dump1090.c

/* M/de1090, a Mode S messages decoder for RTLSDR devices.
 * Copyright (C) 2017 by Jiang Wei <jiangwei0402@gmail.com>
 * Copyright (C) 2012 by Salvatore Sanfilippo <antirez@gmail.com>
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *  *  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *  *  Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <pthread.h>
#include <stdint.h>
#include <errno.h>
#include <unistd.h>
#include <math.h>
#include <sys/time.h>
#include <signal.h>
#include <fcntl.h>
#include <ctype.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/select.h>
#include <iio.h>
#include <ad9361.h>
#include "anet.h"
#include "incbin.h"

#define MODES_DEFAULT_RATE         2000000
#define MODES_DEFAULT_FREQ         1090000000
#define MODES_DEFAULT_WIDTH        1000
#define MODES_DEFAULT_HEIGHT       700
#define MODES_ASYNC_BUF_NUMBER     12
#define MODES_DATA_LEN             (16*16384)   /* 256k */
#define MODES_AUTO_GAIN            -100         /* Use automatic gain. */
#define MODES_MAX_GAIN             70       /* Use max available gain. */

#define MODES_PREAMBLE_US 8       /* microseconds */
#define MODES_LONG_MSG_BITS 112
#define MODES_SHORT_MSG_BITS 56
#define MODES_FULL_LEN (MODES_PREAMBLE_US+MODES_LONG_MSG_BITS)
#define MODES_LONG_MSG_BYTES (112/8)
#define MODES_SHORT_MSG_BYTES (56/8)

#define MODES_ICAO_CACHE_LEN 1024 /* Power of two required. */
#define MODES_ICAO_CACHE_TTL 60   /* Time to live of cached addresses. */
#define MODES_UNIT_FEET 0
#define MODES_UNIT_METERS 1

#define MODES_DEBUG_DEMOD (1<<0)
#define MODES_DEBUG_DEMODERR (1<<1)
#define MODES_DEBUG_BADCRC (1<<2)
#define MODES_DEBUG_GOODCRC (1<<3)
#define MODES_DEBUG_NOPREAMBLE (1<<4)
#define MODES_DEBUG_NET (1<<5)
#define MODES_DEBUG_JS (1<<6)

/* When debug is set to MODES_DEBUG_NOPREAMBLE, the first sample must be
 * at least greater than a given level for us to dump the signal. */
#define MODES_DEBUG_NOPREAMBLE_LEVEL 25

#define MODES_INTERACTIVE_REFRESH_TIME 250      /* Milliseconds */
#define MODES_INTERACTIVE_ROWS 15               /* Rows on screen */
#define MODES_INTERACTIVE_TTL 60                /* TTL before being removed */

#define MODES_NET_MAX_FD 1024
#define MODES_NET_OUTPUT_SBS_PORT 30003
#define MODES_NET_OUTPUT_RAW_PORT 30002
#define MODES_NET_INPUT_RAW_PORT 30001
#define MODES_NET_HTTP_PORT 8080
#define MODES_CLIENT_BUF_SIZE 1024
#define MODES_NET_SNDBUF_SIZE (1024*64)

#define MODES_NOTUSED(V) ((void) V)
INCBIN(html,"gmap.html");
/* Structure used to describe a networking client. */
struct client {
	int fd;         /* File descriptor. */
	int service;    /* TCP port the client is connected to. */
	char buf[MODES_CLIENT_BUF_SIZE + 1];    /* Read buffer. */
	int buflen;                         /* Amount of data on buffer. */
};

/* Structure used to describe an aircraft in iteractive mode. */
struct aircraft {
	uint32_t addr;      /* ICAO address */
	char hexaddr[7];    /* Printable ICAO address */
	char flight[9];     /* Flight number */
	int altitude;       /* Altitude */
	int speed;          /* Velocity computed from EW and NS components. */
	int track;          /* Angle of flight. */
	time_t seen;        /* Time at which the last packet was received. */
	long messages;      /* Number of Mode S messages received. */
	/* Encoded latitude and longitude as extracted by odd and even
	 * CPR encoded messages. */
	int odd_cprlat;
	int odd_cprlon;
	int even_cprlat;
	int even_cprlon;
	double lat, lon;    /* Coordinated obtained from CPR encoded data. */
	long long odd_cprtime, even_cprtime;
	struct aircraft *next; /* Next aircraft in our linked list. */
};

/* Program global state. */
struct {
	/* Internal state */
	pthread_t reader_thread;
	pthread_mutex_t data_mutex;     /* Mutex to synchronize buffer access. */
	pthread_cond_t data_cond;       /* Conditional variable associated. */
	unsigned char *data;            /* Raw IQ samples buffer */
	uint16_t *magnitude;            /* Magnitude vector */
	uint32_t data_len;              /* Buffer length. */
	int fd;                         /* --ifile option file descriptor. */
	int data_ready;                 /* Data ready to be processed. */
	uint32_t *icao_cache;           /* Recently seen ICAO addresses cache. */
	uint16_t *maglut;               /* I/Q -> Magnitude lookup table. */
	int exit;                       /* Exit from the main loop when true. */

	/* PLUTOSDR */
	int dev_index;
	int gain;
	int enable_agc;
	struct iio_context *ctx;
	struct iio_device *dev;
	long long freq;
	struct iio_channel *rx0_i;
	struct iio_channel *rx0_q;
	struct iio_buffer  *rxbuf;
	int stop;

	/* Networking */
	char aneterr[ANET_ERR_LEN];
	struct client *clients[MODES_NET_MAX_FD]; /* Our clients. */
	int maxfd;                      /* Greatest fd currently active. */
	int sbsos;                      /* SBS output listening socket. */
	int ros;                        /* Raw output listening socket. */
	int ris;                        /* Raw input listening socket. */
	int https;                      /* HTTP listening socket. */

	/* Configuration */
	char *filename;                 /* Input form file, --ifile option. */
	int fix_errors;                 /* Single bit error correction if true. */
	int check_crc;                  /* Only display messages with good CRC. */
	int raw;                        /* Raw output format. */
	int debug;                      /* Debugging mode. */
	int net;                        /* Enable networking. */
	int net_only;                   /* Enable just networking. */
	int interactive;                /* Interactive mode */
	int interactive_rows;           /* Interactive mode: max number of rows. */
	int interactive_ttl;            /* Interactive mode: TTL before deletion. */
	int stats;                      /* Print stats at exit in --ifile mode. */
	int onlyaddr;                   /* Print only ICAO addresses. */
	int metric;                     /* Use metric units. */
	int aggressive;                 /* Aggressive detection algorithm. */

	/* Interactive mode */
	struct aircraft *aircrafts;
	long long interactive_last_update;  /* Last screen update in milliseconds */

	/* Statistics */
	long long stat_valid_preamble;
	long long stat_demodulated;
	long long stat_goodcrc;
	long long stat_badcrc;
	long long stat_fixed;
	long long stat_single_bit_fix;
	long long stat_two_bits_fix;
	long long stat_http_requests;
	long long stat_sbs_connections;
	long long stat_out_of_phase;
} Modes;

/* The struct we use to store information about a decoded message. */
struct modesMessage {
	/* Generic fields */
	unsigned char msg[MODES_LONG_MSG_BYTES]; /* Binary message. */
	int msgbits;                /* Number of bits in message */
	int msgtype;                /* Downlink format # */
	int crcok;                  /* True if CRC was valid */
	uint32_t crc;               /* Message CRC */
	int errorbit;               /* Bit corrected. -1 if no bit corrected. */
	int aa1, aa2, aa3;          /* ICAO Address bytes 1 2 and 3 */
	int phase_corrected;        /* True if phase correction was applied. */

	/* DF 11 */
	int ca;                     /* Responder capabilities. */

	/* DF 17 */
	int metype;                 /* Extended squitter message type. */
	int mesub;                  /* Extended squitter message subtype. */
	int heading_is_valid;
	int heading;
	int aircraft_type;
	int fflag;                  /* 1 = Odd, 0 = Even CPR message. */
	int tflag;                  /* UTC synchronized? */
	int raw_latitude;           /* Non decoded latitude */
	int raw_longitude;          /* Non decoded longitude */
	char flight[9];             /* 8 chars flight number. */
	int ew_dir;                 /* 0 = East, 1 = West. */
	int ew_velocity;            /* E/W velocity. */
	int ns_dir;                 /* 0 = North, 1 = South. */
	int ns_velocity;            /* N/S velocity. */
	int vert_rate_source;       /* Vertical rate source. */
	int vert_rate_sign;         /* Vertical rate sign. */
	int vert_rate;              /* Vertical rate. */
	int velocity;               /* Computed from EW and NS velocity. */

	/* DF4, DF5, DF20, DF21 */
	int fs;                     /* Flight status for DF4,5,20,21 */
	int dr;                     /* Request extraction of downlink request. */
	int um;                     /* Request extraction of downlink request. */
	int identity;               /* 13 bits identity (Squawk). */

	/* Fields used by multiple message types. */
	int altitude, unit;
};

void interactiveShowData(void);
struct aircraft* interactiveReceiveData(struct modesMessage *mm);
void modesSendRawOutput(struct modesMessage *mm);
void modesSendSBSOutput(struct modesMessage *mm, struct aircraft *a);
void useModesMessage(struct modesMessage *mm);
int fixSingleBitErrors(unsigned char *msg, int bits);
int fixTwoBitsErrors(unsigned char *msg, int bits);
int modesMessageLenByType(int type);
void sigWinchCallback();
int getTermRows();

/* ============================= Utility functions ========================== */

static long long mstime(void) {
	struct timeval tv;
	long long mst;

	gettimeofday(&tv, NULL);
	mst = ((long long)tv.tv_sec) * 1000;
	mst += tv.tv_usec / 1000;
	return mst;
}

/* =============================== Initialization =========================== */

void modesInitConfig(void) {
	Modes.gain = MODES_AUTO_GAIN;
	Modes.dev_index = 0;
	Modes.enable_agc = 1;
	Modes.freq = MODES_DEFAULT_FREQ;
	Modes.filename = NULL;
	Modes.fix_errors = 1;
	Modes.check_crc = 1;
	Modes.raw = 0;
	Modes.net = 0;
	Modes.net_only = 0;
	Modes.onlyaddr = 0;
	Modes.debug = 0;
	Modes.interactive = 0;
	Modes.interactive_rows = MODES_INTERACTIVE_ROWS;
	Modes.interactive_ttl = MODES_INTERACTIVE_TTL;
	Modes.aggressive = 0;
	Modes.interactive_rows = getTermRows();
}

void modesInit(void) {
	int i, q;

	pthread_mutex_init(&Modes.data_mutex, NULL);
	pthread_cond_init(&Modes.data_cond, NULL);
	/* We add a full message minus a final bit to the length, so that we
	 * can carry the remaining part of the buffer that we can't process
	 * in the message detection loop, back at the start of the next data
	 * to process. This way we are able to also detect messages crossing
	 * two reads. */
	Modes.data_len = MODES_DATA_LEN + (MODES_FULL_LEN - 1) * 4;
	Modes.data_ready = 0;
	/* Allocate the ICAO address cache. We use two uint32_t for every
	 * entry because it's a addr / timestamp pair for every entry. */
	Modes.icao_cache = malloc(sizeof(uint32_t)*MODES_ICAO_CACHE_LEN * 2);
	memset(Modes.icao_cache, 0, sizeof(uint32_t)*MODES_ICAO_CACHE_LEN * 2);
	Modes.aircrafts = NULL;
	Modes.interactive_last_update = 0;
	if ((Modes.data = malloc(Modes.data_len)) == NULL ||
			(Modes.magnitude = malloc(Modes.data_len * 2)) == NULL) {
		fprintf(stderr, "Out of memory allocating data buffer.\n");
		exit(1);
	}
	memset(Modes.data, 127, Modes.data_len);

	/* Populate the I/Q -> Magnitude lookup table. It is used because
	 * sqrt or round may be expensive and may vary a lot depending on
	 * the libc used.
	 *
	 * We scale to 0-255 range multiplying by 1.4 in order to ensure that
	 * every different I/Q pair will result in a different magnitude value,
	 * not losing any resolution. */
	Modes.maglut = malloc(129 * 129 * 2);
	for (i = 0; i <= 128; i++) {
		for (q = 0; q <= 128; q++) {
			Modes.maglut[i * 129 + q] = round(sqrt(i*i + q*q) * 360);
		}
	}

	/* Statistics */
	Modes.stat_valid_preamble = 0;
	Modes.stat_demodulated = 0;
	Modes.stat_goodcrc = 0;
	Modes.stat_badcrc = 0;
	Modes.stat_fixed = 0;
	Modes.stat_single_bit_fix = 0;
	Modes.stat_two_bits_fix = 0;
	Modes.stat_http_requests = 0;
	Modes.stat_sbs_connections = 0;
	Modes.stat_out_of_phase = 0;
	Modes.exit = 0;
}

/* =============================== PlutoSDR handling ========================== */

void modesInitPLUTOSDR(void) {
	int device_count;

	printf("* Acquiring IIO context\n");
	Modes.ctx = iio_create_default_context();
	if(Modes.ctx == NULL){
		Modes.ctx = iio_create_network_context("pluto.local");
	}
	device_count = iio_context_get_devices_count(Modes.ctx);
	if (!device_count) {
		fprintf(stderr, "No supported PLUTOSDR devices found.\n");
		exit(1);
	}

	fprintf(stderr, "Found %d device(s):\n", device_count);

	printf("* Acquiring AD9361 streaming devices\n");

