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dump1090/dump1090.c
antirez 69ae2491a5 New AP brute forcing algorithm. 
The old approach was to loop over a small circular buffer of recently
seen addresses recomputing the CRC every time: this prevented the use of
a big cache, and 20 entries was too small in case of high traffic and
big range antennas.

@prog on ##rtlsdr suggested to use an alternative algorithm where
instead we compute the CRC of the message, and xor it to obtain the
address, that is later checked in our list of recently seen addresses.
This is a lot better and allows for bigger tables in O(1) lookup time.

I used this idea to implement a larger 1024 elements table. Instead of
writing a proper hash table I used the fact we are just dealing with a
cache, so I just hash the ICAO addess and overwrite the old entry at
that idex with the address-timestamp pair, not caring about collisions.

The bigger table makes a huge difference:
In a test vector of 113 seconds recording with 76 simultaneous aircrafts
the new algorithm detected around 10k more messages (!).
2013-01-07 01:15:29 +01:00

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/* Mode1090, a Mode S messages decoder for RTLSDR devices.
*
* 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 <fcntl.h>
#include <ctype.h>
#include "rtl-sdr.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 999999 /* 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
#define MODES_DEBUG_DEMODERR 2
#define MODES_DEBUG_BADCRC 3
#define MODES_DEBUG_GOODCRC 4
#define MODES_DEBUG_NOPREAMBLE 5
/* 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
#define MODES_NOTUSED(V) ((void) V)
/* 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. */
time_t seen; /* Time at which the last packet was received. */
long messages; /* Number of Mode S messages received. */
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. */
/* RTLSDR */
int dev_index;
int gain;
int enable_agc;
rtlsdr_dev_t *dev;
int freq;
/* 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 interactive; /* Interactive mode */
int interactive_rows; /* Interactive mode: max number of rows */
int stats; /* Print stats at exit in --ifile mode. */
int onlyaddr; /* Print only ICAO addresses. */
/* 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;
} 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 */
/* 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; /* Odd or 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; /* E/W direction. */
int ew_velocity; /* E/W velocity. */
int ns_dir; /* N/S direction. */
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);
void interactiveReceiveData(struct modesMessage *mm);
/* ============================= 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_MAX_GAIN;
Modes.dev_index = 0;
Modes.enable_agc = 0;
Modes.freq = MODES_DEFAULT_FREQ;
Modes.filename = NULL;
Modes.fix_errors = 1;
Modes.check_crc = 1;
Modes.raw = 0;
Modes.onlyaddr = 0;
Modes.debug = 0;
Modes.interactive = 0;
Modes.interactive_rows = MODES_INTERACTIVE_ROWS;
}
void modesInit(void) {
int i, q;
pthread_mutex_init(&Modes.data_mutex,NULL);
pthread_cond_init(&Modes.data_cond,NULL);
Modes.data_len = MODES_DATA_LEN;
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(Modes.icao_cache));
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);
}
/* 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.exit = 0;
}
/* =============================== RTLSDR handling ========================== */
void modesInitRTLSDR(void) {
