From e82d475b7bbb2e3ba0388cad069eedf46f4ae363 Mon Sep 17 00:00:00 2001
From: ZoRo <dos21h@gmail.com>
Date: Sat, 19 Feb 2022 21:51:49 +0000
Subject: Initial

---
 src/rtl_adsb.c | 507 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 507 insertions(+)
 create mode 100644 src/rtl_adsb.c

(limited to 'src/rtl_adsb.c')

diff --git a/src/rtl_adsb.c b/src/rtl_adsb.c
new file mode 100644
index 0000000..7aea8dd
--- /dev/null
+++ b/src/rtl_adsb.c
@@ -0,0 +1,507 @@
+/*
+ * rtl-sdr, turns your Realtek RTL2832 based DVB dongle into a SDR receiver
+ * Copyright (C) 2012 by Steve Markgraf <steve@steve-m.de>
+ * Copyright (C) 2012 by Hoernchen <la@tfc-server.de>
+ * Copyright (C) 2012 by Kyle Keen <keenerd@gmail.com>
+ * Copyright (C) 2012 by Youssef Touil <youssef@sdrsharp.com>
+ * Copyright (C) 2012 by Ian Gilmour <ian@sdrsharp.com>
+ *
+ * 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 <errno.h>
+#include <signal.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+
+#ifndef _WIN32
+#include <unistd.h>
+#else
+#include <windows.h>
+#include <fcntl.h>
+#include <io.h>
+#include "getopt/getopt.h"
+#endif
+
+#include <pthread.h>
+#include <libusb.h>
+
+#include "rtl-sdr.h"
+#include "convenience/convenience.h"
+
+#ifdef _WIN32
+#define sleep Sleep
+#if defined(_MSC_VER) && (_MSC_VER < 1800)
+#define round(x) (x > 0.0 ? floor(x + 0.5): ceil(x - 0.5))
+#endif
+#endif
+
+#define ADSB_RATE			2000000
+#define ADSB_FREQ			1090000000
+#define DEFAULT_ASYNC_BUF_NUMBER	12
+#define DEFAULT_BUF_LENGTH		(16 * 16384)
+#define AUTO_GAIN			-100
+
+#define MESSAGEGO    253
+#define OVERWRITE    254
+#define BADSAMPLE    255
+
+static pthread_t demod_thread;
+static pthread_cond_t ready;
+static pthread_mutex_t ready_m;
+static volatile int do_exit = 0;
+static rtlsdr_dev_t *dev = NULL;
+
+uint16_t squares[256];
+
+/* todo, bundle these up in a struct */
+uint8_t *buffer;  /* also abused for uint16_t */
+int verbose_output = 0;
+int short_output = 0;
+int quality = 10;
+int allowed_errors = 5;
+FILE *file;
+int adsb_frame[14];
+#define preamble_len		16
+#define long_frame		112
+#define short_frame		56
+
+/* signals are not threadsafe by default */
+#define safe_cond_signal(n, m) pthread_mutex_lock(m); pthread_cond_signal(n); pthread_mutex_unlock(m)
+#define safe_cond_wait(n, m) pthread_mutex_lock(m); pthread_cond_wait(n, m); pthread_mutex_unlock(m)
+
+void usage(void)
+{
+	fprintf(stderr,
+		"rtl_adsb, a simple ADS-B decoder\n\n"
+		"Use:\trtl_adsb [-R] [-g gain] [-p ppm] [output file]\n"
+		"\t[-d device_index (default: 0)]\n"
+		"\t[-V verbove output (default: off)]\n"
+		"\t[-S show short frames (default: off)]\n"
+		"\t[-Q quality (0: no sanity checks, 0.5: half bit, 1: one bit (default), 2: two bits)]\n"
+		"\t[-e allowed_errors (default: 5)]\n"
+		"\t[-g tuner_gain (default: automatic)]\n"
+		"\t[-p ppm_error (default: 0)]\n"
+		"\t[-T enable bias-T on GPIO PIN 0 (works for rtl-sdr.com v3 dongles)]\n"
+		"\tfilename (a '-' dumps samples to stdout)\n"
+		"\t (omitting the filename also uses stdout)\n\n"
