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// Part of dump1090, a Mode S message decoder for RTLSDR devices.
//
// mode_s.c: Mode S message decoding.
//
// Copyright (c) 2014-2016 Oliver Jowett <oliver@mutability.co.uk>
//
// This file is free software: you may copy, redistribute and/or modify it
// under the terms of the GNU General Public License as published by the
// Free Software Foundation, either version 2 of the License, or (at your
// option) any later version.
//
// This file is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
// This file incorporates work covered by the following copyright and
// permission notice:
//
// 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 "dump1090.h"
/* for PRIX64 */
#include <inttypes.h>
//
// ===================== Mode S detection and decoding ===================
//
//
//
/* A timestamp that indicates the data is synthetic, created from a
* multilateration result
*/
#define MAGIC_MLAT_TIMESTAMP 0xFF004D4C4154ULL
//=========================================================================
//
// Given the Downlink Format (DF) of the message, return the message length in bits.
//
// All known DF's 16 or greater are long. All known DF's 15 or less are short.
// There are lots of unused codes in both category, so we can assume ICAO will stick to
// these rules, meaning that the most significant bit of the DF indicates the length.
//
int modesMessageLenByType(int type) {
return (type & 0x10) ? MODES_LONG_MSG_BITS : MODES_SHORT_MSG_BITS ;
}
//
//=========================================================================
//
// In the squawk (identity) field bits are interleaved as follows in
// (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 hex
// number tha happens to represent the four octal numbers.
//
// For more info: http://en.wikipedia.org/wiki/Gillham_code
//
static int decodeID13Field(int ID13Field) {
int hexGillham = 0;
if (ID13Field & 0x1000) {hexGillham |= 0x0010;} // Bit 12 = C1
if (ID13Field & 0x0800) {hexGillham |= 0x1000;} // Bit 11 = A1
if (ID13Field & 0x0400) {hexGillham |= 0x0020;} // Bit 10 = C2
if (ID13Field & 0x0200) {hexGillham |= 0x2000;} // Bit 9 = A2
if (ID13Field & 0x0100) {hexGillham |= 0x0040;} // Bit 8 = C4
if (ID13Field & 0x0080) {hexGillham |= 0x4000;} // Bit 7 = A4
//if (ID13Field & 0x0040) {hexGillham |= 0x0800;} // Bit 6 = X or M
if (ID13Field & 0x0020) {hexGillham |= 0x0100;} // Bit 5 = B1
if (ID13Field & 0x0010) {hexGillham |= 0x0001;} // Bit 4 = D1 or Q
if (ID13Field & 0x0008) {hexGillham |= 0x0200;} // Bit 3 = B2
if (ID13Field & 0x0004) {hexGillham |= 0x0002;} // Bit 2 = D2
if (ID13Field & 0x0002) {hexGillham |= 0x0400;} // Bit 1 = B4
if (ID13Field & 0x0001) {hexGillham |= 0x0004;} // Bit 0 = D4
return (hexGillham);
}
//
//=========================================================================
//
// Decode the 13 bit AC altitude field (in DF 20 and others).
// Returns the altitude, and set 'unit' to either UNIT_METERS or UNIT_FEET.
//
static int decodeAC13Field(int AC13Field, altitude_unit_t *unit) {
int m_bit = AC13Field & 0x0040; // set = meters, clear = feet
int q_bit = AC13Field & 0x0010; // set = 25 ft encoding, clear = Gillham Mode C encoding
if (!m_bit) {
*unit = UNIT_FEET;
if (q_bit) {
// N is the 11 bit integer resulting from the removal of bit Q and M
int n = ((AC13Field & 0x1F80) >> 2) |
((AC13Field & 0x0020) >> 1) |
(AC13Field & 0x000F);
// The final altitude is resulting number multiplied by 25, minus 1000.
return ((n * 25) - 1000);
} else {
// N is an 11 bit Gillham coded altitude
int n = modeAToModeC(decodeID13Field(AC13Field));
if (n < -12) {
return INVALID_ALTITUDE;
}
return (100 * n);
}
} else {
*unit = UNIT_METERS;
// TODO: Implement altitude when meter unit is selected
return INVALID_ALTITUDE;
}
}
//
//=========================================================================
//
// Decode the 12 bit AC altitude field (in DF 17 and others).
//
static int decodeAC12Field(int AC12Field, altitude_unit_t *unit) {
int q_bit = AC12Field & 0x10; // Bit 48 = Q
*unit = UNIT_FEET;
if (q_bit) {
/// N is the 11 bit integer resulting from the removal of bit Q at bit 4
int n = ((AC12Field & 0x0FE0) >> 1) |
(AC12Field & 0x000F);
// The final altitude is the resulting number multiplied by 25, minus 1000.
return ((n * 25) - 1000);
} else {
// Make N a 13 bit Gillham coded altitude by inserting M=0 at bit 6
int n = ((AC12Field & 0x0FC0) << 1) |
(AC12Field & 0x003F);
n = modeAToModeC(decodeID13Field(n));
if (n < -12) {
return INVALID_ALTITUDE;
}
return (100 * n);
}
}
//
//=========================================================================
//
// Decode the 7 bit ground movement field PWL exponential style scale (ADS-B v2)
//
static float decodeMovementFieldV2(unsigned movement) {
// Note : movement codes 0,125,126,127 are all invalid, but they are
// trapped for before this function is called.
// Each movement value is a range of speeds;
// we return the midpoint of the range (rounded to the nearest integer)
if (movement >= 125) return 0; // invalid
else if (movement == 124) return 180; // gs > 175kt, pick a value..
else if (movement >= 109) return 100 + (movement - 109 + 0.5) * 5; // 100 < gs <= 175 in 5kt steps
else if (movement >= 94) return 70 + (movement - 94 + 0.5) * 2; // 70 < gs <= 100 in 2kt steps
else if (movement >= 39) return 15 + (movement - 39 + 0.5) * 1; // 15 < gs <= 70 in 1kt steps
else if (movement >= 13) return 2 + (movement - 13 + 0.5) * 0.50; // 2 < gs <= 15 in 0.5kt steps
else if (movement >= 9) return 1 + (movement - 9 + 0.5) * 0.25; // 1 < gs <= 2 in 0.25kt steps
else if (movement >= 3) return 0.125 + (movement - 3 + 0.5) * 0.875 / 6; // 0.125 < gs <= 1 in 0.875/6 kt step
else if (movement >= 2) return 0.125 / 2; // 0 < gs <= 0.125
// 1: stopped, gs = 0
// 0: no data
else return 0;
}
//
//=========================================================================
//
// Decode the 7 bit ground movement field PWL exponential style scale (ADS-B v0)
//
static float decodeMovementFieldV0(unsigned movement) {
// Note : movement codes 0,125,126,127 are all invalid, but they are
// trapped for before this function is called.