	Modes.dev = iio_context_find_device(Modes.ctx, "cf-ad9361-lpc");

	if (Modes.dev == NULL) {
		fprintf(stderr, "Error opening the PLUTOSDR device: %s\n",
				strerror(errno));
		exit(1);
	}

	printf("* Acquiring AD9361 phy channel 0\n");

	struct iio_channel* phy_chn = iio_device_find_channel(iio_context_find_device(Modes.ctx, "ad9361-phy"), "voltage0", false);

	iio_channel_attr_write(phy_chn, "rf_port_select", "A_BALANCED");
	iio_channel_attr_write_longlong(phy_chn, "rf_bandwidth", MODES_DEFAULT_RATE);
	iio_channel_attr_write_longlong(phy_chn, "sampling_frequency", MODES_DEFAULT_RATE);

	struct iio_channel* lo_chn = iio_device_find_channel(iio_context_find_device(Modes.ctx, "ad9361-phy"), "altvoltage0", true);
	iio_channel_attr_write_longlong(lo_chn, "frequency", Modes.freq);

	printf("* Initializing AD9361 IIO streaming channels\n");

	Modes.rx0_i = iio_device_find_channel(Modes.dev, "voltage0", false);
	if (!Modes.rx0_i)
		Modes.rx0_i= iio_device_find_channel(Modes.dev, "altvoltage0", false);

	Modes.rx0_q = iio_device_find_channel(Modes.dev, "voltage1", false);
	if (!Modes.rx0_q)
		Modes.rx0_q = iio_device_find_channel(Modes.dev, "altvoltage1", false);

	ad9361_set_bb_rate(iio_context_find_device(Modes.ctx, "ad9361-phy"), MODES_DEFAULT_RATE);

	printf("* Enabling IIO streaming channels\n");

	iio_channel_enable(Modes.rx0_i);
	iio_channel_enable(Modes.rx0_q);

	printf("* Creating non-cyclic IIO buffers \n");

	Modes.rxbuf=iio_device_create_buffer(Modes.dev, MODES_DATA_LEN/2, false);

	if (!Modes.rxbuf) {
		perror("Could not create RX buffer");
	}

	if(Modes.gain==MODES_AUTO_GAIN){
		iio_channel_attr_write(phy_chn,"gain_control_mode","slow_attack");
	}else{
		if(Modes.gain>MODES_MAX_GAIN)
			Modes.gain=MODES_MAX_GAIN;
		iio_channel_attr_write(phy_chn,"gain_control_mode","manual");
		iio_channel_attr_write_longlong(phy_chn, "hardwaregain", Modes.gain);
	}


}

/* We use a thread reading data in background, while the main thread
 * handles decoding and visualization of data to the user.
 *
 * The reading thread calls the RTLSDR API to read data asynchronously, and
 * uses a callback to populate the data buffer.
 * A Mutex is used to avoid races with the decoding thread. */
void plutosdrCallback(unsigned char *buf, uint32_t len){
	pthread_mutex_lock(&Modes.data_mutex);
	uint32_t i;
	for (i = 0; i < len; i++){
		buf[i]^= (uint8_t)0x80;
	}
	if (len > MODES_DATA_LEN) len = MODES_DATA_LEN;
	/* Move the last part of the previous buffer, that was not processed,
	 * on the start of the new buffer. */
	memcpy(Modes.data, Modes.data+MODES_DATA_LEN, (MODES_FULL_LEN-1)*4);
	/* Read the new data. */
	memcpy(Modes.data+(MODES_FULL_LEN-1)*4, buf, len);
	Modes.data_ready = 1;
	/* Signal to the other thread that new data is ready */
	pthread_cond_signal(&Modes.data_cond);
	pthread_mutex_unlock(&Modes.data_mutex);

}
/* This is used when --ifile is specified in order to read data from file
 * instead of using an RTLSDR device. */
void readDataFromFile(void) {
	pthread_mutex_lock(&Modes.data_mutex);
	while (1) {
		ssize_t nread, toread;
		unsigned char *p;

		if (Modes.data_ready) {
			pthread_cond_wait(&Modes.data_cond, &Modes.data_mutex);
			continue;
		}

		if (Modes.interactive) {
			/* When --ifile and --interactive are used together, slow down
			 * playing at the natural rate of the RTLSDR received. */
			pthread_mutex_unlock(&Modes.data_mutex);
			usleep(5000);
			pthread_mutex_lock(&Modes.data_mutex);
		}

		/* Move the last part of the previous buffer, that was not processed,
		 * on the start of the new buffer. */
		memcpy(Modes.data, Modes.data + MODES_DATA_LEN, (MODES_FULL_LEN - 1) * 4);
		toread = MODES_DATA_LEN;
		p = Modes.data + (MODES_FULL_LEN - 1) * 4;
		while (toread) {
			nread = read(Modes.fd, p, toread);
			if (nread <= 0) {
				Modes.exit = 1; /* Signal the other thread to exit. */
				break;
			}
			p += nread;
			toread -= nread;
		}
		if (toread) {
			/* Not enough data on file to fill the buffer? Pad with
			 * no signal. */
			memset(p, 127, toread);
		}
		Modes.data_ready = 1;
		/* Signal to the other thread that new data is ready */
		pthread_cond_signal(&Modes.data_cond);
	}
}

/* We read data using a thread, so the main thread only handles decoding
 * without caring about data acquisition. */
void *readerThreadEntryPoint(void *arg) {

	MODES_NOTUSED(arg);

	if (Modes.filename == NULL) {
		unsigned char cb_buf[MODES_DATA_LEN];

		while(!Modes.stop){
			void *p_dat, *p_end;
			ptrdiff_t p_inc;
			int j=0;
			iio_buffer_refill(Modes.rxbuf);
			p_inc = iio_buffer_step(Modes.rxbuf);
			p_end = iio_buffer_end(Modes.rxbuf);
			p_dat = iio_buffer_first(Modes.rxbuf, Modes.rx0_i);
			for(p_dat = iio_buffer_first(Modes.rxbuf, Modes.rx0_i);p_dat < p_end; p_dat += p_inc){
				const int16_t i = ((int16_t*)p_dat)[0]; // Real (I)
				const int16_t q = ((int16_t*)p_dat)[1]; // Imag (Q)
				cb_buf[j*2]=i>>4;
				cb_buf[j*2+1]=q>>4;
				j++;

			}
			plutosdrCallback(cb_buf,MODES_DATA_LEN);	
		}


	}
	else {
		readDataFromFile();
	}
	return NULL;
}

/* ============================== Debugging ================================= */

/* Helper function for dumpMagnitudeVector().
 * It prints a single bar used to display raw signals.
 *
 * Since every magnitude sample is between 0-255, the function uses
 * up to 63 characters for every bar. Every character represents
 * a length of 4, 3, 2, 1, specifically:
 *
 * "O" is 4
 * "o" is 3
 * "-" is 2
 * "." is 1
 */
void dumpMagnitudeBar(int index, int magnitude) {
	char *set = " .-o";
	char buf[256];
	int div = magnitude / 256 / 4;
	int rem = magnitude / 256 % 4;

	memset(buf, 'O', div);
	buf[div] = set[rem];
	buf[div + 1] = '\0';

	if (index >= 0)
		printf("[%.3d] |%-66s %d\n", index, buf, magnitude);
	else
		printf("[%.2d] |%-66s %d\n", index, buf, magnitude);
}

/* Display an ASCII-art alike graphical representation of the undecoded
 * message as a magnitude signal.
 *
 * The message starts at the specified offset in the "m" buffer.
 * The function will display enough data to cover a short 56 bit message.
 *
 * If possible a few samples before the start of the messsage are included
 * for context. */

void dumpMagnitudeVector(uint16_t *m, uint32_t offset) {
	uint32_t padding = 5; /* Show a few samples before the actual start. */
	uint32_t start = (offset < padding) ? 0 : offset - padding;
	uint32_t end = offset + (MODES_PREAMBLE_US * 2) + (MODES_SHORT_MSG_BITS * 2) - 1;
	uint32_t j;

	for (j = start; j <= end; j++) {
		dumpMagnitudeBar(j - offset, m[j]);
	}
}

/* Produce a raw representation of the message as a Javascript file
 * loadable by debug.html. */
void dumpRawMessageJS(char *descr, unsigned char *msg,
		uint16_t *m, uint32_t offset, int fixable)
{
	int padding = 5; /* Show a few samples before the actual start. */
	int start = offset - padding;
	int end = offset + (MODES_PREAMBLE_US * 2) + (MODES_LONG_MSG_BITS * 2) - 1;
	FILE *fp;
	int j, fix1 = -1, fix2 = -1;

	if (fixable != -1) {
		fix1 = fixable & 0xff;
		if (fixable > 255) fix2 = fixable >> 8;
	}

	if ((fp = fopen("frames.js", "a")) == NULL) {
		fprintf(stderr, "Error opening frames.js: %s\n", strerror(errno));
		exit(1);
	}

	fprintf(fp, "frames.push({\"descr\": \"%s\", \"mag\": [", descr);
	for (j = start; j <= end; j++) {
		fprintf(fp, "%d", j < 0 ? 0 : m[j]);
		if (j != end) fprintf(fp, ",");
	}
	fprintf(fp, "], \"fix1\": %d, \"fix2\": %d, \"bits\": %d, \"hex\": \"",
			fix1, fix2, modesMessageLenByType(msg[0] >> 3));
	for (j = 0; j < MODES_LONG_MSG_BYTES; j++)
		fprintf(fp, "\\x%02x", msg[j]);
	fprintf(fp, "\"});\n");
	fclose(fp);
}

/* This is a wrapper for dumpMagnitudeVector() that also show the message
 * in hex format with an additional description.
 *
 * descr  is the additional message to show to describe the dump.
 * msg    points to the decoded message
 * m      is the original magnitude vector
 * offset is the offset where the message starts
 *
 * The function also produces the Javascript file used by debug.html to
 * display packets in a graphical format if the Javascript output was
 * enabled.
 */
void dumpRawMessage(char *descr, unsigned char *msg,
		uint16_t *m, uint32_t offset)
{
	int j;
	int msgtype = msg[0] >> 3;
	int fixable = -1;

	if (msgtype == 11 || msgtype == 17) {
		int msgbits = (msgtype == 11) ? MODES_SHORT_MSG_BITS :
			MODES_LONG_MSG_BITS;
		fixable = fixSingleBitErrors(msg, msgbits);
		if (fixable == -1)
			fixable = fixTwoBitsErrors(msg, msgbits);
	}

	if (Modes.debug & MODES_DEBUG_JS) {
		dumpRawMessageJS(descr, msg, m, offset, fixable);
		return;
	}

	printf("\n--- %s\n    ", descr);
	for (j = 0; j < MODES_LONG_MSG_BYTES; j++) {
		printf("%02x", msg[j]);
		if (j == MODES_SHORT_MSG_BYTES - 1) printf(" ... ");
	}
	printf(" (DF %d, Fixable: %d)\n", msgtype, fixable);
	dumpMagnitudeVector(m, offset);
	printf("---\n\n");
}

/* ===================== Mode S detection and decoding  ===================== */

/* Parity table for MODE S Messages.
 * The table contains 112 elements, every element corresponds to a bit set
 * in the message, starting from the first bit of actual data after the
 * preamble.
 *
 * For messages of 112 bit, the whole table is used.
 * For messages of 56 bits only the last 56 elements are used.
 *
 * The algorithm is as simple as xoring all the elements in this table
 * for which the corresponding bit on the message is set to 1.
 *
 * The latest 24 elements in this table are set to 0 as the checksum at the
 * end of the message should not affect the computation.
 *
 * Note: this function can be used with DF11 and DF17, other modes have
 * the CRC xored with the sender address as they are reply to interrogations,
 * but a casual listener can't split the address from the checksum.
 */
uint32_t modes_checksum_table[112] = {
	0x3935ea, 0x1c9af5, 0xf1b77e, 0x78dbbf, 0xc397db, 0x9e31e9, 0xb0e2f0, 0x587178,
	0x2c38bc, 0x161c5e, 0x0b0e2f, 0xfa7d13, 0x82c48d, 0xbe9842, 0x5f4c21, 0xd05c14,
	0x682e0a, 0x341705, 0xe5f186, 0x72f8c3, 0xc68665, 0x9cb936, 0x4e5c9b, 0xd8d449,
	0x939020, 0x49c810, 0x24e408, 0x127204, 0x093902, 0x049c81, 0xfdb444, 0x7eda22,
	0x3f6d11, 0xe04c8c, 0x702646, 0x381323, 0xe3f395, 0x8e03ce, 0x4701e7, 0xdc7af7,
	0x91c77f, 0xb719bb, 0xa476d9, 0xadc168, 0x56e0b4, 0x2b705a, 0x15b82d, 0xf52612,
	0x7a9309, 0xc2b380, 0x6159c0, 0x30ace0, 0x185670, 0x0c2b38, 0x06159c, 0x030ace,
	0x018567, 0xff38b7, 0x80665f, 0xbfc92b, 0xa01e91, 0xaff54c, 0x57faa6, 0x2bfd53,
	0xea04ad, 0x8af852, 0x457c29, 0xdd4410, 0x6ea208, 0x375104, 0x1ba882, 0x0dd441,
	0xf91024, 0x7c8812, 0x3e4409, 0xe0d800, 0x706c00, 0x383600, 0x1c1b00, 0x0e0d80,
	0x0706c0, 0x038360, 0x01c1b0, 0x00e0d8, 0x00706c, 0x003836, 0x001c1b, 0xfff409,
	0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000,
	0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000,
	0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000
};

uint32_t modesChecksum(unsigned char *msg, int bits) {
	uint32_t crc = 0;
	int offset = (bits == 112) ? 0 : (112 - 56);
	int j;

	for (j = 0; j < bits; j++) {
		int byte = j / 8;
		int bit = j % 8;
		int bitmask = 1 << (7 - bit);