+		"Streaming with netcat:\n"
+		"\trtl_adsb | netcat -lp 8080\n"
+		"\twhile true; do rtl_adsb | nc -lp 8080; done\n"
+		"Streaming with socat:\n"
+		"\trtl_adsb | socat -u - TCP4:sdrsharp.com:47806\n"
+		"\n");
+	exit(1);
+}
+
+#ifdef _WIN32
+BOOL WINAPI
+sighandler(int signum)
+{
+	if (CTRL_C_EVENT == signum) {
+		fprintf(stderr, "Signal caught, exiting!\n");
+		do_exit = 1;
+		rtlsdr_cancel_async(dev);
+		return TRUE;
+	}
+	return FALSE;
+}
+#else
+static void sighandler(int signum)
+{
+	fprintf(stderr, "Signal caught, exiting!\n");
+	do_exit = 1;
+	rtlsdr_cancel_async(dev);
+}
+#endif
+
+void display(int *frame, int len)
+{
+	int i, df;
+	if (!short_output && len <= short_frame) {
+		return;}
+	df = (frame[0] >> 3) & 0x1f;
+	if (quality == 0 && !(df==11 || df==17 || df==18 || df==19)) {
+		return;}
+	fprintf(file, "*");
+	for (i=0; i<((len+7)/8); i++) {
+		fprintf(file, "%02x", frame[i]);}
+	fprintf(file, ";\r\n");
+	if (!verbose_output) {
+		return;}
+	fprintf(file, "DF=%i CA=%i\n", df, frame[0] & 0x07);
+	fprintf(file, "ICAO Address=%06x\n", frame[1] << 16 | frame[2] << 8 | frame[3]);
+	if (len <= short_frame) {
+		return;}
+	fprintf(file, "PI=0x%06x\n",  frame[11] << 16 | frame[12] << 8 | frame[13]);
+	fprintf(file, "Type Code=%i S.Type/Ant.=%x\n", (frame[4] >> 3) & 0x1f, frame[4] & 0x07);
+	fprintf(file, "--------------\n");
+}
+
+int abs8(int x)
+/* do not subtract 127 from the raw iq, this handles it */
+{
+	if (x >= 127) {
+		return x - 127;}
+	return 127 - x;
+}
+
+void squares_precompute(void)
+/* equiv to abs(x-128) ^ 2 */
+{
+	int i, j;
+	// todo, check if this LUT is actually any faster
+	for (i=0; i<256; i++) {
+		j = abs8(i);
+		squares[i] = (uint16_t)(j*j);
+	}
+}
+
+int magnitute(uint8_t *buf, int len)
+/* takes i/q, changes buf in place (16 bit), returns new len (16 bit) */
+{
+	int i;
+	uint16_t *m;
+	for (i=0; i<len; i+=2) {
+		m = (uint16_t*)(&buf[i]);
+		*m = squares[buf[i]] + squares[buf[i+1]];
+	}
+	return len/2;
+}
+
+static inline uint16_t single_manchester(uint16_t a, uint16_t b, uint16_t c, uint16_t d)
+/* takes 4 consecutive real samples, return 0 or 1, BADSAMPLE on error */
+{
+	int bit, bit_p;
+	bit_p = a > b;
+	bit   = c > d;
+
+	if (quality == 0) {
+		return bit;}
+
+	if (quality == 5) {
+		if ( bit &&  bit_p && b > c) {
+			return BADSAMPLE;}
+		if (!bit && !bit_p && b < c) {
+			return BADSAMPLE;}
+		return bit;
+	}
+
+	if (quality == 10) {
+		if ( bit &&  bit_p && c > b) {
+			return 1;}
+		if ( bit && !bit_p && d < b) {
+			return 1;}
+		if (!bit &&  bit_p && d > b) {
+			return 0;}
+		if (!bit && !bit_p && c < b) {
+			return 0;}
+		return BADSAMPLE;
+	}
+
+	if ( bit &&  bit_p && c > b && d < a) {
+		return 1;}
+	if ( bit && !bit_p && c > a && d < b) {
+		return 1;}
+	if (!bit &&  bit_p && c < a && d > b) {
+		return 0;}
+	if (!bit && !bit_p && c < b && d > a) {
+		return 0;}
+	return BADSAMPLE;
+}
+
+static inline uint16_t min16(uint16_t a, uint16_t b)
+{
+	return a<b ? a : b;
+}
+
