIZE];

	/* Prepare stereo carriers */
	pilot = dds_init(input_freq, PILOT_FREQ, 0);
	stereo = dds_init(input_freq, STEREO_CARRIER, 0);

	while (!do_exit) {
		len = writelen(AUDIO_BUF_SIZE);
		if (len > 1 && !(len % 2)) {
			len = fread(audio_buf, 2, len, file);

			if (len == 0)
				do_exit = 1;

			/* stereo => two audio samples per baseband sample */
			sample_cnt = len/2;

			if (use_rds)
				get_rds_samples(rds_samples, sample_cnt);

			for (i = 0; i < sample_cnt; i++) {
				/* Get samples for both channels, and calculate the 
				* mono (L+R) and the difference signal used to recreate
				* the stereo data (L-R). */
				L = audio_buf[i*2] / 32767.0;
				R = audio_buf[i*2+1] / 32767.0;
				LpR = (L + R) / 2;
				LmR = (L - R) / 2;

				/* Create a composite sample consisting of the mono
				* signal at baseband, a 19kHz pilot and a the difference
				* signal DSB-SC modulated on a 38kHz carrier */
				sample = 4.05 * LpR;					/* Mono signal */
				sample += 0.9 * (dds_real(&pilot)/127.0);		/* Pilot */
				sample += 4.05 * LmR * (dds_real(&stereo)/127.0);	/* DSB-SC stereo */

				if (use_rds) {
					/* add RDS signal */
					sample += rds_samples[i];

					/* Normalize so we get the signal within [-1, 1] */
					sample /= 10;
				} else {
					sample /= 9;
				}

				lastfreq = modulate_sample(lastwritepos, lastfreq, sample);

				lastwritepos = writepos++;
				writepos %= BUFFER_SAMPLES;
			}
		} else {
			pthread_cond_wait(&fm_cond, &fm_mutex);
		}
	}
}

void fl2k_callback(fl2k_data_info_t *data_info)
{
	if (data_info->device_error) {
		fprintf(stderr, "Device error, exiting.\n");
		do_exit = 1;
		pthread_cond_signal(&fm_cond);
	}

	pthread_cond_signal(&cb_cond);

	data_info->sampletype_signed = 1;
	data_info->r_buf = (char *)txbuf;
}

int main(int argc, char **argv)
{
	int r, opt;
	uint32_t buf_num = 0;
	int dev_index = 0;
	pthread_attr_t attr;
	char *filename = NULL;
	int option_index = 0;
	int input_freq_specified = 0;

#ifndef _WIN32
	struct sigaction sigact, sigign;
#endif

	static struct option long_options[] =
	{
		{"stereo", no_argument, &stereo_flag, 1},
		{"rds",    no_argument, &rds_flag,    1},
		{0, 0, 0, 0}
	};

	while (1) {
		opt = getopt_long(argc, argv, "d:c:f:i:s:", long_options, &option_index);

		/* end of options reached */
		if (opt == -1)
			break;

		switch (opt) {
		case 0:
			break;
		case 'd':
			dev_index = (uint32_t)atoi(optarg);
			break;
		case 'c':
			carrier_freq = (uint32_t)atof(optarg);
			break;
		case 'f':
			delta_freq = (uint32_t)atof(optarg);
			break;
		case 'i':
			input_freq = (uint32_t)atof(optarg);
			input_freq_specified = 1;
			break;
		case 's':
			samp_rate = (uint32_t)atof(optarg);
			break;
		default:
			usage();
			break;
		}
	}

	if (argc <= optind) {
		usage();
	} else {
		filename = argv[optind];
	}

	if (dev_index < 0) {
		exit(1);
	}

	if (rds_flag && input_freq_specified) {
		if (input_freq != RDS_MODULATOR_RATE) {
			fprintf(stderr, "RDS modulator only works with "
					"228 kHz audio sample rate!\n");
			exit(1);
		}
	} else if (rds_flag && !input_freq_specified) {
		input_freq = RDS_MODULATOR_RATE;
	}

	if (stereo_flag && input_freq < (RDS_MODULATOR_RATE/2)) {
		fprintf(stderr, "Audio sample rate needs to be at least "
				"114 kHz for stereo FM!\n");
		exit(1);
	}


	if (strcmp(filename, "-") == 0) { /* Read samples from stdin */
		file = stdin;
#ifdef _WIN32
		_setmode(_fileno(stdin), _O_BINARY);
#endif
	} else {
		file = fopen(filename, "rb");
		if (!file) {
			fprintf(stderr, "Failed to open %s\n", filename);
			return -ENOENT;
		}
	}