		/* If bit is set, xor with corresponding table entry. */
		if (msg[byte] & bitmask)
			crc ^= modes_checksum_table[j + offset];
	}
	return crc; /* 24 bit checksum. */
}

/* Given the Downlink Format (DF) of the message, return the message length
 * in bits. */
int modesMessageLenByType(int type) {
	if (type == 16 || type == 17 ||
			type == 19 || type == 20 ||
			type == 21)
		return MODES_LONG_MSG_BITS;
	else
		return MODES_SHORT_MSG_BITS;
}

/* Try to fix single bit errors using the checksum. On success modifies
 * the original buffer with the fixed version, and returns the position
 * of the error bit. Otherwise if fixing failed -1 is returned. */
int fixSingleBitErrors(unsigned char *msg, int bits) {
	int j;
	unsigned char aux[MODES_LONG_MSG_BITS / 8];

	for (j = 0; j < bits; j++) {
		int byte = j / 8;
		int bitmask = 1 << (7 - (j % 8));
		uint32_t crc1, crc2;

		memcpy(aux, msg, bits / 8);
		aux[byte] ^= bitmask; /* Flip j-th bit. */

		crc1 = ((uint32_t)aux[(bits / 8) - 3] << 16) |
			((uint32_t)aux[(bits / 8) - 2] << 8) |
			(uint32_t)aux[(bits / 8) - 1];
		crc2 = modesChecksum(aux, bits);

		if (crc1 == crc2) {
			/* The error is fixed. Overwrite the original buffer with
			 * the corrected sequence, and returns the error bit
			 * position. */
			memcpy(msg, aux, bits / 8);
			return j;
		}
	}
	return -1;
}

/* Similar to fixSingleBitErrors() but try every possible two bit combination.
 * This is very slow and should be tried only against DF17 messages that
 * don't pass the checksum, and only in Aggressive Mode. */
int fixTwoBitsErrors(unsigned char *msg, int bits) {
	int j, i;
	unsigned char aux[MODES_LONG_MSG_BITS / 8];

	for (j = 0; j < bits; j++) {
		int byte1 = j / 8;
		int bitmask1 = 1 << (7 - (j % 8));

		/* Don't check the same pairs multiple times, so i starts from j+1 */
		for (i = j + 1; i < bits; i++) {
			int byte2 = i / 8;
			int bitmask2 = 1 << (7 - (i % 8));
			uint32_t crc1, crc2;

			memcpy(aux, msg, bits / 8);

			aux[byte1] ^= bitmask1; /* Flip j-th bit. */
			aux[byte2] ^= bitmask2; /* Flip i-th bit. */

			crc1 = ((uint32_t)aux[(bits / 8) - 3] << 16) |
				((uint32_t)aux[(bits / 8) - 2] << 8) |
				(uint32_t)aux[(bits / 8) - 1];
			crc2 = modesChecksum(aux, bits);

			if (crc1 == crc2) {
				/* The error is fixed. Overwrite the original buffer with
				 * the corrected sequence, and returns the error bit
				 * position. */
				memcpy(msg, aux, bits / 8);
				/* We return the two bits as a 16 bit integer by shifting
				 * 'i' on the left. This is possible since 'i' will always
				 * be non-zero because i starts from j+1. */
				return j | (i << 8);
			}
		}
	}
	return -1;
}

/* Hash the ICAO address to index our cache of MODES_ICAO_CACHE_LEN
 * elements, that is assumed to be a power of two. */
uint32_t ICAOCacheHashAddress(uint32_t a) {
	/* The following three rounds wil make sure that every bit affects
	 * every output bit with ~ 50% of probability. */
	a = ((a >> 16) ^ a) * 0x45d9f3b;
	a = ((a >> 16) ^ a) * 0x45d9f3b;
	a = ((a >> 16) ^ a);
	return a & (MODES_ICAO_CACHE_LEN - 1);
}

/* Add the specified entry to the cache of recently seen ICAO addresses.
 * Note that we also add a timestamp so that we can make sure that the
 * entry is only valid for MODES_ICAO_CACHE_TTL seconds. */
void addRecentlySeenICAOAddr(uint32_t addr) {
	uint32_t h = ICAOCacheHashAddress(addr);
	Modes.icao_cache[h * 2] = addr;
	Modes.icao_cache[h * 2 + 1] = (uint32_t)time(NULL);
}

/* Returns 1 if the specified ICAO address was seen in a DF format with
 * proper checksum (not xored with address) no more than * MODES_ICAO_CACHE_TTL
 * seconds ago. Otherwise returns 0. */
int ICAOAddressWasRecentlySeen(uint32_t addr) {
	uint32_t h = ICAOCacheHashAddress(addr);
	uint32_t a = Modes.icao_cache[h * 2];
	uint32_t t = Modes.icao_cache[h * 2 + 1];

	return a && a == addr && time(NULL) - t <= MODES_ICAO_CACHE_TTL;
}

/* If the message type has the checksum xored with the ICAO address, try to
 * brute force it using a list of recently seen ICAO addresses.
 *
 * Do this in a brute-force fashion by xoring the predicted CRC with
 * the address XOR checksum field in the message. This will recover the
 * address: if we found it in our cache, we can assume the message is ok.
 *
 * This function expects mm->msgtype and mm->msgbits to be correctly
 * populated by the caller.
 *
 * On success the correct ICAO address is stored in the modesMessage
 * structure in the aa3, aa2, and aa1 fiedls.
 *
 * If the function successfully recovers a message with a correct checksum
 * it returns 1. Otherwise 0 is returned. */
int bruteForceAP(unsigned char *msg, struct modesMessage *mm) {
	unsigned char aux[MODES_LONG_MSG_BYTES];
	int msgtype = mm->msgtype;
	int msgbits = mm->msgbits;

	if (msgtype == 0 ||         /* Short air surveillance */
			msgtype == 4 ||         /* Surveillance, altitude reply */
			msgtype == 5 ||         /* Surveillance, identity reply */
			msgtype == 16 ||        /* Long Air-Air survillance */
			msgtype == 20 ||        /* Comm-A, altitude request */
			msgtype == 21 ||        /* Comm-A, identity request */
			msgtype == 24)          /* Comm-C ELM */
	{
		uint32_t addr;
		uint32_t crc;
		int lastbyte = (msgbits / 8) - 1;

		/* Work on a copy. */
		memcpy(aux, msg, msgbits / 8);

		/* Compute the CRC of the message and XOR it with the AP field
		 * so that we recover the address, because:
		 *
		 * (ADDR xor CRC) xor CRC = ADDR. */
		crc = modesChecksum(aux, msgbits);
		aux[lastbyte] ^= crc & 0xff;
		aux[lastbyte - 1] ^= (crc >> 8) & 0xff;
		aux[lastbyte - 2] ^= (crc >> 16) & 0xff;

		/* If the obtained address exists in our cache we consider
		 * the message valid. */
		addr = aux[lastbyte] | (aux[lastbyte - 1] << 8) | (aux[lastbyte - 2] << 16);
		if (ICAOAddressWasRecentlySeen(addr)) {
			mm->aa1 = aux[lastbyte - 2];
			mm->aa2 = aux[lastbyte - 1];
			mm->aa3 = aux[lastbyte];
			return 1;
		}
	}
	return 0;
}

/* Decode the 13 bit AC altitude field (in DF 20 and others).
 * Returns the altitude, and set 'unit' to either MODES_UNIT_METERS
 * or MDOES_UNIT_FEETS. */
int decodeAC13Field(unsigned char *msg, int *unit) {
	int m_bit = msg[3] & (1 << 6);
	int q_bit = msg[3] & (1 << 4);

	if (!m_bit) {
		*unit = MODES_UNIT_FEET;
		if (q_bit) {
			/* N is the 11 bit integer resulting from the removal of bit
			 * Q and M */
			int n = ((msg[2] & 31) << 6) |
				((msg[3] & 0x80) >> 2) |
				((msg[3] & 0x20) >> 1) |
				(msg[3] & 15);
			/* The final altitude is due to the resulting number multiplied
			 * by 25, minus 1000. */
			return n * 25 - 1000;
		}
		else {
			/* TODO: Implement altitude where Q=0 and M=0 */
		}
	}
	else {
		*unit = MODES_UNIT_METERS;
		/* TODO: Implement altitude when meter unit is selected. */
	}
	return 0;
}

/* Decode the 12 bit AC altitude field (in DF 17 and others).
 * Returns the altitude or 0 if it can't be decoded. */
int decodeAC12Field(unsigned char *msg, int *unit) {
	int q_bit = msg[5] & 1;

	if (q_bit) {
		/* N is the 11 bit integer resulting from the removal of bit
		 * Q */
		*unit = MODES_UNIT_FEET;
		int n = ((msg[5] >> 1) << 4) | ((msg[6] & 0xF0) >> 4);
		/* The final altitude is due to the resulting number multiplied
		 * by 25, minus 1000. */
		return n * 25 - 1000;
	}
	else {
		return 0;
	}
}

/* Capability table. */
char *ca_str[8] = {
	/* 0 */ "Level 1 (Survillance Only)",
	/* 1 */ "Level 2 (DF0,4,5,11)",
	/* 2 */ "Level 3 (DF0,4,5,11,20,21)",
	/* 3 */ "Level 4 (DF0,4,5,11,20,21,24)",
	/* 4 */ "Level 2+3+4 (DF0,4,5,11,20,21,24,code7 - is on ground)",
	/* 5 */ "Level 2+3+4 (DF0,4,5,11,20,21,24,code7 - is on airborne)",
	/* 6 */ "Level 2+3+4 (DF0,4,5,11,20,21,24,code7)",
	/* 7 */ "Level 7 ???"
};

/* Flight status table. */
char *fs_str[8] = {
	/* 0 */ "Normal, Airborne",
	/* 1 */ "Normal, On the ground",
	/* 2 */ "ALERT,  Airborne",
	/* 3 */ "ALERT,  On the ground",
	/* 4 */ "ALERT & Special Position Identification. Airborne or Ground",
	/* 5 */ "Special Position Identification. Airborne or Ground",
	/* 6 */ "Value 6 is not assigned",
	/* 7 */ "Value 7 is not assigned"
};

/* ME message type to description table. */
char *me_str[] = {
};

char *getMEDescription(int metype, int mesub) {
	char *mename = "Unknown";

	if (metype >= 1 && metype <= 4)
		mename = "Aircraft Identification and Category";
	else if (metype >= 5 && metype <= 8)
		mename = "Surface Position";
	else if (metype >= 9 && metype <= 18)
		mename = "Airborne Position (Baro Altitude)";
	else if (metype == 19 && mesub >= 1 && mesub <= 4)
		mename = "Airborne Velocity";
	else if (metype >= 20 && metype <= 22)
		mename = "Airborne Position (GNSS Height)";
	else if (metype == 23 && mesub == 0)
		mename = "Test Message";
	else if (metype == 24 && mesub == 1)
		mename = "Surface System Status";
	else if (metype == 28 && mesub == 1)
		mename = "Extended Squitter Aircraft Status (Emergency)";
	else if (metype == 28 && mesub == 2)
		mename = "Extended Squitter Aircraft Status (1090ES TCAS RA)";
	else if (metype == 29 && (mesub == 0 || mesub == 1))
		mename = "Target State and Status Message";
	else if (metype == 31 && (mesub == 0 || mesub == 1))
		mename = "Aircraft Operational Status Message";
	return mename;
}

/* Decode a raw Mode S message demodulated as a stream of bytes by
 * detectModeS(), and split it into fields populating a modesMessage
 * structure. */
void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
	uint32_t crc2;   /* Computed CRC, used to verify the message CRC. */
	char *ais_charset = "?ABCDEFGHIJKLMNOPQRSTUVWXYZ????? ???????????????0123456789??????";

	/* Work on our local copy */
	memcpy(mm->msg, msg, MODES_LONG_MSG_BYTES);
	msg = mm->msg;

	/* Get the message type ASAP as other operations depend on this */
	mm->msgtype = msg[0] >> 3;    /* Downlink Format */
	mm->msgbits = modesMessageLenByType(mm->msgtype);

	/* CRC is always the last three bytes. */
	mm->crc = ((uint32_t)msg[(mm->msgbits / 8) - 3] << 16) |
		((uint32_t)msg[(mm->msgbits / 8) - 2] << 8) |
		(uint32_t)msg[(mm->msgbits / 8) - 1];
	crc2 = modesChecksum(msg, mm->msgbits);