// Each movement value is a range of speeds;
// we return the midpoint of the range
if (movement >= 125) return 0; // invalid
else if (movement == 124) return 180; // gs >= 175kt, pick a value..
else if (movement >= 109) return 100 + (movement - 109 + 0.5) * 5; // 100 < gs <= 175 in 5kt steps
else if (movement >= 94) return 70 + (movement - 94 + 0.5) * 2; // 70 < gs <= 100 in 2kt steps
else if (movement >= 39) return 15 + (movement - 39 + 0.5) * 1; // 15 < gs <= 70 in 1kt steps
else if (movement >= 13) return 2 + (movement - 13 + 0.5) * 0.50; // 2 < gs <= 15 in 0.5kt steps
else if (movement >= 9) return 1 + (movement - 9 + 0.5) * 0.25; // 1 < gs <= 2 in 0.25kt steps
else if (movement >= 2) return 0.125 + (movement - 2 + 0.5) * 0.125; // 0.125 < gs <= 1 in 0.125kt step
// 1: stopped, gs < 0.125kt
// 0: no data
else return 0;
}
// Correct a decoded native-endian Address Announced field
// (from bits 8-31) if it is affected by the given error
// syndrome. Updates *addr and returns >0 if changed, 0 if
// it was unaffected.
static int correct_aa_field(uint32_t *addr, struct errorinfo *ei)
{
int i;
int addr_errors = 0;
if (!ei)
return 0;
for (i = 0; i < ei->errors; ++i) {
if (ei->bit[i] >= 8 && ei->bit[i] <= 31) {
*addr ^= 1 << (31 - ei->bit[i]);
++addr_errors;
}
}
return addr_errors;
}
// Score how plausible this ModeS message looks.
// The more positive, the more reliable the message is
// 1000: DF 0/4/5/16/24 with a CRC-derived address matching a known aircraft
// 1800: DF17/18 with good CRC and an address matching a known aircraft
// 1400: DF17/18 with good CRC and an address not matching a known aircraft
// 900: DF17/18 with 1-bit error and an address matching a known aircraft
// 700: DF17/18 with 1-bit error and an address not matching a known aircraft
// 450: DF17/18 with 2-bit error and an address matching a known aircraft
// 350: DF17/18 with 2-bit error and an address not matching a known aircraft
// 1600: DF11 with IID==0, good CRC and an address matching a known aircraft
// 800: DF11 with IID==0, 1-bit error and an address matching a known aircraft
// 750: DF11 with IID==0, good CRC and an address not matching a known aircraft
// 375: DF11 with IID==0, 1-bit error and an address not matching a known aircraft
// 1000: DF11 with IID!=0, good CRC and an address matching a known aircraft
// 500: DF11 with IID!=0, 1-bit error and an address matching a known aircraft
// 1000: DF20/21 with a CRC-derived address matching a known aircraft
// 500: DF20/21 with a CRC-derived address matching a known aircraft (bottom 16 bits only - overlay control in use)
// -1: message might be valid, but we couldn't validate the CRC against a known ICAO
// -2: bad message or unrepairable CRC error
static unsigned char all_zeros[14] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
int scoreModesMessage(unsigned char *msg, int validbits)
{
int msgtype, msgbits, crc, iid;
uint32_t addr;
struct errorinfo *ei;
if (validbits < 56)
return -2;
msgtype = getbits(msg, 1, 5); // Downlink Format
msgbits = modesMessageLenByType(msgtype);
if (validbits < msgbits)
return -2;
if (!memcmp(all_zeros, msg, msgbits/8))
return -2;
crc = modesChecksum(msg, msgbits);
switch (msgtype) {
case 0: // short air-air surveillance
case 4: // surveillance, altitude reply
case 5: // surveillance, altitude reply
case 16: // long air-air surveillance
case 24: // Comm-D (ELM)
case 25: // Comm-D (ELM)
case 26: // Comm-D (ELM)
case 27: // Comm-D (ELM)
case 28: // Comm-D (ELM)
case 29: // Comm-D (ELM)
case 30: // Comm-D (ELM)
case 31: // Comm-D (ELM)
return icaoFilterTest(crc) ? 1000 : -1;
case 11: // All-call reply
iid = crc & 0x7f;
crc = crc & 0xffff80;
addr = getbits(msg, 9, 32);
ei = modesChecksumDiagnose(crc, msgbits);
if (!ei)
return -2; // can't correct errors
// see crc.c comments: we do not attempt to fix
// more than single-bit errors, as two-bit
// errors are ambiguous in DF11.
if (ei->errors > 1)
return -2; // can't correct errors
// fix any errors in the address field
correct_aa_field(&addr, ei);
// validate address
if (iid == 0) {
if (icaoFilterTest(addr))
return 1600 / (ei->errors + 1);
else
return 750 / (ei->errors + 1);
} else {
if (icaoFilterTest(addr))
return 1000 / (ei->errors + 1);
else
return -1;
}
case 17: // Extended squitter
case 18: // Extended squitter/non-transponder
ei = modesChecksumDiagnose(crc, msgbits);
if (!ei)
return -2; // can't correct errors
// fix any errors in the address field
addr = getbits(msg, 9, 32);
correct_aa_field(&addr, ei);
if (icaoFilterTest(addr))
return 1800 / (ei->errors+1);
else
return 1400 / (ei->errors+1);
case 20: // Comm-B, altitude reply
case 21: // Comm-B, identity reply
if (icaoFilterTest(crc))
return 1000; // Address/Parity
#if 0
// This doesn't seem useful, as we mistake a lot of CRC errors
// for overlay control
if (icaoFilterTestFuzzy(crc))
return 500; // Data/Parity
#endif
return -2;
default:
// unknown message type
return -2;
}
}
//
//=========================================================================
//
// Decode a raw Mode S message demodulated as a stream of bytes by detectModeS(),
// and split it into fields populating a modesMessage structure.
//
static void decodeExtendedSquitter(struct modesMessage *mm);
char ais_charset[64] = "@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_ !\"#$%&'()*+,-./0123456789:;<=>?";
// return 0 if all OK
// -1: message might be valid, but we couldn't validate the CRC against a known ICAO
// -2: bad message or unrepairable CRC error
int decodeModesMessage(struct modesMessage *mm, unsigned char *msg)
{
// Work on our local copy.
memcpy(mm->msg, msg, MODES_LONG_MSG_BYTES);
if (Modes.net_verbatim) {
// Preserve the original uncorrected copy for later forwarding
memcpy(mm->verbatim, msg, MODES_LONG_MSG_BYTES);
}
msg = mm->msg;
// don't accept all-zeros messages
if (!memcmp(all_zeros, msg, 7))
return -2;
// Get the message type ASAP as other operations depend on this
mm->msgtype = getbits(msg, 1, 5); // Downlink Format
mm->msgbits = modesMessageLenByType(mm->msgtype);
mm->crc = modesChecksum(msg, mm->msgbits);
mm->correctedbits = 0;
mm->addr = 0;
// Do checksum work and set fields that depend on the CRC
switch (mm->msgtype) {
case 0: // short air-air surveillance
case 4: // surveillance, altitude reply
case 5: // surveillance, altitude reply
case 16: // long air-air surveillance
case 24: // Comm-D (ELM)
case 25: // Comm-D (ELM)
case 26: // Comm-D (ELM)
case 27: // Comm-D (ELM)
case 28: // Comm-D (ELM)
case 29: // Comm-D (ELM)
case 30: // Comm-D (ELM)
case 31: // Comm-D (ELM)
// These message types use Address/Parity, i.e. our CRC syndrome is the sender's ICAO address.