int j;
int device_count;
int ppm_error = 0;
char vendor[256], product[256], serial[256];
device_count = rtlsdr_get_device_count();
if (!device_count) {
fprintf(stderr, "No supported RTLSDR devices found.\n");
exit(1);
}
fprintf(stderr, "Found %d device(s):\n", device_count);
for (j = 0; j < device_count; j++) {
rtlsdr_get_device_usb_strings(j, vendor, product, serial);
fprintf(stderr, "%d: %s, %s, SN: %s %s\n", j, vendor, product, serial,
(j == Modes.dev_index) ? "(currently selected)" : "");
}
if (rtlsdr_open(&Modes.dev, Modes.dev_index) < 0) {
fprintf(stderr, "Error opening the RTLSDR device: %s\n",
strerror(errno));
exit(1);
}
/* Set gain, frequency, sample rate, and reset the device. */
rtlsdr_set_tuner_gain_mode(Modes.dev,
(Modes.gain == MODES_AUTO_GAIN) ? 0 : 1);
if (Modes.gain != MODES_AUTO_GAIN) {
if (Modes.gain == MODES_MAX_GAIN) {
/* Find the maximum gain available. */
int numgains;
int gains[100];
numgains = rtlsdr_get_tuner_gains(Modes.dev, gains);
Modes.gain = gains[numgains-1];
fprintf(stderr, "Max available gain is: %.2f\n", Modes.gain/10.0);
}
rtlsdr_set_tuner_gain(Modes.dev, Modes.gain);
fprintf(stderr, "Setting gain to: %.2f\n", Modes.gain/10.0);
} else {
fprintf(stderr, "Using automatic gain control.\n");
}
rtlsdr_set_freq_correction(Modes.dev, ppm_error);
if (Modes.enable_agc) rtlsdr_set_agc_mode(Modes.dev, 1);
rtlsdr_set_center_freq(Modes.dev, Modes.freq);
rtlsdr_set_sample_rate(Modes.dev, MODES_DEFAULT_RATE);
rtlsdr_reset_buffer(Modes.dev);
fprintf(stderr, "Gain reported by device: %.2f\n",
rtlsdr_get_tuner_gain(Modes.dev)/10.0);
}
/* 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 rtlsdrCallback(unsigned char *buf, uint32_t len, void *ctx) {
MODES_NOTUSED(ctx);
pthread_mutex_lock(&Modes.data_mutex);
if (len > Modes.data_len) len = Modes.data_len;
memcpy(Modes.data, 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;
}
toread = Modes.data_len;
p = Modes.data;
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) {
rtlsdr_read_async(Modes.dev, rtlsdrCallback, NULL,
MODES_ASYNC_BUF_NUMBER,
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 5 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]);
}
}
/* 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
*/
void dumpRawMessage(char *descr, unsigned char *msg,
uint16_t *m, uint32_t offset)
{
int j;
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("\n");
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;
}
/* 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.
*
* On success the input buffer is modified to remove the xored checksum
* from the packet, so that the last three bytes will contain the
* plain ICAO address.
*
* If the function successfully recovers a message with a correct checksum
* it returns 1. Otherwise 0 is returned. */
int bruteForceAP(unsigned char *msg, int msgbits) {
unsigned char aux[MODES_LONG_MSG_BITS/8];
int msgtype = msg[0]>>3;
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)) {
msg[lastbyte] = aux[lastbyte];
msg[lastbyte-1] = aux[lastbyte-1];
msg[lastbyte-2] = aux[lastbyte-2];
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;
}
}
/* 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;
mm->identity = (msg[2]&31 << 8) | msg[3]; /* 13 bits identity. */
/* 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 (mm->msgtype != 11 && mm->msgtype != 17) {
/* Return to the caller now if we can't resolve the API field and
* we need to check the checksum. */
if (bruteForceAP(msg,mm->msgbits)) {
/* We recovered the message!