	/* Check CRC and fix single bit errors using the CRC when
	 * possible (DF 11 and 17). */
	mm->errorbit = -1;  /* No error */
	mm->crcok = (mm->crc == crc2);

	if (!mm->crcok && Modes.fix_errors &&
			(mm->msgtype == 11 || mm->msgtype == 17))
	{
		if ((mm->errorbit = fixSingleBitErrors(msg, mm->msgbits)) != -1) {
			mm->crc = modesChecksum(msg, mm->msgbits);
			mm->crcok = 1;
		}
		else if (Modes.aggressive && mm->msgtype == 17 &&
				(mm->errorbit = fixTwoBitsErrors(msg, mm->msgbits)) != -1)
		{
			mm->crc = modesChecksum(msg, mm->msgbits);
			mm->crcok = 1;
		}
	}

	/* Note that most of the other computation happens *after* we fix
	 * the single bit errors, otherwise we would need to recompute the
	 * fields again. */
	mm->ca = msg[0] & 7;        /* Responder capabilities. */

	/* ICAO address */
	mm->aa1 = msg[1];
	mm->aa2 = msg[2];
	mm->aa3 = msg[3];

	/* DF 17 type (assuming this is a DF17, otherwise not used) */
	mm->metype = msg[4] >> 3;   /* Extended squitter message type. */
	mm->mesub = msg[4] & 7;     /* Extended squitter message subtype. */

	/* Fields for DF4,5,20,21 */
	mm->fs = msg[0] & 7;        /* Flight status for DF4,5,20,21 */
	mm->dr = msg[1] >> 3 & 31;  /* Request extraction of downlink request. */
	mm->um = ((msg[1] & 7) << 3) | /* Request extraction of downlink request. */
		msg[2] >> 5;

	/* In the squawk (identity) field bits are interleaved like that
	 * (message bit 20 to bit 32):
	 *
	 * C1-A1-C2-A2-C4-A4-ZERO-B1-D1-B2-D2-B4-D4
	 *
	 * So every group of three bits A, B, C, D represent an integer
	 * from 0 to 7.
	 *
	 * The actual meaning is just 4 octal numbers, but we convert it
	 * into a base ten number tha happens to represent the four
	 * octal numbers.
	 *
	 * For more info: http://en.wikipedia.org/wiki/Gillham_code */
	{
		int a, b, c, d;

		a = ((msg[3] & 0x80) >> 5) |
			((msg[2] & 0x02) >> 0) |
			((msg[2] & 0x08) >> 3);
		b = ((msg[3] & 0x02) << 1) |
			((msg[3] & 0x08) >> 2) |
			((msg[3] & 0x20) >> 5);
		c = ((msg[2] & 0x01) << 2) |
			((msg[2] & 0x04) >> 1) |
			((msg[2] & 0x10) >> 4);
		d = ((msg[3] & 0x01) << 2) |
			((msg[3] & 0x04) >> 1) |
			((msg[3] & 0x10) >> 4);
		mm->identity = a * 1000 + b * 100 + c * 10 + d;
	}

	/* DF 11 & 17: try to populate our ICAO addresses whitelist.
	 * DFs with an AP field (xored addr and crc), try to decode it. */
	if (mm->msgtype != 11 && mm->msgtype != 17) {
		/* Check if we can check the checksum for the Downlink Formats where
		 * the checksum is xored with the aircraft ICAO address. We try to
		 * brute force it using a list of recently seen aircraft addresses. */
		if (bruteForceAP(msg, mm)) {
			/* We recovered the message, mark the checksum as valid. */
			mm->crcok = 1;
		}
		else {
			mm->crcok = 0;
		}
	}
	else {
		/* If this is DF 11 or DF 17 and the checksum was ok,
		 * we can add this address to the list of recently seen
		 * addresses. */
		if (mm->crcok && mm->errorbit == -1) {
			uint32_t addr = (mm->aa1 << 16) | (mm->aa2 << 8) | mm->aa3;
			addRecentlySeenICAOAddr(addr);
		}
	}

	/* Decode 13 bit altitude for DF0, DF4, DF16, DF20 */
	if (mm->msgtype == 0 || mm->msgtype == 4 ||
			mm->msgtype == 16 || mm->msgtype == 20) {
		mm->altitude = decodeAC13Field(msg, &mm->unit);
	}

	/* Decode extended squitter specific stuff. */
	if (mm->msgtype == 17) {
		/* Decode the extended squitter message. */

		if (mm->metype >= 1 && mm->metype <= 4) {
			/* Aircraft Identification and Category */
			mm->aircraft_type = mm->metype - 1;
			mm->flight[0] = ais_charset[msg[5] >> 2];
			mm->flight[1] = ais_charset[((msg[5] & 3) << 4) | (msg[6] >> 4)];
			mm->flight[2] = ais_charset[((msg[6] & 15) << 2) | (msg[7] >> 6)];
			mm->flight[3] = ais_charset[msg[7] & 63];
			mm->flight[4] = ais_charset[msg[8] >> 2];
			mm->flight[5] = ais_charset[((msg[8] & 3) << 4) | (msg[9] >> 4)];
			mm->flight[6] = ais_charset[((msg[9] & 15) << 2) | (msg[10] >> 6)];
			mm->flight[7] = ais_charset[msg[10] & 63];
			mm->flight[8] = '\0';
		}
		else if (mm->metype >= 9 && mm->metype <= 18) {
			/* Airborne position Message */
			mm->fflag = msg[6] & (1 << 2);
			mm->tflag = msg[6] & (1 << 3);
			mm->altitude = decodeAC12Field(msg, &mm->unit);
			mm->raw_latitude = ((msg[6] & 3) << 15) |
				(msg[7] << 7) |
				(msg[8] >> 1);
			mm->raw_longitude = ((msg[8] & 1) << 16) |
				(msg[9] << 8) |
				msg[10];
		}
		else if (mm->metype == 19 && mm->mesub >= 1 && mm->mesub <= 4) {
			/* Airborne Velocity Message */
			if (mm->mesub == 1 || mm->mesub == 2) {
				mm->ew_dir = (msg[5] & 4) >> 2;
				mm->ew_velocity = ((msg[5] & 3) << 8) | msg[6];
				mm->ns_dir = (msg[7] & 0x80) >> 7;
				mm->ns_velocity = ((msg[7] & 0x7f) << 3) | ((msg[8] & 0xe0) >> 5);
				mm->vert_rate_source = (msg[8] & 0x10) >> 4;
				mm->vert_rate_sign = (msg[8] & 0x8) >> 3;
				mm->vert_rate = ((msg[8] & 7) << 6) | ((msg[9] & 0xfc) >> 2);
				/* Compute velocity and angle from the two speed
				 * components. */
				mm->velocity = sqrt(mm->ns_velocity*mm->ns_velocity +
						mm->ew_velocity*mm->ew_velocity);
				if (mm->velocity) {
					int ewv = mm->ew_velocity;
					int nsv = mm->ns_velocity;
					double heading;

					if (mm->ew_dir) ewv *= -1;
					if (mm->ns_dir) nsv *= -1;
					heading = atan2(ewv, nsv);

					/* Convert to degrees. */
					mm->heading = heading * 360 / (M_PI * 2);
					/* We don't want negative values but a 0-360 scale. */
					if (mm->heading < 0) mm->heading += 360;
				}
				else {
					mm->heading = 0;
				}
			}
			else if (mm->mesub == 3 || mm->mesub == 4) {
				mm->heading_is_valid = msg[5] & (1 << 2);
				mm->heading = (360.0 / 128) * (((msg[5] & 3) << 5) |
						(msg[6] >> 3));
			}
		}
	}
	mm->phase_corrected = 0; /* Set to 1 by the caller if needed. */
}

/* This function gets a decoded Mode S Message and prints it on the screen
 * in a human readable format. */
void displayModesMessage(struct modesMessage *mm) {
	int j;

	/* Handle only addresses mode first. */
	if (Modes.onlyaddr) {
		printf("%02x%02x%02x\n", mm->aa1, mm->aa2, mm->aa3);
		return;
	}

	/* Show the raw message. */
	printf("*");
	for (j = 0; j < mm->msgbits / 8; j++) printf("%02x", mm->msg[j]);
	printf(";\n");

	if (Modes.raw) {
		fflush(stdout); /* Provide data to the reader ASAP. */
		return; /* Enough for --raw mode */
	}

	printf("CRC: %06x (%s)\n", (int)mm->crc, mm->crcok ? "ok" : "wrong");
	if (mm->errorbit != -1)
		printf("Single bit error fixed, bit %d\n", mm->errorbit);

	if (mm->msgtype == 0) {
		/* DF 0 */
		printf("DF 0: Short Air-Air Surveillance.\n");
		printf("  Altitude       : %d %s\n", mm->altitude,
				(mm->unit == MODES_UNIT_METERS) ? "meters" : "feet");
		printf("  ICAO Address   : %02x%02x%02x\n", mm->aa1, mm->aa2, mm->aa3);
	}
	else if (mm->msgtype == 4 || mm->msgtype == 20) {
		printf("DF %d: %s, Altitude Reply.\n", mm->msgtype,
				(mm->msgtype == 4) ? "Surveillance" : "Comm-B");
		printf("  Flight Status  : %s\n", fs_str[mm->fs]);
		printf("  DR             : %d\n", mm->dr);
		printf("  UM             : %d\n", mm->um);
		printf("  Altitude       : %d %s\n", mm->altitude,
				(mm->unit == MODES_UNIT_METERS) ? "meters" : "feet");
		printf("  ICAO Address   : %02x%02x%02x\n", mm->aa1, mm->aa2, mm->aa3);

		if (mm->msgtype == 20) {
			/* TODO: 56 bits DF20 MB additional field. */
		}
	}
	else if (mm->msgtype == 5 || mm->msgtype == 21) {
		printf("DF %d: %s, Identity Reply.\n", mm->msgtype,
				(mm->msgtype == 5) ? "Surveillance" : "Comm-B");
		printf("  Flight Status  : %s\n", fs_str[mm->fs]);
		printf("  DR             : %d\n", mm->dr);
		printf("  UM             : %d\n", mm->um);
		printf("  Squawk         : %d\n", mm->identity);
		printf("  ICAO Address   : %02x%02x%02x\n", mm->aa1, mm->aa2, mm->aa3);

		if (mm->msgtype == 21) {
			/* TODO: 56 bits DF21 MB additional field. */
		}
	}
	else if (mm->msgtype == 11) {
		/* DF 11 */
		printf("DF 11: All Call Reply.\n");
		printf("  Capability  : %s\n", ca_str[mm->ca]);
		printf("  ICAO Address: %02x%02x%02x\n", mm->aa1, mm->aa2, mm->aa3);
	}
	else if (mm->msgtype == 17) {
		/* DF 17 */
		printf("DF 17: ADS-B message.\n");
		printf("  Capability     : %d (%s)\n", mm->ca, ca_str[mm->ca]);
		printf("  ICAO Address   : %02x%02x%02x\n", mm->aa1, mm->aa2, mm->aa3);
		printf("  Extended Squitter  Type: %d\n", mm->metype);
		printf("  Extended Squitter  Sub : %d\n", mm->mesub);
		printf("  Extended Squitter  Name: %s\n",
				getMEDescription(mm->metype, mm->mesub));

		/* Decode the extended squitter message. */
		if (mm->metype >= 1 && mm->metype <= 4) {
			/* Aircraft identification. */
			char *ac_type_str[4] = {
				"Aircraft Type D",
				"Aircraft Type C",
				"Aircraft Type B",
				"Aircraft Type A"
			};

			printf("    Aircraft Type  : %s\n", ac_type_str[mm->aircraft_type]);
			printf("    Identification : %s\n", mm->flight);
		}
		else if (mm->metype >= 9 && mm->metype <= 18) {
			printf("    F flag   : %s\n", mm->fflag ? "odd" : "even");
			printf("    T flag   : %s\n", mm->tflag ? "UTC" : "non-UTC");
			printf("    Altitude : %d feet\n", mm->altitude);
			printf("    Latitude : %d (not decoded)\n", mm->raw_latitude);
			printf("    Longitude: %d (not decoded)\n", mm->raw_longitude);
		}
		else if (mm->metype == 19 && mm->mesub >= 1 && mm->mesub <= 4) {
			if (mm->mesub == 1 || mm->mesub == 2) {
				/* Velocity */
				printf("    EW direction      : %d\n", mm->ew_dir);
				printf("    EW velocity       : %d\n", mm->ew_velocity);
				printf("    NS direction      : %d\n", mm->ns_dir);
				printf("    NS velocity       : %d\n", mm->ns_velocity);
				printf("    Vertical rate src : %d\n", mm->vert_rate_source);
				printf("    Vertical rate sign: %d\n", mm->vert_rate_sign);
				printf("    Vertical rate     : %d\n", mm->vert_rate);
			}
			else if (mm->mesub == 3 || mm->mesub == 4) {
				printf("    Heading status: %d", mm->heading_is_valid);
				printf("    Heading: %d", mm->heading);
			}
		}
		else {
			printf("    Unrecognized ME type: %d subtype: %d\n",
					mm->metype, mm->mesub);
		}
	}
	else {
		if (Modes.check_crc)
			printf("DF %d with good CRC received "
					"(decoding still not implemented).\n",
					mm->msgtype);
	}
}

/* Turn I/Q samples pointed by Modes.data into the magnitude vector
 * pointed by Modes.magnitude. */
void computeMagnitudeVector(void) {
	uint16_t *m = Modes.magnitude;
	unsigned char *p = Modes.data;
	uint32_t j;