// We can't tell if the CRC is correct or not as we don't know the correct address.
// Accept the message if it appears to be from a previously-seen aircraft
if (!icaoFilterTest(mm->crc)) {
return -1;
}
mm->source = SOURCE_MODE_S;
mm->addr = mm->crc;
break;
case 11: // All-call reply
// This message type uses Parity/Interrogator, i.e. our CRC syndrome is CL + IC from the uplink message
// which we can't see. So we don't know if the CRC is correct or not.
//
// however! CL + IC only occupy the lower 7 bits of the CRC. So if we ignore those bits when testing
// the CRC we can still try to detect/correct errors.
mm->IID = mm->crc & 0x7f;
if (mm->crc & 0xffff80) {
int addr;
struct errorinfo *ei = modesChecksumDiagnose(mm->crc & 0xffff80, mm->msgbits);
if (!ei) {
return -2; // couldn't fix it
}
// see crc.c comments: we do not attempt to fix
// more than single-bit errors, as two-bit
// errors are ambiguous in DF11.
if (ei->errors > 1)
return -2; // can't correct errors
mm->correctedbits = ei->errors;
modesChecksumFix(msg, ei);
// check whether the corrected message looks sensible
// we are conservative here: only accept corrected messages that
// match an existing aircraft.
addr = getbits(msg, 9, 32);
if (!icaoFilterTest(addr)) {
return -1;
}
}
mm->source = SOURCE_MODE_S_CHECKED;
break;
case 17: // Extended squitter
case 18: { // Extended squitter/non-transponder
struct errorinfo *ei;
int addr1, addr2;
// These message types use Parity/Interrogator, but are specified to set II=0
if (mm->crc != 0) {
ei = modesChecksumDiagnose(mm->crc, mm->msgbits);
if (!ei) {
return -2; // couldn't fix it
}
addr1 = getbits(msg, 9, 32);
mm->correctedbits = ei->errors;
modesChecksumFix(msg, ei);
addr2 = getbits(msg, 9, 32);
// we are conservative here: only accept corrected messages that
// match an existing aircraft.
if (addr1 != addr2 && !icaoFilterTest(addr2)) {
return -1;
}
}
mm->source = SOURCE_ADSB; // TIS-B decoding will override this if needed
break;
}
case 20: // Comm-B, altitude reply
case 21: // Comm-B, identity reply
// These message types either use Address/Parity (see DF0 etc)
// or Data Parity where the requested BDS is also xored into the top byte.
// So not only do we not know whether the CRC is right, we also don't know if
// the ICAO is right! Ow.
// Try an exact match
if (icaoFilterTest(mm->crc)) {
// OK.
mm->source = SOURCE_MODE_S;
mm->addr = mm->crc;
break;
}
// BDS / overlay control just doesn't work out.
return -1; // no good
default:
// All other message types, we don't know how to handle their CRCs, give up
return -2;
}
// decode the bulk of the message
// AA (Address announced)
if (mm->msgtype == 11 || mm->msgtype == 17 || mm->msgtype == 18) {
mm->AA = mm->addr = getbits(msg, 9, 32);
}
// AC (Altitude Code)
if (mm->msgtype == 0 || mm->msgtype == 4 || mm->msgtype == 16 || mm->msgtype == 20) {
mm->AC = getbits(msg, 20, 32);
if (mm->AC) { // Only attempt to decode if a valid (non zero) altitude is present
mm->altitude_baro = decodeAC13Field(mm->AC, &mm->altitude_baro_unit);
if (mm->altitude_baro != INVALID_ALTITUDE)
mm->altitude_baro_valid = 1;
}
}
// AF (DF19 Application Field) not decoded
// CA (Capability)
if (mm->msgtype == 11 || mm->msgtype == 17) {
mm->CA = getbits(msg, 6, 8);
switch (mm->CA) {
case 0:
mm->airground = AG_UNCERTAIN;
break;
case 4:
mm->airground = AG_GROUND;
break;
case 5:
mm->airground = AG_AIRBORNE;
break;
case 6:
mm->airground = AG_UNCERTAIN;
break;
case 7:
mm->airground = AG_UNCERTAIN;
break;
}
}
// CC (Cross-link capability)
if (mm->msgtype == 0) {
mm->CC = getbit(msg, 7);
}
// CF (Control field)
if (mm->msgtype == 18) {
mm->CF = getbits(msg, 5, 8);
}
// DR (Downlink Request)
if (mm->msgtype == 4 || mm->msgtype == 5 || mm->msgtype == 20 || mm->msgtype == 21) {
mm->DR = getbits(msg, 9, 13);
}
// FS (Flight Status)
if (mm->msgtype == 4 || mm->msgtype == 5 || mm->msgtype == 20 || mm->msgtype == 21) {
mm->FS = getbits(msg, 6, 8);
mm->alert_valid = 1;
mm->spi_valid = 1;
switch (mm->FS) {
case 0:
mm->airground = AG_UNCERTAIN;
break;
case 1:
mm->airground = AG_GROUND;
break;
case 2:
mm->airground = AG_UNCERTAIN;
mm->alert = 1;
break;
case 3:
mm->airground = AG_GROUND;
mm->alert = 1;
break;
case 4:
mm->airground = AG_UNCERTAIN;
mm->alert = 1;
mm->spi = 1;
break;
case 5:
mm->airground = AG_UNCERTAIN;
mm->spi = 1;
break;
default:
mm->spi_valid = 0;
mm->alert_valid = 0;
break;
}
}
// ID (Identity)
if (mm->msgtype == 5 || mm->msgtype == 21) {
// Gillham encoded Squawk
mm->ID = getbits(msg, 20, 32);
if (mm->ID) {
mm->squawk = decodeID13Field(mm->ID);
mm->squawk_valid = 1;
}
}
// KE (Control, ELM)
if (mm->msgtype >= 24 && mm->msgtype <= 31) {
mm->KE = getbit(msg, 4);
}
// MB (messsage, Comm-B)
if (mm->msgtype == 20 || mm->msgtype == 21) {
memcpy(mm->MB, &msg[4], 7);
decodeCommB(mm);
}
// MD (message, Comm-D)
if (mm->msgtype >= 24 && mm->msgtype <= 31) {
memcpy(mm->MD, &msg[1], 10);
}
// ME (message, extended squitter)
if (mm->msgtype == 17 || mm->msgtype == 18) {
memcpy(mm->ME, &msg[4], 7);
decodeExtendedSquitter(mm);
}
// MV (message, ACAS)
if (mm->msgtype == 16) {
memcpy(mm->MV, &msg[4], 7);
}
// ND (number of D-segment, Comm-D)
if (mm->msgtype >= 24 && mm->msgtype <= 31) {
mm->ND = getbits(msg, 5, 8);
}
// RI (Reply information, ACAS)
if (mm->msgtype == 0 || mm->msgtype == 16) {
mm->RI = getbits(msg, 14, 17);
}
// SL (Sensitivity level, ACAS)
if (mm->msgtype == 0 || mm->msgtype == 16) {
mm->SL = getbits(msg, 9, 11);
}
// UM (Utility Message)
if (mm->msgtype == 4 || mm->msgtype == 5 || mm->msgtype == 20 || mm->msgtype == 21) {
mm->UM = getbits(msg, 14, 19);
}
// VS (Vertical Status)
if (mm->msgtype == 0 || mm->msgtype == 16) {
mm->VS = getbit(msg, 6);
if (mm->VS)
mm->airground = AG_GROUND;
else
mm->airground = AG_UNCERTAIN;
}
if (!mm->correctedbits && (mm->msgtype == 17 || mm->msgtype == 18 || (mm->msgtype == 11 && mm->IID == 0))) {
// No CRC errors seen, and either it was an DF17/18 extended squitter
// or a DF11 acquisition squitter with II = 0. We probably have the right address.