+static inline uint16_t max16(uint16_t a, uint16_t b)
+{
+	return a>b ? a : b;
+}
+
+static inline int preamble(uint16_t *buf, int i)
+/* returns 0/1 for preamble at index i */
+{
+	int i2;
+	uint16_t low  = 0;
+	uint16_t high = 65535;
+	for (i2=0; i2<preamble_len; i2++) {
+		switch (i2) {
+			case 0:
+			case 2:
+			case 7:
+			case 9:
+				//high = min16(high, buf[i+i2]);
+				high = buf[i+i2];
+				break;
+			default:
+				//low  = max16(low,  buf[i+i2]);
+				low = buf[i+i2];
+				break;
+		}
+		if (high <= low) {
+			return 0;}
+	}
+	return 1;
+}
+
+void manchester(uint16_t *buf, int len)
+/* overwrites magnitude buffer with valid bits (BADSAMPLE on errors) */
+{
+	/* a and b hold old values to verify local manchester */
+	uint16_t a=0, b=0;
+	uint16_t bit;
+	int i, i2, start, errors;
+	int maximum_i = len - 1;        // len-1 since we look at i and i+1
+	// todo, allow wrap across buffers
+	i = 0;
+	while (i < maximum_i) {
+		/* find preamble */
+		for ( ; i < (len - preamble_len); i++) {
+			if (!preamble(buf, i)) {
+				continue;}
+			a = buf[i];
+			b = buf[i+1];
+			for (i2=0; i2<preamble_len; i2++) {
+				buf[i+i2] = MESSAGEGO;}
+			i += preamble_len;
+			break;
+		}
+		i2 = start = i;
+		errors = 0;
+		/* mark bits until encoding breaks */
+		for ( ; i < maximum_i; i+=2, i2++) {
+			bit = single_manchester(a, b, buf[i], buf[i+1]);
+			a = buf[i];
+			b = buf[i+1];
+			if (bit == BADSAMPLE) {
+				errors += 1;
+				if (errors > allowed_errors) {
+					buf[i2] = BADSAMPLE;
+					break;
+				} else {
+					bit = a > b;
+					/* these don't have to match the bit */
+					a = 0;
+					b = 65535;
+				}
+			}
+			buf[i] = buf[i+1] = OVERWRITE;
+			buf[i2] = bit;
+		}
+	}
+}
+
+void messages(uint16_t *buf, int len)
+{
+	int i, data_i, index, shift, frame_len;
+	// todo, allow wrap across buffers
+	for (i=0; i<len; i++) {
+		if (buf[i] > 1) {
+			continue;}
+		frame_len = long_frame;
+		data_i = 0;
+		for (index=0; index<14; index++) {
+			adsb_frame[index] = 0;}
+		for(; i<len && buf[i]<=1 && data_i<frame_len; i++, data_i++) {
+			if (buf[i]) {
+				index = data_i / 8;
+				shift = 7 - (data_i % 8);
+				adsb_frame[index] |= (uint8_t)(1<<shift);
+			}
+			if (data_i == 7) {
+				if (adsb_frame[0] == 0) {
+				    break;}
+				if (adsb_frame[0] & 0x80) {
+					frame_len = long_frame;}
+				else {
+					frame_len = short_frame;}
+			}
+		}
+		if (data_i < (frame_len-1)) {
+			continue;}
+		display(adsb_frame, frame_len);
+		fflush(file);
+	}
+}
+
+static void rtlsdr_callback(unsigned char *buf, uint32_t len, void *ctx)
+{
+	if (do_exit) {
+		return;}
+	memcpy(buffer, buf, len);
+	safe_cond_signal(&ready, &ready_m);
+}
+
+static void *demod_thread_fn(void *arg)
+{
+	int len;
+	while (!do_exit) {
+		safe_cond_wait(&ready, &ready_m);
+		len = magnitute(buffer, DEFAULT_BUF_LENGTH);
+		manchester((uint16_t*)buffer, len);
+		messages((uint16_t*)buffer, len);
+	}
+	rtlsdr_cancel_async(dev);
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+#ifndef _WIN32
+	struct sigaction sigact;
+#endif