	/* Compute the magnitudo vector. It's just SQRT(I^2 + Q^2), but
	 * we rescale to the 0-255 range to exploit the full resolution. */
	for (j = 0; j < Modes.data_len; j += 2) {
		int i = p[j] - 127;
		int q = p[j + 1] - 127;

		if (i < 0) i = -i;
		if (q < 0) q = -q;
		m[j / 2] = Modes.maglut[i * 129 + q];
	}
}

/* Return -1 if the message is out of fase left-side
 * Return  1 if the message is out of fase right-size
 * Return  0 if the message is not particularly out of phase.
 *
 * Note: this function will access m[-1], so the caller should make sure to
 * call it only if we are not at the start of the current buffer. */
int detectOutOfPhase(uint16_t *m) {
	if (m[3] > m[2] / 3) return 1;
	if (m[10] > m[9] / 3) return 1;
	if (m[6] > m[7] / 3) return -1;
	if (m[-1] > m[1] / 3) return -1;
	return 0;
}

/* This function does not really correct the phase of the message, it just
 * applies a transformation to the first sample representing a given bit:
 *
 * If the previous bit was one, we amplify it a bit.
 * If the previous bit was zero, we decrease it a bit.
 *
 * This simple transformation makes the message a bit more likely to be
 * correctly decoded for out of phase messages:
 *
 * When messages are out of phase there is more uncertainty in
 * sequences of the same bit multiple times, since 11111 will be
 * transmitted as continuously altering magnitude (high, low, high, low...)
 *
 * However because the message is out of phase some part of the high
 * is mixed in the low part, so that it is hard to distinguish if it is
 * a zero or a one.
 *
 * However when the message is out of phase passing from 0 to 1 or from
 * 1 to 0 happens in a very recognizable way, for instance in the 0 -> 1
 * transition, magnitude goes low, high, high, low, and one of of the
 * two middle samples the high will be *very* high as part of the previous
 * or next high signal will be mixed there.
 *
 * Applying our simple transformation we make more likely if the current
 * bit is a zero, to detect another zero. Symmetrically if it is a one
 * it will be more likely to detect a one because of the transformation.
 * In this way similar levels will be interpreted more likely in the
 * correct way. */
void applyPhaseCorrection(uint16_t *m) {
	int j;

	m += 16; /* Skip preamble. */
	for (j = 0; j < (MODES_LONG_MSG_BITS - 1) * 2; j += 2) {
		if (m[j] > m[j + 1]) {
			/* One */
			m[j + 2] = (m[j + 2] * 5) / 4;
		}
		else {
			/* Zero */
			m[j + 2] = (m[j + 2] * 4) / 5;
		}
	}
}

/* Detect a Mode S messages inside the magnitude buffer pointed by 'm' and of
 * size 'mlen' bytes. Every detected Mode S message is convert it into a
 * stream of bits and passed to the function to display it. */
void detectModeS(uint16_t *m, uint32_t mlen) {
	unsigned char bits[MODES_LONG_MSG_BITS];
	unsigned char msg[MODES_LONG_MSG_BITS / 2];
	uint16_t aux[MODES_LONG_MSG_BITS * 2];
	uint32_t j;
	int use_correction = 0;

	/* The Mode S preamble is made of impulses of 0.5 microseconds at
	 * the following time offsets:
	 *
	 * 0   - 0.5 usec: first impulse.
	 * 1.0 - 1.5 usec: second impulse.
	 * 3.5 - 4   usec: third impulse.
	 * 4.5 - 5   usec: last impulse.
	 *
	 * Since we are sampling at 2 Mhz every sample in our magnitude vector
	 * is 0.5 usec, so the preamble will look like this, assuming there is
	 * an impulse at offset 0 in the array:
	 *
	 * 0   -----------------
	 * 1   -
	 * 2   ------------------
	 * 3   --
	 * 4   -
	 * 5   --
	 * 6   -
	 * 7   ------------------
	 * 8   --
	 * 9   -------------------
	 */
	for (j = 0; j < mlen - MODES_FULL_LEN * 2; j++) {
		int low, high, delta, i, errors;
		int good_message = 0;

		if (use_correction) goto good_preamble; /* We already checked it. */

		/* First check of relations between the first 10 samples
		 * representing a valid preamble. We don't even investigate further
		 * if this simple test is not passed. */
		if (!(m[j] > m[j + 1] &&
					m[j + 1] < m[j + 2] &&
					m[j + 2] > m[j + 3] &&
					m[j + 3] < m[j] &&
					m[j + 4] < m[j] &&
					m[j + 5] < m[j] &&
					m[j + 6] < m[j] &&
					m[j + 7] > m[j + 8] &&
					m[j + 8] < m[j + 9] &&
					m[j + 9] > m[j + 6]))
		{
			if (Modes.debug & MODES_DEBUG_NOPREAMBLE &&
					m[j] > MODES_DEBUG_NOPREAMBLE_LEVEL)
				dumpRawMessage("Unexpected ratio among first 10 samples",
						msg, m, j);
			continue;
		}

		/* The samples between the two spikes must be < than the average
		 * of the high spikes level. We don't test bits too near to
		 * the high levels as signals can be out of phase so part of the
		 * energy can be in the near samples. */
		high = (m[j] + m[j + 2] + m[j + 7] + m[j + 9]) / 6;
		if (m[j + 4] >= high ||
				m[j + 5] >= high)
		{
			if (Modes.debug & MODES_DEBUG_NOPREAMBLE &&
					m[j] > MODES_DEBUG_NOPREAMBLE_LEVEL)
				dumpRawMessage(
						"Too high level in samples between 3 and 6",
						msg, m, j);
			continue;
		}

		/* Similarly samples in the range 11-14 must be low, as it is the
		 * space between the preamble and real data. Again we don't test
		 * bits too near to high levels, see above. */
		if (m[j + 11] >= high ||
				m[j + 12] >= high ||
				m[j + 13] >= high ||
				m[j + 14] >= high)
		{
			if (Modes.debug & MODES_DEBUG_NOPREAMBLE &&
					m[j] > MODES_DEBUG_NOPREAMBLE_LEVEL)
				dumpRawMessage(
						"Too high level in samples between 10 and 15",
						msg, m, j);
			continue;
		}
		Modes.stat_valid_preamble++;

good_preamble:
		/* If the previous attempt with this message failed, retry using
		 * magnitude correction. */
		if (use_correction) {
			memcpy(aux, m + j + MODES_PREAMBLE_US * 2, sizeof(aux));
			if (j && detectOutOfPhase(m + j)) {
				applyPhaseCorrection(m + j);
				Modes.stat_out_of_phase++;
			}
			/* TODO ... apply other kind of corrections. */
		}

		/* Decode all the next 112 bits, regardless of the actual message
		 * size. We'll check the actual message type later. */
		errors = 0;
		for (i = 0; i < MODES_LONG_MSG_BITS * 2; i += 2) {
			low = m[j + i + MODES_PREAMBLE_US * 2];
			high = m[j + i + MODES_PREAMBLE_US * 2 + 1];
			delta = low - high;
			if (delta < 0) delta = -delta;

			if (i > 0 && delta < 256) {
				bits[i / 2] = bits[i / 2 - 1];
			}
			else if (low == high) {
				/* Checking if two adiacent samples have the same magnitude
				 * is an effective way to detect if it's just random noise
				 * that was detected as a valid preamble. */
				bits[i / 2] = 2; /* error */
				if (i < MODES_SHORT_MSG_BITS * 2) errors++;
			}
			else if (low > high) {
				bits[i / 2] = 1;
			}
			else {
				/* (low < high) for exclusion  */
				bits[i / 2] = 0;
			}
		}

		/* Restore the original message if we used magnitude correction. */
		if (use_correction)
			memcpy(m + j + MODES_PREAMBLE_US * 2, aux, sizeof(aux));

		/* Pack bits into bytes */
		for (i = 0; i < MODES_LONG_MSG_BITS; i += 8) {
			msg[i / 8] =
				bits[i] << 7 |
				bits[i + 1] << 6 |
				bits[i + 2] << 5 |
				bits[i + 3] << 4 |
				bits[i + 4] << 3 |
				bits[i + 5] << 2 |
				bits[i + 6] << 1 |
				bits[i + 7];
		}

		int msgtype = msg[0] >> 3;
		int msglen = modesMessageLenByType(msgtype) / 8;

		/* Last check, high and low bits are different enough in magnitude
		 * to mark this as real message and not just noise? */
		delta = 0;
		for (i = 0; i < msglen * 8 * 2; i += 2) {
			delta += abs(m[j + i + MODES_PREAMBLE_US * 2] -
					m[j + i + MODES_PREAMBLE_US * 2 + 1]);
		}
		delta /= msglen * 4;

		/* Filter for an average delta of three is small enough to let almost
		 * every kind of message to pass, but high enough to filter some
		 * random noise. */
		if (delta < 10 * 255) {
			use_correction = 0;
			continue;
		}

		/* If we reached this point, and error is zero, we are very likely
		 * with a Mode S message in our hands, but it may still be broken
		 * and CRC may not be correct. This is handled by the next layer. */
		if (errors == 0 || (Modes.aggressive && errors < 3)) {
			struct modesMessage mm;

			/* Decode the received message and update statistics */
			decodeModesMessage(&mm, msg);

			/* Update statistics. */
			if (mm.crcok || use_correction) {
				if (errors == 0) Modes.stat_demodulated++;
				if (mm.errorbit == -1) {
					if (mm.crcok)
						Modes.stat_goodcrc++;
					else
						Modes.stat_badcrc++;
				}
				else {
					Modes.stat_badcrc++;
					Modes.stat_fixed++;
					if (mm.errorbit < MODES_LONG_MSG_BITS)
						Modes.stat_single_bit_fix++;
					else
						Modes.stat_two_bits_fix++;
				}
			}

			/* Output debug mode info if needed. */
			if (use_correction == 0) {
				if (Modes.debug & MODES_DEBUG_DEMOD)
					dumpRawMessage("Demodulated with 0 errors", msg, m, j);
				else if (Modes.debug & MODES_DEBUG_BADCRC &&
						mm.msgtype == 17 &&
						(!mm.crcok || mm.errorbit != -1))
					dumpRawMessage("Decoded with bad CRC", msg, m, j);
				else if (Modes.debug & MODES_DEBUG_GOODCRC && mm.crcok &&
						mm.errorbit == -1)
					dumpRawMessage("Decoded with good CRC", msg, m, j);
			}

			/* Skip this message if we are sure it's fine. */
			if (mm.crcok) {
				j += (MODES_PREAMBLE_US + (msglen * 8)) * 2;
				good_message = 1;
				if (use_correction)
					mm.phase_corrected = 1;
			}

			/* Pass data to the next layer */
			useModesMessage(&mm);
		}
		else {
			if (Modes.debug & MODES_DEBUG_DEMODERR && use_correction) {
				printf("The following message has %d demod errors\n", errors);
				dumpRawMessage("Demodulated with errors", msg, m, j);
			}
		}

		/* Retry with phase correction if possible. */
		if (!good_message && !use_correction) {
			j--;
			use_correction = 1;
		}
		else {
			use_correction = 0;
		}
	}
}

/* When a new message is available, because it was decoded from the
 * RTL device, file, or received in the TCP input port, or any other
 * way we can receive a decoded message, we call this function in order
 * to use the message.
 *
 * Basically this function passes a raw message to the upper layers for
 * further processing and visualization. */
void useModesMessage(struct modesMessage *mm) {
	if (!Modes.stats && (Modes.check_crc == 0 || mm->crcok)) {
		/* Track aircrafts in interactive mode or if the HTTP
		 * interface is enabled. */
		if (Modes.interactive || Modes.stat_http_requests > 0 || Modes.stat_sbs_connections > 0) {
			struct aircraft *a = interactiveReceiveData(mm);
			if (a && Modes.stat_sbs_connections > 0) modesSendSBSOutput(mm, a);  /* Feed SBS output clients. */
		}
		/* In non-interactive way, display messages on standard output. */
		if (!Modes.interactive) {
			displayModesMessage(mm);
			if (!Modes.raw && !Modes.onlyaddr) printf("\n");
		}
		/* Send data to connected clients. */
		if (Modes.net) {
			modesSendRawOutput(mm);  /* Feed raw output clients. */
		}
	}
}

/* ========================= Interactive mode =============================== */

/* Return a new aircraft structure for the interactive mode linked list
 * of aircrafts. */
struct aircraft *interactiveCreateAircraft(uint32_t addr) {
	struct aircraft *a = malloc(sizeof(*a));

	a->addr = addr;
	snprintf(a->hexaddr, sizeof(a->hexaddr), "%06x", (int)addr);
	a->flight[0] = '\0';
	a->altitude = 0;
	a->speed = 0;
	a->track = 0;
	a->odd_cprlat = 0;
	a->odd_cprlon = 0;
	a->odd_cprtime = 0;
	a->even_cprlat = 0;
	a->even_cprlon = 0;
	a->even_cprtime = 0;
	a->lat = 0;
	a->lon = 0;
	a->seen = time(NULL);
	a->messages = 0;
	a->next = NULL;
	return a;
}

/* Return the aircraft with the specified address, or NULL if no aircraft
 * exists with this address. */
struct aircraft *interactiveFindAircraft(uint32_t addr) {
	struct aircraft *a = Modes.aircrafts;

	while (a) {
		if (a->addr == addr) return a;
		a = a->next;
	}
	return NULL;
}

/* Always positive MOD operation, used for CPR decoding. */
int cprModFunction(int a, int b) {
	int res = a % b;
	if (res < 0) res += b;
	return res;
}