// We wait until here to do this as we may have needed to decode an ES to note
// the type of address in DF18 messages.
// NB this is the only place that adds addresses!
icaoFilterAdd(mm->addr);
}
// MLAT overrides all other sources
if (mm->remote && mm->timestampMsg == MAGIC_MLAT_TIMESTAMP)
mm->source = SOURCE_MLAT;
// all done
return 0;
}
static void decodeESIdentAndCategory(struct modesMessage *mm)
{
// Aircraft Identification and Category
unsigned char *me = mm->ME;
mm->mesub = getbits(me, 6, 8);
mm->callsign[0] = ais_charset[getbits(me, 9, 14)];
mm->callsign[1] = ais_charset[getbits(me, 15, 20)];
mm->callsign[2] = ais_charset[getbits(me, 21, 26)];
mm->callsign[3] = ais_charset[getbits(me, 27, 32)];
mm->callsign[4] = ais_charset[getbits(me, 33, 38)];
mm->callsign[5] = ais_charset[getbits(me, 39, 44)];
mm->callsign[6] = ais_charset[getbits(me, 45, 50)];
mm->callsign[7] = ais_charset[getbits(me, 51, 56)];
mm->callsign[8] = 0;
// A common failure mode seems to be to intermittently send
// all zeros. Catch that here.
mm->callsign_valid = (strcmp(mm->callsign, "@@@@@@@@") != 0);
mm->category = ((0x0E - mm->metype) << 4) | mm->mesub;
mm->category_valid = 1;
}
// Handle setting a non-ICAO address
static void setIMF(struct modesMessage *mm)
{
mm->addr |= MODES_NON_ICAO_ADDRESS;
switch (mm->addrtype) {
case ADDR_ADSB_ICAO:
case ADDR_ADSB_ICAO_NT:
// Shouldn't happen, but let's try to handle it
mm->addrtype = ADDR_ADSB_OTHER;
break;
case ADDR_TISB_ICAO:
mm->addrtype = ADDR_TISB_TRACKFILE;
break;
case ADDR_ADSR_ICAO:
mm->addrtype = ADDR_ADSR_OTHER;
break;
default:
// Nothing.
break;
}
}
static void decodeESAirborneVelocity(struct modesMessage *mm, int check_imf)
{
// Airborne Velocity Message
unsigned char *me = mm->ME;
// 1-5: ME type
// 6-8: ME subtype
mm->mesub = getbits(me, 6, 8);
if (mm->mesub < 1 || mm->mesub > 4)
return;
// 9: IMF or Intent Change
if (check_imf && getbit(me, 9))
setIMF(mm);
// 10: reserved
// 11-13: NACv (NUCr in v0, maps directly to NACv in v2)
mm->accuracy.nac_v_valid = 1;
mm->accuracy.nac_v = getbits(me, 11, 13);
// 14-35: speed/velocity depending on subtype
switch (mm->mesub) {
case 1: case 2:
{
// 14: E/W direction
// 15-24: E/W speed
// 25: N/S direction
// 26-35: N/S speed
unsigned ew_raw = getbits(me, 15, 24);
unsigned ns_raw = getbits(me, 26, 35);
if (ew_raw && ns_raw) {
int ew_vel = (ew_raw - 1) * (getbit(me, 14) ? -1 : 1) * ((mm->mesub == 2) ? 4 : 1);
int ns_vel = (ns_raw - 1) * (getbit(me, 25) ? -1 : 1) * ((mm->mesub == 2) ? 4 : 1);
// Compute velocity and angle from the two speed components
mm->gs.v0 = mm->gs.v2 = mm->gs.selected = sqrtf((ns_vel * ns_vel) + (ew_vel * ew_vel) + 0.5);
mm->gs_valid = 1;
if (mm->gs.selected > 0) {
float ground_track = atan2(ew_vel, ns_vel) * 180.0 / M_PI;
// We don't want negative values but a 0-360 scale
if (ground_track < 0)
ground_track += 360;
mm->heading = ground_track;
mm->heading_type = HEADING_GROUND_TRACK;
mm->heading_valid = 1;
}
}
break;
}
case 3: case 4:
{
// 14: heading status
// 15-24: heading
if (getbit(me, 14)) {
mm->heading_valid = 1;
mm->heading = getbits(me, 15, 24) * 360.0 / 1024.0;
mm->heading_type = HEADING_MAGNETIC_OR_TRUE;
}
// 25: airspeed type
// 26-35: airspeed
unsigned airspeed = getbits(me, 26, 35);
if (airspeed) {
unsigned speed = (airspeed - 1) * (mm->mesub == 4 ? 4 : 1);
if (getbit(me, 25)) {
mm->tas_valid = 1;
mm->tas = speed;
} else {
mm->ias_valid = 1;
mm->ias = speed;
}
}
break;
}
}
// 36: vert rate source
// 37: vert rate sign
// 38-46: vert rate magnitude
unsigned vert_rate = getbits(me, 38, 46);
unsigned vert_rate_is_baro = getbit(me, 36);
if (vert_rate) {
int rate = (vert_rate - 1) * (getbit(me, 37) ? -64 : 64);
if (vert_rate_is_baro) {
mm->baro_rate = rate;
mm->baro_rate_valid = 1;
} else {
mm->geom_rate = rate;
mm->geom_rate_valid = 1;
}
}
// 47-48: reserved
// 49: baro/geom delta sign
// 50-56: baro/geom delta magnitude
unsigned raw_delta = getbits(me, 50, 56);
if (raw_delta) {
mm->geom_delta_valid = 1;
mm->geom_delta = (raw_delta - 1) * (getbit(me, 49) ? -25 : 25);
}
}
static void decodeESSurfacePosition(struct modesMessage *mm, int check_imf)
{
// Surface position and movement
unsigned char *me = mm->ME;
mm->airground = AG_GROUND; // definitely.