+	char *filename = NULL;
+	int r, opt;
+	int gain = AUTO_GAIN; /* tenths of a dB */
+	int dev_index = 0;
+	int dev_given = 0;
+	int ppm_error = 0;
+	int enable_biastee = 0;
+	pthread_cond_init(&ready, NULL);
+	pthread_mutex_init(&ready_m, NULL);
+	squares_precompute();
+
+	while ((opt = getopt(argc, argv, "d:g:p:e:Q:VST")) != -1)
+	{
+		switch (opt) {
+		case 'd':
+			dev_index = verbose_device_search(optarg);
+			dev_given = 1;
+			break;
+		case 'g':
+			gain = (int)(atof(optarg) * 10);
+			break;
+		case 'p':
+			ppm_error = atoi(optarg);
+			break;
+		case 'V':
+			verbose_output = 1;
+			break;
+		case 'S':
+			short_output = 1;
+			break;
+		case 'e':
+			allowed_errors = atoi(optarg);
+			break;
+		case 'Q':
+			quality = (int)(atof(optarg) * 10);
+			break;
+		case 'T':
+			enable_biastee = 1;
+			break;
+		default:
+			usage();
+			return 0;
+		}
+	}
+
+	if (argc <= optind) {
+		filename = "-";
+	} else {
+		filename = argv[optind];
+	}
+
+	buffer = malloc(DEFAULT_BUF_LENGTH * sizeof(uint8_t));
+
+	if (!dev_given) {
+		dev_index = verbose_device_search("0");
+	}
+
+	if (dev_index < 0) {
+		exit(1);
+	}
+
+	r = rtlsdr_open(&dev, (uint32_t)dev_index);
+	if (r < 0) {
+		fprintf(stderr, "Failed to open rtlsdr device #%d.\n", dev_index);
+		exit(1);
+	}
+#ifndef _WIN32
+	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);
+#else
+	SetConsoleCtrlHandler( (PHANDLER_ROUTINE) sighandler, TRUE );
+#endif
+
+	if (strcmp(filename, "-") == 0) { /* Write samples to stdout */
+		file = stdout;
+		setvbuf(stdout, NULL, _IONBF, 0);
+#ifdef _WIN32
+		_setmode(_fileno(file), _O_BINARY);
+#endif
+	} else {
+		file = fopen(filename, "wb");
+		if (!file) {
+			fprintf(stderr, "Failed to open %s\n", filename);
+			exit(1);
+		}
+	}
+
+	/* Set the tuner gain */
+	if (gain == AUTO_GAIN) {
+		verbose_auto_gain(dev);
+	} else {
+		gain = nearest_gain(dev, gain);
+		verbose_gain_set(dev, gain);
+	}
+
+	verbose_ppm_set(dev, ppm_error);
+	r = rtlsdr_set_agc_mode(dev, 1);
+
+	/* Set the tuner frequency */
+	verbose_set_frequency(dev, ADSB_FREQ);
+
+	/* Set the sample rate */
+	verbose_set_sample_rate(dev, ADSB_RATE);
+
+	rtlsdr_set_bias_tee(dev, enable_biastee);
+	if (enable_biastee)
+		fprintf(stderr, "activated bias-T on GPIO PIN 0\n");
+
+	/* Reset endpoint before we start reading from it (mandatory) */
+	verbose_reset_buffer(dev);
+
+	pthread_create(&demod_thread, NULL, demod_thread_fn, (void *)(NULL));
+	rtlsdr_read_async(dev, rtlsdr_callback, (void *)(NULL),
+			      DEFAULT_ASYNC_BUF_NUMBER,
+			      DEFAULT_BUF_LENGTH);
+
+	if (do_exit) {
+		fprintf(stderr, "\nUser cancel, exiting...\n");}
+	else {
+		fprintf(stderr, "\nLibrary error %d, exiting...\n", r);}
+	rtlsdr_cancel_async(dev);
+	pthread_cancel(demod_thread);
+	pthread_join(demod_thread, NULL);
+	pthread_cond_destroy(&ready);
+	pthread_mutex_destroy(&ready_m);
+
+	if (file != stdout) {
+		fclose(file);}
+
+	rtlsdr_close(dev);
+	free(buffer);
+	return r >= 0 ? r : -r;
+}
+
-- 
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