/* The NL function uses the precomputed table from 1090-WP-9-14 */
int cprNLFunction(double lat) {
	if (lat < 0) lat = -lat; /* Table is simmetric about the equator. */
	if (lat < 10.47047130) return 59;
	if (lat < 14.82817437) return 58;
	if (lat < 18.18626357) return 57;
	if (lat < 21.02939493) return 56;
	if (lat < 23.54504487) return 55;
	if (lat < 25.82924707) return 54;
	if (lat < 27.93898710) return 53;
	if (lat < 29.91135686) return 52;
	if (lat < 31.77209708) return 51;
	if (lat < 33.53993436) return 50;
	if (lat < 35.22899598) return 49;
	if (lat < 36.85025108) return 48;
	if (lat < 38.41241892) return 47;
	if (lat < 39.92256684) return 46;
	if (lat < 41.38651832) return 45;
	if (lat < 42.80914012) return 44;
	if (lat < 44.19454951) return 43;
	if (lat < 45.54626723) return 42;
	if (lat < 46.86733252) return 41;
	if (lat < 48.16039128) return 40;
	if (lat < 49.42776439) return 39;
	if (lat < 50.67150166) return 38;
	if (lat < 51.89342469) return 37;
	if (lat < 53.09516153) return 36;
	if (lat < 54.27817472) return 35;
	if (lat < 55.44378444) return 34;
	if (lat < 56.59318756) return 33;
	if (lat < 57.72747354) return 32;
	if (lat < 58.84763776) return 31;
	if (lat < 59.95459277) return 30;
	if (lat < 61.04917774) return 29;
	if (lat < 62.13216659) return 28;
	if (lat < 63.20427479) return 27;
	if (lat < 64.26616523) return 26;
	if (lat < 65.31845310) return 25;
	if (lat < 66.36171008) return 24;
	if (lat < 67.39646774) return 23;
	if (lat < 68.42322022) return 22;
	if (lat < 69.44242631) return 21;
	if (lat < 70.45451075) return 20;
	if (lat < 71.45986473) return 19;
	if (lat < 72.45884545) return 18;
	if (lat < 73.45177442) return 17;
	if (lat < 74.43893416) return 16;
	if (lat < 75.42056257) return 15;
	if (lat < 76.39684391) return 14;
	if (lat < 77.36789461) return 13;
	if (lat < 78.33374083) return 12;
	if (lat < 79.29428225) return 11;
	if (lat < 80.24923213) return 10;
	if (lat < 81.19801349) return 9;
	if (lat < 82.13956981) return 8;
	if (lat < 83.07199445) return 7;
	if (lat < 83.99173563) return 6;
	if (lat < 84.89166191) return 5;
	if (lat < 85.75541621) return 4;
	if (lat < 86.53536998) return 3;
	if (lat < 87.00000000) return 2;
	else return 1;
}

int cprNFunction(double lat, int isodd) {
	int nl = cprNLFunction(lat) - isodd;
	if (nl < 1) nl = 1;
	return nl;
}

double cprDlonFunction(double lat, int isodd) {
	return 360.0 / cprNFunction(lat, isodd);
}

/* This algorithm comes from:
 * http://www.lll.lu/~edward/edward/adsb/DecodingADSBposition.html.
 *
 *
 * A few remarks:
 * 1) 131072 is 2^17 since CPR latitude and longitude are encoded in 17 bits.
 * 2) We assume that we always received the odd packet as last packet for
 *    simplicity. This may provide a position that is less fresh of a few
 *    seconds.
 */
void decodeCPR(struct aircraft *a) {
	const double AirDlat0 = 360.0 / 60;
	const double AirDlat1 = 360.0 / 59;
	double lat0 = a->even_cprlat;
	double lat1 = a->odd_cprlat;
	double lon0 = a->even_cprlon;
	double lon1 = a->odd_cprlon;

	/* Compute the Latitude Index "j" */
	int j = floor(((59 * lat0 - 60 * lat1) / 131072) + 0.5);
	double rlat0 = AirDlat0 * (cprModFunction(j, 60) + lat0 / 131072);
	double rlat1 = AirDlat1 * (cprModFunction(j, 59) + lat1 / 131072);

	if (rlat0 >= 270) rlat0 -= 360;
	if (rlat1 >= 270) rlat1 -= 360;

	/* Check that both are in the same latitude zone, or abort. */
	if (cprNLFunction(rlat0) != cprNLFunction(rlat1)) return;

	/* Compute ni and the longitude index m */
	if (a->even_cprtime > a->odd_cprtime) {
		/* Use even packet. */
		int ni = cprNFunction(rlat0, 0);
		int m = floor((((lon0 * (cprNLFunction(rlat0) - 1)) -
						(lon1 * cprNLFunction(rlat0))) / 131072) + 0.5);
		a->lon = cprDlonFunction(rlat0, 0) * (cprModFunction(m, ni) + lon0 / 131072);
		a->lat = rlat0;
	}
	else {
		/* Use odd packet. */
		int ni = cprNFunction(rlat1, 1);
		int m = floor((((lon0 * (cprNLFunction(rlat1) - 1)) -
						(lon1 * cprNLFunction(rlat1))) / 131072.0) + 0.5);
		a->lon = cprDlonFunction(rlat1, 1) * (cprModFunction(m, ni) + lon1 / 131072);
		a->lat = rlat1;
	}
	if (a->lon > 180) a->lon -= 360;
}

/* Receive new messages and populate the interactive mode with more info. */
struct aircraft *interactiveReceiveData(struct modesMessage *mm) {
	uint32_t addr;
	struct aircraft *a, *aux;

	if (Modes.check_crc && mm->crcok == 0) return NULL;
	addr = (mm->aa1 << 16) | (mm->aa2 << 8) | mm->aa3;

	/* Loookup our aircraft or create a new one. */
	a = interactiveFindAircraft(addr);
	if (!a) {
		a = interactiveCreateAircraft(addr);
		a->next = Modes.aircrafts;
		Modes.aircrafts = a;
	}
	else {
		/* If it is an already known aircraft, move it on head
		 * so we keep aircrafts ordered by received message time.
		 *
		 * However move it on head only if at least one second elapsed
		 * since the aircraft that is currently on head sent a message,
		 * othewise with multiple aircrafts at the same time we have an
		 * useless shuffle of positions on the screen. */
		if (0 && Modes.aircrafts != a && (time(NULL) - a->seen) >= 1) {
			aux = Modes.aircrafts;
			while (aux->next != a) aux = aux->next;
			/* Now we are a node before the aircraft to remove. */
			aux->next = aux->next->next; /* removed. */
			/* Add on head */
			a->next = Modes.aircrafts;
			Modes.aircrafts = a;
		}
	}

	a->seen = time(NULL);
	a->messages++;

	if (mm->msgtype == 0 || mm->msgtype == 4 || mm->msgtype == 20) {
		a->altitude = mm->altitude;
	}
	else if (mm->msgtype == 17) {
		if (mm->metype >= 1 && mm->metype <= 4) {
			memcpy(a->flight, mm->flight, sizeof(a->flight));
		}
		else if (mm->metype >= 9 && mm->metype <= 18) {
			a->altitude = mm->altitude;
			if (mm->fflag) {
				a->odd_cprlat = mm->raw_latitude;
				a->odd_cprlon = mm->raw_longitude;
				a->odd_cprtime = mstime();
			}
			else {
				a->even_cprlat = mm->raw_latitude;
				a->even_cprlon = mm->raw_longitude;
				a->even_cprtime = mstime();
			}
			/* If the two data is less than 10 seconds apart, compute
			 * the position. */
			if (abs(a->even_cprtime - a->odd_cprtime) <= 10000) {
				decodeCPR(a);
			}
		}
		else if (mm->metype == 19) {
			if (mm->mesub == 1 || mm->mesub == 2) {
				a->speed = mm->velocity;
				a->track = mm->heading;
			}
		}
	}
	return a;
}

/* Show the currently captured interactive data on screen. */
void interactiveShowData(void) {
	struct aircraft *a = Modes.aircrafts;
	time_t now = time(NULL);
	char progress[4];
	int count = 0;

	memset(progress, ' ', 3);
	progress[time(NULL) % 3] = '.';
	progress[3] = '\0';

	printf("\x1b[H\x1b[2J");    /* Clear the screen */
	printf(
			"Hex    Flight   Altitude  Speed   Lat       Lon       Track  Messages Seen %s\n"
			"--------------------------------------------------------------------------------\n",
			progress);

	while (a && count < Modes.interactive_rows) {
		int altitude = a->altitude, speed = a->speed;

		/* Convert units to metric if --metric was specified. */
		if (Modes.metric) {
			altitude /= 3.2828;
			speed *= 1.852;
		}

		printf("%-6s %-8s %-9d %-7d %-7.03f   %-7.03f   %-3d   %-9ld %d sec\n",
				a->hexaddr, a->flight, altitude, speed,
				a->lat, a->lon, a->track, a->messages,
				(int)(now - a->seen));
		a = a->next;
		count++;
	}
}

/* When in interactive mode If we don't receive new nessages within
 * MODES_INTERACTIVE_TTL seconds we remove the aircraft from the list. */
void interactiveRemoveStaleAircrafts(void) {
	struct aircraft *a = Modes.aircrafts;
	struct aircraft *prev = NULL;
	time_t now = time(NULL);

	while (a) {
		if ((now - a->seen) > Modes.interactive_ttl) {
			struct aircraft *next = a->next;
			/* Remove the element from the linked list, with care
			 * if we are removing the first element. */
			free(a);
			if (!prev)
				Modes.aircrafts = next;
			else
				prev->next = next;
			a = next;
		}
		else {
			prev = a;
			a = a->next;
		}
	}
}

/* ============================== Snip mode ================================= */

/* Get raw IQ samples and filter everything is < than the specified level
 * for more than 256 samples in order to reduce example file size. */
void snipMode(int level) {
	int i, q;
	long long c = 0;

	while ((i = getchar()) != EOF && (q = getchar()) != EOF) {
		if (abs(i - 127) < level && abs(q - 127) < level) {
			c++;
			if (c > MODES_PREAMBLE_US * 4) continue;
		}
		else {
			c = 0;
		}
		putchar(i);
		putchar(q);
	}
}

/* ============================= Networking =================================
 * Note: here we risregard any kind of good coding practice in favor of
 * extreme simplicity, that is:
 *
 * 1) We only rely on the kernel buffers for our I/O without any kind of
 *    user space buffering.
 * 2) We don't register any kind of event handler, from time to time a
 *    function gets called and we accept new connections. All the rest is
 *    handled via non-blocking I/O and manually pulling clients to see if
 *    they have something new to share with us when reading is needed.
 */

#define MODES_NET_SERVICE_RAWO 0
#define MODES_NET_SERVICE_RAWI 1
#define MODES_NET_SERVICE_HTTP 2
#define MODES_NET_SERVICE_SBS 3
#define MODES_NET_SERVICES_NUM 4
struct {
	char *descr;
	int *socket;
	int port;
} modesNetServices[MODES_NET_SERVICES_NUM] = {
	{ "Raw TCP output", &Modes.ros, MODES_NET_OUTPUT_RAW_PORT },
	{ "Raw TCP input", &Modes.ris, MODES_NET_INPUT_RAW_PORT },
	{ "HTTP server", &Modes.https, MODES_NET_HTTP_PORT },
	{ "Basestation TCP output", &Modes.sbsos, MODES_NET_OUTPUT_SBS_PORT }
};

/* Networking "stack" initialization. */
void modesInitNet(void) {
	int j;

	memset(Modes.clients, 0, sizeof(Modes.clients));
	Modes.maxfd = -1;

	for (j = 0; j < MODES_NET_SERVICES_NUM; j++) {
		int s = anetTcpServer(Modes.aneterr, modesNetServices[j].port, NULL);
		if (s == -1) {
			fprintf(stderr, "Error opening the listening port %d (%s): %s\n",
					modesNetServices[j].port,
					modesNetServices[j].descr,
					strerror(errno));
			exit(1);
		}
		anetNonBlock(Modes.aneterr, s);
		*modesNetServices[j].socket = s;
	}

	signal(SIGPIPE, SIG_IGN);
}

/* This function gets called from time to time when the decoding thread is
 * awakened by new data arriving. This usually happens a few times every
 * second. */
void modesAcceptClients(void) {
	int fd, port;
	unsigned int j;
	struct client *c;

	for (j = 0; j < MODES_NET_SERVICES_NUM; j++) {
		fd = anetTcpAccept(Modes.aneterr, *modesNetServices[j].socket,
				NULL, &port);
		if (fd == -1) {
			if (Modes.debug & MODES_DEBUG_NET && errno != EAGAIN)
				printf("Accept %d: %s\n", *modesNetServices[j].socket,
						strerror(errno));
			continue;
		}

		if (fd >= MODES_NET_MAX_FD) {
			close(fd);
			return; /* Max number of clients reached. */
		}

		anetNonBlock(Modes.aneterr, fd);
		c = malloc(sizeof(*c));
		c->service = *modesNetServices[j].socket;
		c->fd = fd;
		c->buflen = 0;
		Modes.clients[fd] = c;
		anetSetSendBuffer(Modes.aneterr, fd, MODES_NET_SNDBUF_SIZE);

		if (Modes.maxfd < fd) Modes.maxfd = fd;
		if (*modesNetServices[j].socket == Modes.sbsos)
			Modes.stat_sbs_connections++;

		j--; /* Try again with the same listening port. */

		if (Modes.debug & MODES_DEBUG_NET)
			printf("Created new client %d\n", fd);
	}
}