mm->cpr_valid = 1;
mm->cpr_type = CPR_SURFACE;
// 6-12: Movement
unsigned movement = getbits(me, 6, 12);
if (movement > 0 && movement < 125) {
mm->gs_valid = 1;
mm->gs.selected = mm->gs.v0 = decodeMovementFieldV0(movement); // assumed v0 until told otherwise
mm->gs.v2 = decodeMovementFieldV2(movement);
}
// 13: Heading/track status
// 14-20: Heading/track
if (getbit(me, 13)) {
mm->heading_valid = 1;
mm->heading = getbits(me, 14, 20) * 360.0 / 128.0;
mm->heading_type = HEADING_TRACK_OR_HEADING;
}
// 21: IMF or T flag
if (check_imf && getbit(me, 21))
setIMF(mm);
// 22: F flag (odd/even)
mm->cpr_odd = getbit(me, 22);
// 23-39: CPR encoded latitude
mm->cpr_lat = getbits(me, 23, 39);
// 40-56: CPR encoded longitude
mm->cpr_lon = getbits(me, 40, 56);
}
static void decodeESAirbornePosition(struct modesMessage *mm, int check_imf)
{
// Airborne position and altitude
unsigned char *me = mm->ME;
// 6-7: surveillance status
// 8: IMF or NIC supplement-B
if (check_imf) {
if (getbit(me, 8))
setIMF(mm);
} else {
// NIC-B (v2) or SAF (v0/v1)
mm->accuracy.nic_b_valid = 1;
mm->accuracy.nic_b = getbit(me, 8);
}
// 9-20: altitude
unsigned AC12Field = getbits(me, 9, 20);
if (mm->metype == 0) {
// no position information
} else {
// 21: T flag (UTC sync or not)
// 22: F flag (odd or even)
// 23-39: CPR encoded latitude
// 40-56: CPR encoded longitude
mm->cpr_lat = getbits(me, 23, 39);
mm->cpr_lon = getbits(me, 40, 56);
// Catch some common failure modes and don't mark them as valid
// (so they won't be used for positioning)
if (AC12Field == 0 && mm->cpr_lon == 0 && (mm->cpr_lat & 0x0fff) == 0 && mm->metype == 15) {
// Seen from at least:
// 400F3F (Eurocopter ECC155 B1) - Bristow Helicopters
// 4008F3 (BAE ATP) - Atlantic Airlines
// 400648 (BAE ATP) - Atlantic Airlines
// altitude == 0, longitude == 0, type == 15 and zeros in latitude LSB.
// Can alternate with valid reports having type == 14
Modes.stats_current.cpr_filtered++;
} else {
// Otherwise, assume it's valid.
mm->cpr_valid = 1;
mm->cpr_type = CPR_AIRBORNE;
mm->cpr_odd = getbit(me, 22);
}
}
if (AC12Field) {// Only attempt to decode if a valid (non zero) altitude is present
altitude_unit_t unit;
int alt = decodeAC12Field(AC12Field, &unit);
if (alt != INVALID_ALTITUDE) {
if (mm->metype == 20 || mm->metype == 21 || mm->metype == 22) {
mm->altitude_geom = alt;
mm->altitude_geom_unit = unit;
mm->altitude_geom_valid = 1;
} else {
mm->altitude_baro = alt;
mm->altitude_baro_unit = unit;
mm->altitude_baro_valid = 1;
}
}
}
}
static void decodeESTestMessage(struct modesMessage *mm)
{
unsigned char *me = mm->ME;
mm->mesub = getbits(me, 6, 8);
if (mm->mesub == 7) { // (see 1090-WP-15-20)
int ID13Field = getbits(me, 9, 21);
if (ID13Field) {
mm->squawk_valid = 1;
mm->squawk = decodeID13Field(ID13Field);
}
}
}
static void decodeESAircraftStatus(struct modesMessage *mm, int check_imf)
{
// Extended Squitter Aircraft Status
unsigned char *me = mm->ME;
mm->mesub = getbits(me, 6, 8);
if (mm->mesub == 1) { // Emergency status squawk field
mm->emergency_valid = 1;
mm->emergency = (emergency_t) getbits(me, 9, 11);
unsigned ID13Field = getbits(me, 12, 24);
if (ID13Field) {
mm->squawk_valid = 1;
mm->squawk = decodeID13Field(ID13Field);
}
if (check_imf && getbit(me, 56))
setIMF(mm);
}
}
static void decodeESTargetStatus(struct modesMessage *mm, int check_imf)
{
unsigned char *me = mm->ME;
mm->mesub = getbits(me, 6, 7); // an unusual message: only 2 bits of subtype
if (check_imf && getbit(me, 51))
setIMF(mm);
if (mm->mesub == 0 && getbit(me, 11) == 0) { // Target state and status, V1
// 8-9: vertical source
switch (getbits(me, 8, 9)) {
case 1:
mm->nav.altitude_source = NAV_ALT_MCP;
break;
case 2:
mm->nav.altitude_source = NAV_ALT_AIRCRAFT;
break;
case 3:
mm->nav.altitude_source = NAV_ALT_FMS;
break;
default:
// nothing
break;
}
// 10: target altitude type (ignored)
// 11: backward compatibility bit, always 0
// 12-13: target alt capabilities (ignored)
// 14-15: vertical mode
switch (getbits(me, 14, 15)) {
case 1: // "acquiring"
mm->nav.modes_valid = 1;
if (mm->nav.altitude_source == NAV_ALT_FMS) {
mm->nav.modes |= NAV_MODE_VNAV;
} else {
mm->nav.modes |= NAV_MODE_AUTOPILOT;
}
break;
case 2: // "maintaining"
mm->nav.modes_valid = 1;
if (mm->nav.altitude_source == NAV_ALT_FMS) {
mm->nav.modes |= NAV_MODE_VNAV;
} else if (mm->nav.altitude_source == NAV_ALT_AIRCRAFT) {
mm->nav.modes |= NAV_MODE_ALT_HOLD;
} else {
mm->nav.modes |= NAV_MODE_AUTOPILOT;
}
break;
default:
// nothing
break;
}
// 16-25: altitude
int alt = -1000 + 100 * getbits(me, 16, 25);
switch (mm->nav.altitude_source) {
case NAV_ALT_MCP:
mm->nav.mcp_altitude_valid = 1;
mm->nav.mcp_altitude = alt;
break;
case NAV_ALT_FMS:
mm->nav.fms_altitude_valid = 1;
mm->nav.fms_altitude = alt;
break;
default:
// nothing
break;
}
// 26-27: horizontal data source
unsigned h_source = getbits(me, 26, 27);
if (h_source != 0) {
// 28-36: target heading/track
mm->nav.heading_valid = 1;
mm->nav.heading = getbits(me, 28, 36);
// 37: track vs heading
if (getbit(me, 37)) {
mm->nav.heading_type = HEADING_GROUND_TRACK;
} else {
mm->nav.heading_type = HEADING_MAGNETIC_OR_TRUE;
}
}
// 38-39: horiontal mode
switch (getbits(me, 38, 39)) {
case 1: // acquiring
case 2: // maintaining
mm->nav.modes_valid = 1;
if (h_source == 3) { // FMS
mm->nav.modes |= NAV_MODE_LNAV;
} else {
mm->nav.modes |= NAV_MODE_AUTOPILOT;
}
break;
default:
// nothing
break;
}
// 40-43: NACp
mm->accuracy.nac_p_valid = 1;
mm->accuracy.nac_p = getbits(me, 40, 43);
// 44: NICbaro
mm->accuracy.nic_baro_valid = 1;
mm->accuracy.nic_baro = getbit(me, 44);
// 45-46: SIL
mm->accuracy.sil = getbits(me, 45, 46);
mm->accuracy.sil_type = SIL_UNKNOWN;
// 47-51: reserved
// 52-53: TCAS status
switch (getbits(me, 52, 53)) {
case 1:
mm->nav.modes_valid = 1;
// no tcas
break;
case 2:
case 3:
mm->nav.modes_valid = 1;
mm->nav.modes |= NAV_MODE_TCAS;
break;
case 0:
// assume TCAS if we had any other modes
// but don't enable modes just for this