* Populate the AA fields with the right information. */
mm->aa3 = msg[mm->msgbits/8-1];
mm->aa2 = msg[mm->msgbits/8-2];
mm->aa1 = msg[mm->msgbits/8-3];
mm->crcok = 1;
} else {
mm->crcok = 0;
}
}
/* 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) >> 5;
mm->vert_rate = ((msg[8]&7) << 6) | ((msg[9]&0xfc) >> 2);
mm->velocity = sqrt(mm->ns_velocity*mm->ns_velocity+
mm->ew_velocity*mm->ew_velocity);
} 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));
}
}
}
}
/* 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) 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 : %o (octal)\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];
}
}
/* 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];
uint32_t j;
/* 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, i, errors;
/* 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. */
high = (m[j]+m[j+2]+m[j+7]+m[j+9])/4;
if (m[j+3] >= high ||
m[j+4] >= high ||
m[j+5] >= high ||
m[j+6] >= 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 10-15 must be low, as it is the
* space between the preamble and real data. */
if (m[j+10] >= high ||
m[j+11] >= high ||
m[j+12] >= high ||
m[j+13] >= high ||
m[j+14] >= high ||
m[j+15] >= 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++;
/* 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];
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;
}
}
/* 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? */
int 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) 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) {
struct modesMessage mm;
/* Decode the received message and update statistics */
decodeModesMessage(&mm,msg);
Modes.stat_demodulated++;
if (mm.errorbit == -1) {
if (mm.crcok)
Modes.stat_goodcrc++;
else
Modes.stat_badcrc++;
} else {
Modes.stat_badcrc++;
Modes.stat_fixed++;
}
/* Output debug mode info if needed. */
if (Modes.debug == MODES_DEBUG_DEMOD)
dumpRawMessage("Demodulated with 0 errors", msg, m, j);
else if (Modes.debug == MODES_DEBUG_BADCRC && !mm.crcok)
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);
/* Pass data to the next layer */
if (!Modes.stats && (Modes.check_crc == 0 || mm.crcok)) {
if (Modes.interactive) {
interactiveReceiveData(&mm);
} else {
displayModesMessage(&mm);
if (!Modes.raw && !Modes.onlyaddr) printf("\n");
}
}
/* Skip this message if we are sure it's fine. */
if (mm.crcok) j += (MODES_PREAMBLE_US+(msglen*8))*2;
} else {
if (Modes.debug == MODES_DEBUG_DEMODERR) {
printf("The following message has %d demod errors\n", errors);
dumpRawMessage("Demodulated with errors", msg, m, j);
}
}
}
}
/* ========================= 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->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;
}
/* Receive new messages and populate the interactive mode with more info. */
void interactiveReceiveData(struct modesMessage *mm) {
uint32_t addr;
struct aircraft *a, *aux;
if (Modes.check_crc && mm->crcok == 0) return;
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 (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;
} else if (mm->metype == 19) {
if (mm->mesub == 1 || mm->mesub == 2) {
a->speed = mm->velocity;
}
}
}
}
/* 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 Messages Seen %s\n",
progress);
printf("----------------------------------------------------\n");
while(a && count < Modes.interactive_rows) {
printf("%-6s %-8s %-9d %-9d %-9ld %d sec ago\n",
a->hexaddr, a->flight, a->altitude, a->speed, a->messages,
(int)(now - a->seen));
a = a->next;
count++;
}
}
/* ============================== 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);
}
}
/* ================================ Main ==================================== */
void showHelp(void) {
printf(
"--device-index <index> Select RTL device (default: 0).\n"
"--gain <db> Set gain (default: max gain. Use -100 for auto-gain).\n"
"--enable-agc <db> Enable the Automatic Gain Control (default: off).\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"
"--raw Show only messages hex values.\n"
"--no-fix Disable single-bits error correction using CRC.\n"
"--no-crc-check Disable messages with broken CRC (discouraged).\n"
"--stats With --ifile print stats at exit. No other output.\n"
"--onlyaddr Show only ICAO addresses (testing purposes).\n"
"--snip <level> Strip IQ file removing samples < level.\n"
"--debug <level> Debug mode, see README for more information.\n"
"--help Show this help.\n"
);
}
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])*10; /* Gain is in tens of DBs */
} else if (!strcmp(argv[j],"--enable-agc")) {
Modes.enable_agc++;
} 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],"--onlyaddr")) {
Modes.onlyaddr = 1;
} 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],"--debug") && more) {
Modes.debug = atoi(argv[++j]);
} 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);
}
}
modesInit();
if (Modes.filename == NULL) {
modesInitRTLSDR();
} 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);
}
}
/* 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);
/* Refresh screen when in interactive mode. */
if (Modes.interactive &&
(mstime() - Modes.interactive_last_update) >
MODES_INTERACTIVE_REFRESH_TIME)
{
interactiveShowData();
Modes.interactive_last_update = mstime();
}
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 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 single bit errors corrected\n", Modes.stat_fixed);
}
rtlsdr_close(Modes.dev);
return 0;
}
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