/* On error free the client, collect the structure, adjust maxfd if needed. */
void modesFreeClient(int fd) {
	close(fd);
	free(Modes.clients[fd]);
	Modes.clients[fd] = NULL;

	if (Modes.debug & MODES_DEBUG_NET)
		printf("Closing client %d\n", fd);

	/* If this was our maxfd, scan the clients array to find the new max.
	 * Note that we are sure there is no active fd greater than the closed
	 * fd, so we scan from fd-1 to 0. */
	if (Modes.maxfd == fd) {
		int j;

		Modes.maxfd = -1;
		for (j = fd - 1; j >= 0; j--) {
			if (Modes.clients[j]) {
				Modes.maxfd = j;
				break;
			}
		}
	}
}

/* Send the specified message to all clients listening for a given service. */
void modesSendAllClients(int service, void *msg, int len) {
	int j;
	struct client *c;

	for (j = 0; j <= Modes.maxfd; j++) {
		c = Modes.clients[j];
		if (c && c->service == service) {
			int nwritten = write(j, msg, len);
			if (nwritten != len) {
				modesFreeClient(j);
			}
		}
	}
}

/* Write raw output to TCP clients. */
void modesSendRawOutput(struct modesMessage *mm) {
	char msg[128], *p = msg;
	int j;

	*p++ = '*';
	for (j = 0; j < mm->msgbits / 8; j++) {
		sprintf(p, "%02X", mm->msg[j]);
		p += 2;
	}
	*p++ = ';';
	*p++ = '\n';
	modesSendAllClients(Modes.ros, msg, p - msg);
}


/* Write SBS output to TCP clients. */
void modesSendSBSOutput(struct modesMessage *mm, struct aircraft *a) {
	char msg[256], *p = msg;
	int emergency = 0, ground = 0, alert = 0, spi = 0;

	if (mm->msgtype == 4 || mm->msgtype == 5 || mm->msgtype == 21) {
		/* Node: identity is calculated/kept in base10 but is actually
		 * octal (07500 is represented as 7500) */
		if (mm->identity == 7500 || mm->identity == 7600 ||
				mm->identity == 7700) emergency = -1;
		if (mm->fs == 1 || mm->fs == 3) ground = -1;
		if (mm->fs == 2 || mm->fs == 3 || mm->fs == 4) alert = -1;
		if (mm->fs == 4 || mm->fs == 5) spi = -1;
	}

	if (mm->msgtype == 0) {
		p += sprintf(p, "MSG,5,,,%02X%02X%02X,,,,,,,%d,,,,,,,,,,",
				mm->aa1, mm->aa2, mm->aa3, mm->altitude);
	}
	else if (mm->msgtype == 4) {
		p += sprintf(p, "MSG,5,,,%02X%02X%02X,,,,,,,%d,,,,,,,%d,%d,%d,%d",
				mm->aa1, mm->aa2, mm->aa3, mm->altitude, alert, emergency, spi, ground);
	}
	else if (mm->msgtype == 5) {
		p += sprintf(p, "MSG,6,,,%02X%02X%02X,,,,,,,,,,,,,%d,%d,%d,%d,%d",
				mm->aa1, mm->aa2, mm->aa3, mm->identity, alert, emergency, spi, ground);
	}
	else if (mm->msgtype == 11) {
		p += sprintf(p, "MSG,8,,,%02X%02X%02X,,,,,,,,,,,,,,,,,",
				mm->aa1, mm->aa2, mm->aa3);
	}
	else if (mm->msgtype == 17 && mm->metype == 4) {
		p += sprintf(p, "MSG,1,,,%02X%02X%02X,,,,,,%s,,,,,,,,0,0,0,0",
				mm->aa1, mm->aa2, mm->aa3, mm->flight);
	}
	else if (mm->msgtype == 17 && mm->metype >= 9 && mm->metype <= 18) {
		if (a->lat == 0 && a->lon == 0)
			p += sprintf(p, "MSG,3,,,%02X%02X%02X,,,,,,,%d,,,,,,,0,0,0,0",
					mm->aa1, mm->aa2, mm->aa3, mm->altitude);
		else
			p += sprintf(p, "MSG,3,,,%02X%02X%02X,,,,,,,%d,,,%1.5f,%1.5f,,,"
					"0,0,0,0",
					mm->aa1, mm->aa2, mm->aa3, mm->altitude, a->lat, a->lon);
	}
	else if (mm->msgtype == 17 && mm->metype == 19 && mm->mesub == 1) {
		int vr = (mm->vert_rate_sign == 0 ? 1 : -1) * (mm->vert_rate - 1) * 64;

		p += sprintf(p, "MSG,4,,,%02X%02X%02X,,,,,,,,%d,%d,,,%i,,0,0,0,0",
				mm->aa1, mm->aa2, mm->aa3, a->speed, a->track, vr);
	}
	else if (mm->msgtype == 21) {
		p += sprintf(p, "MSG,6,,,%02X%02X%02X,,,,,,,,,,,,,%d,%d,%d,%d,%d",
				mm->aa1, mm->aa2, mm->aa3, mm->identity, alert, emergency, spi, ground);
	}
	else {
		return;
	}

	*p++ = '\n';
	modesSendAllClients(Modes.sbsos, msg, p - msg);
}

/* Turn an hex digit into its 4 bit decimal value.
 * Returns -1 if the digit is not in the 0-F range. */
int hexDigitVal(int c) {
	c = tolower(c);
	if (c >= '0' && c <= '9') return c - '0';
	else if (c >= 'a' && c <= 'f') return c - 'a' + 10;
	else return -1;
}

/* This function decodes a string representing a Mode S message in
 * raw hex format like: *8D4B969699155600E87406F5B69F;
 * The string is supposed to be at the start of the client buffer
 * and null-terminated.
 *
 * The message is passed to the higher level layers, so it feeds
 * the selected screen output, the network output and so forth.
 *
 * If the message looks invalid is silently discarded.
 *
 * The function always returns 0 (success) to the caller as there is
 * no case where we want broken messages here to close the client
 * connection. */
int decodeHexMessage(struct client *c) {
	char *hex = c->buf;
	int l = strlen(hex), j;
	unsigned char msg[MODES_LONG_MSG_BYTES];
	struct modesMessage mm;

	/* Remove spaces on the left and on the right. */
	while (l && isspace(hex[l - 1])) {
		hex[l - 1] = '\0';
		l--;
	}
	while (isspace(*hex)) {
		hex++;
		l--;
	}

	/* Turn the message into binary. */
	if (l < 2 || hex[0] != '*' || hex[l - 1] != ';') return 0;
	hex++; l -= 2; /* Skip * and ; */
	if (l > MODES_LONG_MSG_BYTES * 2) return 0; /* Too long message... broken. */
	for (j = 0; j < l; j += 2) {
		int high = hexDigitVal(hex[j]);
		int low = hexDigitVal(hex[j + 1]);

		if (high == -1 || low == -1) return 0;
		msg[j / 2] = (high << 4) | low;
	}
	decodeModesMessage(&mm, msg);
	useModesMessage(&mm);
	return 0;
}

/* Return a description of planes in json. */
char *aircraftsToJson(int *len) {
	struct aircraft *a = Modes.aircrafts;
	int buflen = 1024; /* The initial buffer is incremented as needed. */
	char *buf = malloc(buflen), *p = buf;
	int l;

	l = snprintf(p, buflen, "[\n");
	p += l; buflen -= l;
	while (a) {
		int altitude = a->altitude, speed = a->speed;

		/* Convert units to metric if --metric was specified. */
		if (Modes.metric) {
			altitude /= 3.2828;
			speed *= 1.852;
		}

		if (a->lat != 0 && a->lon != 0) {
			l = snprintf(p, buflen,
					"{\"hex\":\"%s\", \"flight\":\"%s\", \"lat\":%f, "
					"\"lon\":%f, \"altitude\":%d, \"track\":%d, "
					"\"speed\":%d},\n",
					a->hexaddr, a->flight, a->lat, a->lon, a->altitude, a->track,
					a->speed);
			p += l; buflen -= l;
			/* Resize if needed. */
			if (buflen < 256) {
				int used = p - buf;
				buflen += 1024; /* Our increment. */
				buf = realloc(buf, used + buflen);
				p = buf + used;
			}
		}
		a = a->next;
	}
	/* Remove the final comma if any, and closes the json array. */
	if (*(p - 2) == ',') {
		*(p - 2) = '\n';
		p--;
		buflen++;
	}
	l = snprintf(p, buflen, "]\n");
	p += l; buflen -= l;

	*len = p - buf;
	return buf;
}

#define MODES_CONTENT_TYPE_HTML "text/html;charset=utf-8"
#define MODES_CONTENT_TYPE_JSON "application/json;charset=utf-8"

/* Get an HTTP request header and write the response to the client.
 * Again here we assume that the socket buffer is enough without doing
 * any kind of userspace buffering.
 *
 * Returns 1 on error to signal the caller the client connection should
 * be closed. */
int handleHTTPRequest(struct client *c) {
	char hdr[512];
	int clen, hdrlen;
	int httpver, keepalive;
	char *p, *url, *content;
	char *ctype;

	if (Modes.debug & MODES_DEBUG_NET)
		printf("\nHTTP request: %s\n", c->buf);

	/* Minimally parse the request. */
	httpver = (strstr(c->buf, "HTTP/1.1") != NULL) ? 11 : 10;
	if (httpver == 10) {
		/* HTTP 1.0 defaults to close, unless otherwise specified. */
		keepalive = strstr(c->buf, "Connection: keep-alive") != NULL;
	}
	else if (httpver == 11) {
		/* HTTP 1.1 defaults to keep-alive, unless close is specified. */
		keepalive = strstr(c->buf, "Connection: close") == NULL;
	}

	/* Identify he URL. */
	p = strchr(c->buf, ' ');
	if (!p) return 1; /* There should be the method and a space... */
	url = ++p; /* Now this should point to the requested URL. */
	p = strchr(p, ' ');
	if (!p) return 1; /* There should be a space before HTTP/... */
	*p = '\0';

	if (Modes.debug & MODES_DEBUG_NET) {
		printf("\nHTTP keep alive: %d\n", keepalive);
		printf("HTTP requested URL: %s\n\n", url);
	}

	/* Select the content to send, we have just two so far:
	 * "/" -> Our google map application.
	 * "/data.json" -> Our ajax request to update planes. */
	if (strstr(url, "/data.json")) {
		content = aircraftsToJson(&clen);
		ctype = MODES_CONTENT_TYPE_JSON;
	}
	else {

		if(ghtmlSize!=0){

			clen=ghtmlSize;
			content = malloc(ghtmlSize);
			memcpy(content,ghtmlData,ghtmlSize);

		}else{

			char buf[128];
			clen = snprintf(buf, sizeof(buf), "Error opening HTML file: %s",
					strerror(errno));
			content = strdup(buf);

		}
		ctype = MODES_CONTENT_TYPE_HTML;
	}

	/* Create the header and send the reply. */
	hdrlen = snprintf(hdr, sizeof(hdr),
			"HTTP/1.1 200 OK\r\n"
			"Server: Dump1090\r\n"
			"Content-Type: %s\r\n"
			"Connection: %s\r\n"
			"Content-Length: %d\r\n"
			"Access-Control-Allow-Origin: *\r\n"
			"\r\n",
			ctype,
			keepalive ? "keep-alive" : "close",
			clen);

	if (Modes.debug & MODES_DEBUG_NET)
		printf("HTTP Reply header:\n%s", hdr);

	/* Send header and content. */
	if (write(c->fd, hdr, hdrlen) != hdrlen ||
			write(c->fd, content, clen) != clen)
	{
		free(content);
		return 1;
	}
	free(content);
	Modes.stat_http_requests++;
	return !keepalive;
}

/* This function polls the clients using read() in order to receive new
 * messages from the net.
 *
 * The message is supposed to be separated by the next message by the
 * separator 'sep', that is a null-terminated C string.
 *
 * Every full message received is decoded and passed to the higher layers
 * calling the function 'handler'.
 *
 * The handelr returns 0 on success, or 1 to signal this function we
 * should close the connection with the client in case of non-recoverable
 * errors. */
void modesReadFromClient(struct client *c, char *sep,
		int(*handler)(struct client *))
{
	while (1) {
		int left = MODES_CLIENT_BUF_SIZE - c->buflen;
		int nread = read(c->fd, c->buf + c->buflen, left);
		int fullmsg = 0;
		int i;
		char *p;

		if (nread <= 0) {
			if (nread == 0 || errno != EAGAIN) {
				/* Error, or end of file. */
				modesFreeClient(c->fd);
			}
			break; /* Serve next client. */
		}
		c->buflen += nread;

		/* Always null-term so we are free to use strstr() */
		c->buf[c->buflen] = '\0';