mm->nav.modes |= NAV_MODE_TCAS;
break;
default:
// nothing
break;
}
// 54-56: emergency/priority
mm->emergency_valid = 1;
mm->emergency = (emergency_t) getbits(me, 54, 56);
} else if (mm->mesub == 1) { // Target state and status, V2
// 8: SIL
unsigned is_fms = getbit(me, 9);
unsigned alt_bits = getbits(me, 10, 20);
if (alt_bits != 0) {
if (is_fms) {
mm->nav.fms_altitude_valid = 1;
mm->nav.fms_altitude = (alt_bits - 1) * 32;
} else {
mm->nav.mcp_altitude_valid = 1;
mm->nav.mcp_altitude = (alt_bits - 1) * 32;
}
}
unsigned baro_bits = getbits(me, 21, 29);
if (baro_bits != 0) {
mm->nav.qnh_valid = 1;
mm->nav.qnh = 800.0 + (baro_bits - 1) * 0.8;
}
if (getbit(me, 30)) {
mm->nav.heading_valid = 1;
// two's complement -180..+180, which is conveniently
// also the same as unsigned 0..360
mm->nav.heading = getbits(me, 31, 39) * 180.0 / 256.0;
mm->nav.heading_type = HEADING_MAGNETIC_OR_TRUE;
}
// 40-43: NACp
mm->accuracy.nac_p_valid = 1;
mm->accuracy.nac_p = getbits(me, 40, 43);
// 44: NICbaro
mm->accuracy.nic_baro_valid = 1;
mm->accuracy.nic_baro = getbit(me, 44);
// 45-46: SIL
mm->accuracy.sil = getbits(me, 45, 46);
mm->accuracy.sil_type = SIL_UNKNOWN;
// 47: mode bits validity
if (getbit(me, 47)) {
// 48-54: mode bits
mm->nav.modes_valid = 1;
mm->nav.modes =
(getbit(me, 48) ? NAV_MODE_AUTOPILOT : 0) |
(getbit(me, 49) ? NAV_MODE_VNAV : 0) |
(getbit(me, 50) ? NAV_MODE_ALT_HOLD : 0) |
// 51: IMF
(getbit(me, 52) ? NAV_MODE_APPROACH : 0) |
(getbit(me, 53) ? NAV_MODE_TCAS : 0) |
(getbit(me, 54) ? NAV_MODE_LNAV : 0);
}
// 55-56 reserved
}
}
static void decodeESOperationalStatus(struct modesMessage *mm, int check_imf)
{
unsigned char *me = mm->ME;
mm->mesub = getbits(me, 6, 8);
// Aircraft Operational Status
if (check_imf && getbit(me, 56))
setIMF(mm);
if (mm->mesub == 0 || mm->mesub == 1) {
mm->opstatus.valid = 1;
mm->opstatus.version = getbits(me, 41, 43);
switch (mm->opstatus.version) {
case 0:
if (mm->mesub == 0 && getbits(me, 9, 10) == 0) {
mm->opstatus.cc_acas = !getbit(me, 12);
mm->opstatus.cc_cdti = getbit(me, 13);
}
break;
case 1:
if (getbits(me, 25, 26) == 0) {
mm->opstatus.om_acas_ra = getbit(me, 27);
mm->opstatus.om_ident = getbit(me, 28);
mm->opstatus.om_atc = getbit(me, 29);
}
if (mm->mesub == 0 && getbits(me, 9, 10) == 0 && getbits(me, 13, 14) == 0) {
// airborne
mm->opstatus.cc_acas = !getbit(me, 11);
mm->opstatus.cc_cdti = getbit(me, 12);
mm->opstatus.cc_arv = getbit(me, 15);
mm->opstatus.cc_ts = getbit(me, 16);
mm->opstatus.cc_tc = getbits(me, 17, 18);
} else if (mm->mesub == 1 && getbits(me, 9, 10) == 0 && getbits(me, 13, 14) == 0) {
// surface
mm->opstatus.cc_poa = getbit(me, 11);
mm->opstatus.cc_cdti = getbit(me, 12);
mm->opstatus.cc_b2_low = getbit(me, 15);
mm->opstatus.cc_lw_valid = 1;
mm->opstatus.cc_lw = getbits(me, 21, 24);
}
mm->accuracy.nic_a_valid = 1;
mm->accuracy.nic_a = getbit(me, 44);
mm->accuracy.nac_p_valid = 1;
mm->accuracy.nac_p = getbits(me, 45, 48);
mm->accuracy.sil_type = SIL_UNKNOWN;
mm->accuracy.sil = getbits(me, 51, 52);
mm->opstatus.hrd = getbit(me, 54) ? HEADING_MAGNETIC : HEADING_TRUE;
if (mm->mesub == 0) {
mm->accuracy.nic_baro_valid = 1;
mm->accuracy.nic_baro = getbit(me, 53);
} else {
mm->opstatus.tah = getbit(me, 53) ? HEADING_GROUND_TRACK : mm->opstatus.hrd;
}
break;
case 2:
if (getbits(me, 25, 26) == 0) {
mm->opstatus.om_acas_ra = getbit(me, 27);
mm->opstatus.om_ident = getbit(me, 28);
mm->opstatus.om_atc = getbit(me, 29);
mm->opstatus.om_saf = getbit(me, 30);
mm->accuracy.sda_valid = 1;
mm->accuracy.sda = getbits(me, 31, 32);
}
if (mm->mesub == 0 && getbits(me, 9, 10) == 0) {
// airborne
mm->opstatus.cc_acas = getbit(me, 11); // nb inverted sense versus v0/v1
mm->opstatus.cc_1090_in = getbit(me, 12);
mm->opstatus.cc_arv = getbit(me, 15);
mm->opstatus.cc_ts = getbit(me, 16);
mm->opstatus.cc_tc = getbits(me, 17, 18);
mm->opstatus.cc_uat_in = getbit(me, 19);
} else if (mm->mesub == 1 && getbits(me, 9, 10) == 0) {
// surface
mm->opstatus.cc_poa = getbit(me, 11);
mm->opstatus.cc_1090_in = getbit(me, 12);
mm->opstatus.cc_b2_low = getbit(me, 15);
mm->opstatus.cc_uat_in = getbit(me, 16);
mm->accuracy.nac_v_valid = 1;
mm->accuracy.nac_v = getbits(me, 17, 19);
mm->accuracy.nic_c_valid = 1;
mm->accuracy.nic_c = getbit(me, 20);
mm->opstatus.cc_lw_valid = 1;
mm->opstatus.cc_lw = getbits(me, 21, 24);
mm->opstatus.cc_antenna_offset = getbits(me, 33, 40);
}
mm->accuracy.nic_a_valid = 1;
mm->accuracy.nic_a = getbit(me, 44);
mm->accuracy.nac_p_valid = 1;
mm->accuracy.nac_p = getbits(me, 45, 48);
mm->accuracy.sil = getbits(me, 51, 52);
mm->accuracy.sil_type = getbit(me, 55) ? SIL_PER_SAMPLE : SIL_PER_HOUR;
mm->opstatus.hrd = getbit(me, 54) ? HEADING_MAGNETIC : HEADING_TRUE;
if (mm->mesub == 0) {
mm->accuracy.gva_valid = 1;
mm->accuracy.gva = getbits(me, 49, 50);
mm->accuracy.nic_baro_valid = 1;
mm->accuracy.nic_baro = getbit(me, 53);
} else {
mm->opstatus.tah = getbit(me, 53) ? HEADING_GROUND_TRACK : mm->opstatus.hrd;
}
break;
}
}
}
static void decodeExtendedSquitter(struct modesMessage *mm)
{
unsigned char *me = mm->ME;
unsigned metype = mm->metype = getbits(me, 1, 5);
unsigned check_imf = 0;
// Check CF on DF18 to work out the format of the ES and whether we need to look for an IMF bit
if (mm->msgtype == 18) {
switch (mm->CF) {
case 0: // ADS-B Message from a non-transponder device, AA field holds 24-bit ICAO aircraft address
mm->addrtype = ADDR_ADSB_ICAO_NT;
break;
case 1: // Reserved for ADS-B Message in which the AA field holds anonymous address or ground vehicle address or fixed obstruction address
mm->addrtype = ADDR_ADSB_OTHER;
mm->addr |= MODES_NON_ICAO_ADDRESS;
break;
case 2: // Fine TIS-B Message
// IMF=0: AA field contains the 24-bit ICAO aircraft address
// IMF=1: AA field contains the 12-bit Mode A code followed by a 12-bit track file number
mm->source = SOURCE_TISB;
mm->addrtype = ADDR_TISB_ICAO;
check_imf = 1;
break;
case 3: // Coarse TIS-B airborne position and velocity.