	/* allocate buffer */
	buf1 = malloc(FL2K_BUF_LEN);
	buf2 = malloc(FL2K_BUF_LEN);
	if (!buf1 || !buf2) {
		fprintf(stderr, "malloc error!\n");
		exit(1);
	}

	fmbuf = buf1;
	txbuf = buf2;

	/* Decoded audio */
	freqbuf = malloc(BUFFER_SAMPLES * sizeof(double));
	slopebuf = malloc(BUFFER_SAMPLES * sizeof(double));
	readpos = 0;
	writepos = 1;

	fprintf(stderr, "Samplerate:\t%3.2f MHz\n", (double)samp_rate/1000000);
	fprintf(stderr, "Carrier:\t%3.2f MHz\n", (double)carrier_freq/1000000);
	fprintf(stderr, "Frequencies:\t%3.2f MHz, %3.2f MHz\n", 
					(double)((samp_rate - carrier_freq) / 1000000.0),
					(double)((samp_rate + carrier_freq) / 1000000.0));

	pthread_mutex_init(&cb_mutex, NULL);
	pthread_mutex_init(&fm_mutex, NULL);
	pthread_cond_init(&cb_cond, NULL);
	pthread_cond_init(&fm_cond, NULL);
	pthread_attr_init(&attr);

	fl2k_open(&dev, (uint32_t)dev_index);
	if (NULL == dev) {
		fprintf(stderr, "Failed to open fl2k device #%d.\n", dev_index);
		goto out;
	}

	r = pthread_create(&fm_thread, &attr, fm_worker, NULL);
	if (r < 0) {
		fprintf(stderr, "Error spawning FM worker thread!\n");
		goto out;
	}

	pthread_attr_destroy(&attr);
	r = fl2k_start_tx(dev, fl2k_callback, NULL, 0);

	/* Set the sample rate */
	r = fl2k_set_sample_rate(dev, samp_rate);
	if (r < 0)
		fprintf(stderr, "WARNING: Failed to set sample rate. %d\n", r);

	/* read back actual frequency */
	samp_rate = fl2k_get_sample_rate(dev);

	/* Calculate needed constants */
	carrier_per_signal = samp_rate / input_freq;

	/* Set RDS parameters */
	set_rds_pi(0x0dac);
	set_rds_ps("fl2k_fm");
	set_rds_rt("VGA FM transmitter");

#ifndef _WIN32
	sigact.sa_handler = sighandler;
	sigemptyset(&sigact.sa_mask);
	sigact.sa_flags = 0;
	sigign.sa_handler = SIG_IGN;
	sigaction(SIGINT, &sigact, NULL);
	sigaction(SIGTERM, &sigact, NULL);
	sigaction(SIGQUIT, &sigact, NULL);
	sigaction(SIGPIPE, &sigign, NULL);
#else
	SetConsoleCtrlHandler( (PHANDLER_ROUTINE) sighandler, TRUE );
#endif

	if (stereo_flag) {
		fm_modulator_stereo(rds_flag);
	} else {
		if (rds_flag)
			fprintf(stderr, "Warning: RDS with mono (without 19 kHz pilot"
					" tone) doesn't work with all receivers!\n");

		fm_modulator_mono(rds_flag);
	}

out:
	fl2k_close(dev);

	if (file != stdin)
		fclose(file);

	free(freqbuf);
	free(slopebuf);
	free(buf1);
	free(buf2);

	return 0;
}