		/* If there is a complete message there must be the separator 'sep'
		 * in the buffer, note that we full-scan the buffer at every read
		 * for simplicity. */
		while ((p = strstr(c->buf, sep)) != NULL) {
			i = p - c->buf; /* Turn it as an index inside the buffer. */
			c->buf[i] = '\0'; /* Te handler expects null terminated strings. */
			/* Call the function to process the message. It returns 1
			 * on error to signal we should close the client connection. */
			if (handler(c)) {
				modesFreeClient(c->fd);
				return;
			}
			/* Move what's left at the start of the buffer. */
			i += strlen(sep); /* The separator is part of the previous msg. */
			memmove(c->buf, c->buf + i, c->buflen - i);
			c->buflen -= i;
			c->buf[c->buflen] = '\0';
			/* Maybe there are more messages inside the buffer.
			 * Start looping from the start again. */
			fullmsg = 1;
		}
		/* If our buffer is full discard it, this is some badly
		 * formatted shit. */
		if (c->buflen == MODES_CLIENT_BUF_SIZE) {
			c->buflen = 0;
			/* If there is garbage, read more to discard it ASAP. */
			continue;
		}
		/* If no message was decoded process the next client, otherwise
		 * read more data from the same client. */
		if (!fullmsg) break;
	}
}

/* Read data from clients. This function actually delegates a lower-level
 * function that depends on the kind of service (raw, http, ...). */
void modesReadFromClients(void) {
	int j;
	struct client *c;

	for (j = 0; j <= Modes.maxfd; j++) {
		if ((c = Modes.clients[j]) == NULL) continue;
		if (c->service == Modes.ris)
			modesReadFromClient(c, "\n", decodeHexMessage);
		else if (c->service == Modes.https)
			modesReadFromClient(c, "\r\n\r\n", handleHTTPRequest);
	}
}

/* This function is used when "net only" mode is enabled to know when there
 * is at least a new client to serve. Note that the dump1090 networking model
 * is extremely trivial and a function takes care of handling all the clients
 * that have something to serve, without a proper event library, so the
 * function here returns as long as there is a single client ready, or
 * when the specified timeout in milliesconds elapsed, without specifying to
 * the caller what client requires to be served. */
void modesWaitReadableClients(int timeout_ms) {
	struct timeval tv;
	fd_set fds;
	int j, maxfd = Modes.maxfd;

	FD_ZERO(&fds);

	/* Set client FDs */
	for (j = 0; j <= Modes.maxfd; j++) {
		if (Modes.clients[j]) FD_SET(j, &fds);
	}

	/* Set listening sockets to accept new clients ASAP. */
	for (j = 0; j < MODES_NET_SERVICES_NUM; j++) {
		int s = *modesNetServices[j].socket;
		FD_SET(s, &fds);
		if (s > maxfd) maxfd = s;
	}

	tv.tv_sec = timeout_ms / 1000;
	tv.tv_usec = (timeout_ms % 1000) * 1000;
	/* We don't care why select returned here, timeout, error, or
	 * FDs ready are all conditions for which we just return. */
	select(maxfd + 1, &fds, NULL, NULL, &tv);
}

/* ============================ Terminal handling  ========================== */

/* Handle resizing terminal. */
void sigWinchCallback() {
	signal(SIGWINCH, SIG_IGN);
	Modes.interactive_rows = getTermRows();
	interactiveShowData();
	signal(SIGWINCH, sigWinchCallback);
}

/* Get the number of rows after the terminal changes size. */
int getTermRows() {
	struct winsize w;
	ioctl(STDOUT_FILENO, TIOCGWINSZ, &w);
	return w.ws_row;
}

/* ================================ Main ==================================== */

void showHelp(void) {
	printf(
			//	"--device-index <index>   Select PlutoSDR device (default: 0).\n"
			"--gain <db>              Set gain (default: auto-gain. Use -100 for auto-gain).\n"
			"--enable-agc             Enable the Automatic Gain Control (default: on).\n"
			"--freq <hz>              Set frequency (default: 1090 Mhz).\n"
			"--ifile <filename>       Read data from file (use '-' for stdin).\n"
			"--interactive            Interactive mode refreshing data on screen.\n"
			"--interactive-rows <num> Max number of rows in interactive mode (default: 15).\n"
			"--interactive-ttl <sec>  Remove from list if idle for <sec> (default: 60).\n"
			"--raw                    Show only messages hex values.\n"
			"--net                    Enable networking.\n"
			"--net-only               Enable just networking, no RTL device or file used.\n"
			"--net-ro-port <port>     TCP listening port for raw output (default: 30002).\n"
			"--net-ri-port <port>     TCP listening port for raw input (default: 30001).\n"
			"--net-http-port <port>   HTTP server port (default: 8080).\n"
			"--net-sbs-port <port>    TCP listening port for BaseStation format output (default: 30003).\n"
			"--no-fix                 Disable single-bits error correction using CRC.\n"
			"--no-crc-check           Disable messages with broken CRC (discouraged).\n"
			"--aggressive             More CPU for more messages (two bits fixes, ...).\n"
			"--stats                  With --ifile print stats at exit. No other output.\n"
			"--onlyaddr               Show only ICAO addresses (testing purposes).\n"
			"--metric                 Use metric units (meters, km/h, ...).\n"
			"--snip <level>           Strip IQ file removing samples < level.\n"
			"--debug <flags>          Debug mode (verbose), see README for details.\n"
			"--help                   Show this help.\n"
			"\n"
			"Debug mode flags: d = Log frames decoded with errors\n"
			"                  D = Log frames decoded with zero errors\n"
			"                  c = Log frames with bad CRC\n"
			"                  C = Log frames with good CRC\n"
			"                  p = Log frames with bad preamble\n"
			"                  n = Log network debugging info\n"
			"                  j = Log frames to frames.js, loadable by debug.html.\n"
			);
}

/* This function is called a few times every second by main in order to
 * perform tasks we need to do continuously, like accepting new clients
 * from the net, refreshing the screen in interactive mode, and so forth. */
void backgroundTasks(void) {
	if (Modes.net) {
		modesAcceptClients();
		modesReadFromClients();
		interactiveRemoveStaleAircrafts();
	}

	/* Refresh screen when in interactive mode. */
	if (Modes.interactive &&
			(mstime() - Modes.interactive_last_update) >
			MODES_INTERACTIVE_REFRESH_TIME)
	{
		interactiveRemoveStaleAircrafts();
		interactiveShowData();
		Modes.interactive_last_update = mstime();
	}
}

int main(int argc, char **argv) {
	int j;
	/* Set sane defaults. */
	modesInitConfig();

	/* Parse the command line options */
	for (j = 1; j < argc; j++) {
		int more = j + 1 < argc; /* There are more arguments. */

		if (!strcmp(argv[j], "--device-index") && more) {
			Modes.dev_index = atoi(argv[++j]);
		}
		else if (!strcmp(argv[j], "--gain") && more) {
			Modes.gain = atof(argv[++j]); /* Gain is in tens of DBs */
		}
		else if (!strcmp(argv[j], "--enable-agc")) {
			Modes.enable_agc=atoi(argv[++j]);
		}
		else if (!strcmp(argv[j], "--freq") && more) {
			Modes.freq = strtoll(argv[++j], NULL, 10);
		}
		else if (!strcmp(argv[j], "--ifile") && more) {
			Modes.filename = strdup(argv[++j]);
		}
		else if (!strcmp(argv[j], "--no-fix")) {
			Modes.fix_errors = 0;
		}
		else if (!strcmp(argv[j], "--no-crc-check")) {
			Modes.check_crc = 0;
		}
		else if (!strcmp(argv[j], "--raw")) {
			Modes.raw = 1;
		}
		else if (!strcmp(argv[j], "--net")) {
			Modes.net = 1;
		}
		else if (!strcmp(argv[j], "--net-only")) {
			Modes.net = 1;
			Modes.net_only = 1;
		}
		else if (!strcmp(argv[j], "--net-ro-port") && more) {
			modesNetServices[MODES_NET_SERVICE_RAWO].port = atoi(argv[++j]);
		}
		else if (!strcmp(argv[j], "--net-ri-port") && more) {
			modesNetServices[MODES_NET_SERVICE_RAWI].port = atoi(argv[++j]);
		}
		else if (!strcmp(argv[j], "--net-http-port") && more) {
			modesNetServices[MODES_NET_SERVICE_HTTP].port = atoi(argv[++j]);
		}
		else if (!strcmp(argv[j], "--net-sbs-port") && more) {
			modesNetServices[MODES_NET_SERVICE_SBS].port = atoi(argv[++j]);
		}
		else if (!strcmp(argv[j], "--onlyaddr")) {
			Modes.onlyaddr = 1;
		}
		else if (!strcmp(argv[j], "--metric")) {
			Modes.metric = 1;
		}
		else if (!strcmp(argv[j], "--aggressive")) {
			Modes.aggressive++;
		}
		else if (!strcmp(argv[j], "--interactive")) {
			Modes.interactive = 1;
		}
		else if (!strcmp(argv[j], "--interactive-rows")) {
			Modes.interactive_rows = atoi(argv[++j]);
		}
		else if (!strcmp(argv[j], "--interactive-ttl")) {
			Modes.interactive_ttl = atoi(argv[++j]);
		}
		else if (!strcmp(argv[j], "--debug") && more) {
			char *f = argv[++j];
			while (*f) {
				switch (*f) {
					case 'D': Modes.debug |= MODES_DEBUG_DEMOD; break;
					case 'd': Modes.debug |= MODES_DEBUG_DEMODERR; break;
					case 'C': Modes.debug |= MODES_DEBUG_GOODCRC; break;
					case 'c': Modes.debug |= MODES_DEBUG_BADCRC; break;
					case 'p': Modes.debug |= MODES_DEBUG_NOPREAMBLE; break;
					case 'n': Modes.debug |= MODES_DEBUG_NET; break;
					case 'j': Modes.debug |= MODES_DEBUG_JS; break;
					default:
						  fprintf(stderr, "Unknown debugging flag: %c\n", *f);
						  exit(1);
						  break;
				}
				f++;
			}
		}
		else if (!strcmp(argv[j], "--stats")) {
			Modes.stats = 1;
		}
		else if (!strcmp(argv[j], "--snip") && more) {
			snipMode(atoi(argv[++j]));
			exit(0);
		}
		else if (!strcmp(argv[j], "--help")) {
			showHelp();
			exit(0);
		}
		else {
			fprintf(stderr,
					"Unknown or not enough arguments for option '%s'.\n\n",
					argv[j]);
			showHelp();
			exit(1);
		}
	}

	/* Setup for SIGWINCH for handling lines */
	if (Modes.interactive == 1) signal(SIGWINCH, sigWinchCallback);

	/* Initialization */
	modesInit();
	if (Modes.net_only) {
		fprintf(stderr, "Net-only mode, no PlutoSDR device or file open.\n");
	}
	else if (Modes.filename == NULL) {
		modesInitPLUTOSDR();
	}
	else {
		if (Modes.filename[0] == '-' && Modes.filename[1] == '\0') {
			Modes.fd = STDIN_FILENO;
		}
		else if ((Modes.fd = open(Modes.filename, O_RDONLY)) == -1) {
			perror("Opening data file");
			exit(1);
		}
	}
	if (Modes.net) modesInitNet();

	/* If the user specifies --net-only, just run in order to serve network
	 * clients without reading data from the PlutoSDR device. */
	while (Modes.net_only) {
		backgroundTasks();
		modesWaitReadableClients(100);
	}

	/* Create the thread that will read the data from the device. */
	pthread_create(&Modes.reader_thread, NULL, readerThreadEntryPoint, NULL);

	pthread_mutex_lock(&Modes.data_mutex);
	while (1) {
		if (!Modes.data_ready) {
			pthread_cond_wait(&Modes.data_cond, &Modes.data_mutex);
			continue;
		}
		computeMagnitudeVector();

		/* Signal to the other thread that we processed the available data
		 * and we want more (useful for --ifile). */
		Modes.data_ready = 0;
		pthread_cond_signal(&Modes.data_cond);

		/* Process data after releasing the lock, so that the capturing
		 * thread can read data while we perform computationally expensive
		 * stuff * at the same time. (This should only be useful with very
		 * slow processors). */
		pthread_mutex_unlock(&Modes.data_mutex);
		detectModeS(Modes.magnitude, Modes.data_len / 2);
		backgroundTasks();
		pthread_mutex_lock(&Modes.data_mutex);
		if (Modes.exit) break;
	}

	/* If --ifile and --stats were given, print statistics. */
	if (Modes.stats && Modes.filename) {
		printf("%lld valid preambles\n", Modes.stat_valid_preamble);
		printf("%lld demodulated again after phase correction\n",
				Modes.stat_out_of_phase);
		printf("%lld demodulated with zero errors\n",
				Modes.stat_demodulated);
		printf("%lld with good crc\n", Modes.stat_goodcrc);
		printf("%lld with bad crc\n", Modes.stat_badcrc);
		printf("%lld errors corrected\n", Modes.stat_fixed);
		printf("%lld single bit errors\n", Modes.stat_single_bit_fix);
		printf("%lld two bits errors\n", Modes.stat_two_bits_fix);
		printf("%lld total usable messages\n",
				Modes.stat_goodcrc + Modes.stat_fixed);
	}
	printf("* Destroying buffers\n");
	if (Modes.rxbuf) { iio_buffer_destroy(Modes.rxbuf); }

	printf("* Disabling streaming channels\n");
	if (Modes.rx0_i) { iio_channel_disable(Modes.rx0_i); }
	if (Modes.rx0_q) { iio_channel_disable(Modes.rx0_q); }

	printf("* Destroying context\n");
	if (Modes.ctx) { iio_context_destroy(Modes.ctx); }

	return 0;
}