// IMF=0: AA field contains the 24-bit ICAO aircraft address
// IMF=1: AA field contains the 12-bit Mode A code followed by a 12-bit track file number
// For now we only look at the IMF bit.
mm->source = SOURCE_TISB;
mm->addrtype = ADDR_TISB_ICAO;
if (getbit(me, 1))
setIMF(mm);
return;
case 5: // Fine TIS-B Message, AA field contains a non-ICAO 24-bit address
mm->addrtype = ADDR_TISB_OTHER;
mm->source = SOURCE_TISB;
mm->addr |= MODES_NON_ICAO_ADDRESS;
break;
case 6: // Rebroadcast of ADS-B Message from an alternate data link
// IMF=0: AA field holds 24-bit ICAO aircraft address
// IMF=1: AA field holds anonymous address or ground vehicle address or fixed obstruction address
mm->addrtype = ADDR_ADSR_ICAO;
check_imf = 1;
break;
default: // All others, we don't know the format.
mm->addrtype = ADDR_UNKNOWN;
mm->addr |= MODES_NON_ICAO_ADDRESS; // assume non-ICAO
return;
}
}
switch (metype) {
case 1: case 2: case 3: case 4:
decodeESIdentAndCategory(mm);
break;
case 19:
decodeESAirborneVelocity(mm, check_imf);
break;
case 5: case 6: case 7: case 8:
decodeESSurfacePosition(mm, check_imf);
break;
case 0: // Airborne position, baro altitude only
case 9: case 10: case 11: case 12: case 13: case 14: case 15: case 16: case 17: case 18: // Airborne position, baro
case 20: case 21: case 22: // Airborne position, geometric altitude (HAE or MSL)
decodeESAirbornePosition(mm, check_imf);
break;
case 23:
decodeESTestMessage(mm);
break;
case 24: // Reserved for Surface System Status
break;
case 28:
decodeESAircraftStatus(mm, check_imf);
break;
case 29:
decodeESTargetStatus(mm, check_imf);
break;
case 30: // Aircraft Operational Coordination
break;
case 31:
decodeESOperationalStatus(mm, check_imf);
break;
default:
break;
}
}
static const char *df_names[33] = {
/* 0 */ "Short Air-Air Surveillance",
/* 1 */ NULL,
/* 2 */ NULL,
/* 3 */ NULL,
/* 4 */ "Survelliance, Altitude Reply",
/* 5 */ "Survelliance, Identity Reply",
/* 6 */ NULL,
/* 7 */ NULL,
/* 8 */ NULL,
/* 9 */ NULL,
/* 10 */ NULL,
/* 11 */ "All Call Reply",
/* 12 */ NULL,
/* 13 */ NULL,
/* 14 */ NULL,
/* 15 */ NULL,
/* 16 */ "Long Air-Air ACAS",
/* 17 */ "Extended Squitter",
/* 18 */ "Extended Squitter (Non-Transponder)",
/* 19 */ "Extended Squitter (Military)",
/* 20 */ "Comm-B, Altitude Reply",
/* 21 */ "Comm-B, Identity Reply",
/* 22 */ "Military Use",
/* 23 */ NULL,
/* 24 */ "Comm-D Extended Length Message",
/* 25 */ "Comm-D Extended Length Message",
/* 26 */ "Comm-D Extended Length Message",
/* 27 */ "Comm-D Extended Length Message",
/* 28 */ "Comm-D Extended Length Message",
/* 29 */ "Comm-D Extended Length Message",
/* 30 */ "Comm-D Extended Length Message",
/* 31 */ "Comm-D Extended Length Message",
/* 32 */ "Mode A/C Reply",
};
static const char *df_to_string(unsigned df) {
if (df > 32)
return "out of range";
if (!df_names[df])
return "reserved";
return df_names[df];
}
static const char *altitude_unit_to_string(altitude_unit_t unit) {
switch (unit) {
case UNIT_FEET:
return "ft";
case UNIT_METERS:
return "m";
default:
return "(unknown altitude unit)";
}
}
static const char *airground_to_string(airground_t airground) {
switch (airground) {
case AG_GROUND:
return "ground";
case AG_AIRBORNE:
return "airborne";
case AG_INVALID:
return "invalid";
case AG_UNCERTAIN:
return "airborne?";
default:
return "(unknown airground state)";
}
}
static const char *addrtype_to_string(addrtype_t type) {
switch (type) {
case ADDR_ADSB_ICAO:
return "Mode S / ADS-B";
case ADDR_ADSB_ICAO_NT:
return "ADS-B, non-transponder";
case ADDR_ADSB_OTHER:
return "ADS-B, other addressing scheme";
case ADDR_TISB_ICAO:
return "TIS-B";
case ADDR_TISB_OTHER:
return "TIS-B, other addressing scheme";
case ADDR_TISB_TRACKFILE:
return "TIS-B, Mode A code and track file number";
case ADDR_ADSR_ICAO:
return "ADS-R";
case ADDR_ADSR_OTHER:
return "ADS-R, other addressing scheme";
case ADDR_MODE_A:
return "Mode A";
default:
return "unknown addressing scheme";
}
}
static const char *cpr_type_to_string(cpr_type_t type) {
switch (type) {
case CPR_SURFACE:
return "Surface";
case CPR_AIRBORNE:
return "Airborne";
case CPR_COARSE:
return "TIS-B Coarse";
default:
return "unknown CPR type";
}
}
static const char *heading_type_to_string(heading_type_t type) {
switch (type) {
case HEADING_GROUND_TRACK:
return "Ground track";
case HEADING_MAGNETIC:
return "Mag heading";
case HEADING_TRUE:
return "True heading";
case HEADING_MAGNETIC_OR_TRUE:
return "Heading";
case HEADING_TRACK_OR_HEADING:
return "Track/Heading";
default:
return "unknown heading type";
}
}
static const char *commb_format_to_string(commb_format_t format) {
switch (format) {
case COMMB_EMPTY_RESPONSE:
return "empty response";
case COMMB_DATALINK_CAPS:
return "BDS1,0 Datalink capabilities";
case COMMB_GICB_CAPS:
return "BDS1,7 Common usage GICB capabilities";
case COMMB_AIRCRAFT_IDENT:
