rtl-trx.c

#include <stdio.h>
#include <stdint.h>
#include <unistd.h>
#include <sys/timerfd.h>
#include <rtl-sdr.h>
#include <pthread.h>
#include <signal.h>
#include <liquid/liquid.h>
#include <assert.h>
#include <string.h>
#include <stdlib.h>

#define BAUDOT_PREAMBLE_LENGTH 8
#include "baudot.h"

int if_freq = 3.6e6;
unsigned int center_freq = 1250e6;
int rx_gain = 500, tx_gain = 200;
int tone1 = 200, shift = 440;

// decimation from 2.4 MHz to 8 kHz/2
#define DECIM1 600


#define RTL_CHECK(x, y) { \
	ret = (x y); \
	if (ret < 0) { \
		fprintf(stderr, "Error: %s returned %d at %s:%d.\n", #x, ret, __FILE__, __LINE__); \
		goto err; \
	} \
}

pthread_t control_thrd=0;
rtlsdr_dev_t *dev = NULL;
int do_exit = 0;


static void sighandler(int signum) {
	(void)signum;
	do_exit = 1;
}


#define TXTEXT_LEN 500
#define TXBITS_LEN 512

static void *control(void *arg) {
	unsigned int txfreq, txfreq_tune, txfreq_tune0, txfreq_tune1, txfreq_prev;
	(void)arg;
	int ret;
	char txtext[TXTEXT_LEN];
	uint8_t txbits[TXBITS_LEN];
	
	int tfd=-1;

	for(;;) {
		int nbits, nbytes;
		rtlsdr_set_center_freq(dev, center_freq);
		rtlsdr_set_tuner_gain(dev, rx_gain);
		printf("Ready\n");

		char *r = fgets(txtext, TXTEXT_LEN, stdin);
		if(r == NULL) break;

		if(txtext[0] == 'F') {
			center_freq = atof(txtext+1);
			printf("Changing frequency to %d\n", center_freq);
			continue;
		}

		nbytes = baudot_from_ascii(txbits, TXBITS_LEN, txtext);
		nbits = nbytes*8;

		tfd = timerfd_create(CLOCK_MONOTONIC, 0);
		
		struct itimerspec tfd_ts;
		tfd_ts.it_value.tv_sec = 0;
		tfd_ts.it_value.tv_nsec = 1;
		tfd_ts.it_interval.tv_sec = 0;
		tfd_ts.it_interval.tv_nsec = 1e9 / 45.45 + 0.5;
		ret = timerfd_settime(tfd, 0, &tfd_ts, NULL);
		//printf("%d\n", ret);

		printf("Transmitting\n");
		RTL_CHECK(rtlsdr_set_tuner_gain,(dev, tx_gain));
		int bit_i = 0;
		uint64_t tfd_e = 0;

		txfreq = center_freq + tone1;
		txfreq_tune1 = txfreq / 4 - if_freq;
		txfreq = center_freq + tone1 - shift;
		txfreq_tune0 = txfreq / 4 - if_freq;
		txfreq_prev = 0;

		ret = read(tfd, &tfd_e, sizeof(uint64_t));
		while(bit_i < nbits) {
			if(txbits[bit_i / 8] & (1<<(7&bit_i)))
				txfreq_tune = txfreq_tune1;
			else
				txfreq_tune = txfreq_tune0;
			if(txfreq_tune != txfreq_prev)
				RTL_CHECK(rtlsdr_set_center_freq,(dev, txfreq_tune));
			txfreq_prev = txfreq_tune;

			ret = read(tfd, &tfd_e, sizeof(uint64_t));
			if(ret < 0) break;
			if(tfd_e > 1)
				printf("Warning: missed %ld bits\n", tfd_e-1);
			/* read from timerfd returns the number of timer
			   expirations. If we have missed some number of these,
			   we'll skip the same number of bits to keep timing
			   correct. */
			bit_i += tfd_e;

		}
		err:
		if(tfd > 0)
			close(tfd);
		tfd = -1;
	}

	do_exit = 1;
	return NULL;
}


float complex decim1[DECIM1];
msresamp_crcf decim1_q;
firhilbf hilbert_q;
int audiopipe = 3;
int outsamples = 0;

#define DECIM1_BUF 8192
#define DECIM1_OUTBUF (DECIM1_BUF/DECIM1 + 1)
static void rtlsdr_callback(unsigned char *buf, uint32_t len, void *arg) {
	(void)arg;
	float complex dec_in[DECIM1_BUF], dec_out[DECIM1_OUTBUF];
	float audio_out[2*DECIM1_OUTBUF];
	unsigned int dec_in_n, i, num_out=0;
	int ret, bytes_out;
	float audiogain = 0.1;
	if(do_exit) {
		printf("Canceling\n");
		rtlsdr_cancel_async(dev);
		return;
	}

	dec_in_n = len/2;
	assert(dec_in_n <= DECIM1_BUF);
	for(i = 0; i < dec_in_n; i++) {
		dec_in[i] = ((float)buf[2*i] - 127.4f) + I*((float)buf[2*i+1] - 127.4f);
	}

	msresamp_crcf_execute(decim1_q, dec_in, dec_in_n, dec_out, &num_out);
	assert(num_out <= DECIM1_OUTBUF);

	for(i = 0; i < num_out; i++) {
		float complex in = dec_out[i];

		// hilbert transform seems to swap halves of spectrum, fix it here:
		if(outsamples & 1)
			in = -audiogain*in;
		else
			in = audiogain*in;

		firhilbf_interp_execute(hilbert_q, in, audio_out + 2*i);
		outsamples++;
	}
	bytes_out = 2*num_out*sizeof(float);
	ret = write(audiopipe, audio_out, bytes_out);
	if(ret != bytes_out)
		printf("No audio pipe?\n");
}


int main() {
	int idx = 0;
	int sample_rate = 2.4e6;
	int blocksize = DECIM1_BUF*2;

	int ret;

	struct sigaction sigact;

	// setup signals
	sigact.sa_handler = sighandler;
	sigemptyset(&sigact.sa_mask);
	sigact.sa_flags = 0;
	sigaction(SIGINT, &sigact, NULL);
	sigaction(SIGTERM, &sigact, NULL);
	sigaction(SIGQUIT, &sigact, NULL);
	sigaction(SIGPIPE, &sigact, NULL);

	// initialize liquid-dsp
	decim1_q = msresamp_crcf_create(1.0/DECIM1, 60.0);
	hilbert_q = firhilbf_create(50, 60.0);


	// initialize rtl-sdr
	RTL_CHECK(rtlsdr_open,(&dev, idx));
	RTL_CHECK(rtlsdr_set_sample_rate,(dev, sample_rate));
	RTL_CHECK(rtlsdr_set_dithering,(dev, 0));
	RTL_CHECK(rtlsdr_set_if_freq,(dev, if_freq));
	RTL_CHECK(rtlsdr_set_center_freq,(dev, center_freq));
	RTL_CHECK(rtlsdr_set_tuner_gain_mode,(dev, 1));
	RTL_CHECK(rtlsdr_set_tuner_gain,(dev, rx_gain));

	// start
	pthread_create(&control_thrd, 0, control, NULL);

	RTL_CHECK(rtlsdr_reset_buffer,(dev));
	RTL_CHECK(rtlsdr_read_async,(dev, rtlsdr_callback, NULL, 0, blocksize));

	err:
	if(control_thrd)
		pthread_kill(control_thrd, SIGTERM);
	
	return 0;
}