return "BDS2,0 Aircraft identification";
case COMMB_ACAS_RA:
return "BDS3,0 ACAS resolution advisory";
case COMMB_VERTICAL_INTENT:
return "BDS4,0 Selected vertical intention";
case COMMB_TRACK_TURN:
return "BDS5,0 Track and turn report";
case COMMB_HEADING_SPEED:
return "BDS6,0 Heading and speed report";
default:
return "unknown format";
}
}
static const char *nav_modes_to_string(nav_modes_t flags)
{
static char buf[128];
buf[0] = 0;
if (flags & NAV_MODE_AUTOPILOT)
strcat(buf, "autopilot ");
if (flags & NAV_MODE_VNAV)
strcat(buf, "vnav ");
if (flags & NAV_MODE_ALT_HOLD)
strcat(buf, "althold ");
if (flags & NAV_MODE_APPROACH)
strcat(buf, "approach ");
if (flags & NAV_MODE_LNAV)
strcat(buf, "lnav ");
if (flags & NAV_MODE_TCAS)
strcat(buf, "tcas ");
if (buf[0] != 0)
buf[strlen(buf)-1] = 0;
return buf;
}
static const char *sil_type_to_string(sil_type_t type)
{
switch (type) {
case SIL_UNKNOWN: return "unknown type";
case SIL_PER_HOUR: return "per flight hour";
case SIL_PER_SAMPLE: return "per sample";
default: return "invalid type";
}
}
static const char *emergency_to_string(emergency_t emergency)
{
switch (emergency) {
case EMERGENCY_NONE: return "no emergency";
case EMERGENCY_GENERAL: return "general emergency (7700)";
case EMERGENCY_LIFEGUARD: return "lifeguard / medical emergency";
case EMERGENCY_MINFUEL: return "minimum fuel";
case EMERGENCY_NORDO: return "no communications (7600)";
case EMERGENCY_UNLAWFUL: return "unlawful interference (7500)";
case EMERGENCY_DOWNED: return "downed aircraft";
default: return "reserved";
}
}
static void print_hex_bytes(unsigned char *data, size_t len) {
size_t i;
for (i = 0; i < len; ++i) {
printf("%02X", (unsigned)data[i]);
}
}
static int esTypeHasSubtype(unsigned metype)
{
if (metype <= 18) {
return 0;
}
if (metype >= 20 && metype <= 22) {
return 0;
}
return 1;
}
static const char *esTypeName(unsigned metype, unsigned mesub)
{
switch (metype) {
case 0:
return "No position information (airborne or surface)";
case 1: case 2: case 3: case 4:
return "Aircraft identification and category";
case 5: case 6: case 7: case 8:
return "Surface position";
case 9: case 10: case 11: case 12:
case 13: case 14: case 15: case 16:
case 17: case 18:
return "Airborne position (barometric altitude)";
case 19:
switch (mesub) {
case 1:
return "Airborne velocity over ground, subsonic";
case 2:
return "Airborne velocity over ground, supersonic";
case 3:
return "Airspeed and heading, subsonic";
case 4:
return "Airspeed and heading, supersonic";
default:
return "Unknown";
}
case 20: case 21: case 22:
return "Airborne position (geometric altitude)";
case 23:
switch (mesub) {
case 0:
return "Test message";
case 7:
return "National use / 1090-WP-15-20 Mode A squawk";
default:
return "Unknown";
}
case 24:
return "Reserved for surface system status";
case 27:
return "Reserved for trajectory change";
case 28:
switch (mesub) {
case 1:
return "Emergency/priority status";
case 2:
return "ACAS RA broadcast";
default:
return "Unknown";
}
case 29:
switch (mesub) {
case 0:
return "Target state and status (V1)";
case 1:
return "Target state and status (V2)";
default:
return "Unknown";
}
case 30:
return "Aircraft Operational Coordination";
case 31: // Aircraft Operational Status
switch (mesub) {
case 0:
return "Aircraft operational status (airborne)";
case 1:
return "Aircraft operational status (surface)";
default:
return "Unknown";
}
default:
return "Unknown";
}
}
void displayModesMessage(struct modesMessage *mm) {
int j;
// Handle only addresses mode first.
if (Modes.onlyaddr) {
printf("%06x\n", mm->addr);
return; // Enough for --onlyaddr mode
}
// Show the raw message.
if (Modes.mlat && mm->timestampMsg) {
printf("@%012" PRIX64, mm->timestampMsg);
} else
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
}
if (mm->msgtype < 32)
printf("CRC: %06x\n", mm->crc);
if (mm->correctedbits != 0)
printf("No. of bit errors fixed: %d\n", mm->correctedbits);
if (mm->signalLevel > 0)
printf("RSSI: %.1f dBFS\n", 10 * log10(mm->signalLevel));
if (mm->score)
printf("Score: %d\n", mm->score);
if (mm->timestampMsg) {
if (mm->timestampMsg == MAGIC_MLAT_TIMESTAMP)
printf("This is a synthetic MLAT message.\n");
else
printf("Time: %.2fus\n", mm->timestampMsg / 12.0);
}
switch (mm->msgtype) {
case 0:
printf("DF:0 addr:%06X VS:%u CC:%u SL:%u RI:%u AC:%u\n",
mm->addr, mm->VS, mm->CC, mm->SL, mm->RI, mm->AC);
break;
case 4:
printf("DF:4 addr:%06X FS:%u DR:%u UM:%u AC:%u\n",
mm->addr, mm->FS, mm->DR, mm->UM, mm->AC);
break;
case 5:
printf("DF:5 addr:%06X FS:%u DR:%u UM:%u ID:%u\n",
mm->addr, mm->FS, mm->DR, mm->UM, mm->ID);
break;
case 11:
printf("DF:11 AA:%06X IID:%u CA:%u\n",
mm->AA, mm->IID, mm->CA);
break;
case 16:
printf("DF:16 addr:%06x VS:%u SL:%u RI:%u AC:%u MV:",
mm->addr, mm->VS, mm->SL, mm->RI, mm->AC);
print_hex_bytes(mm->MV, sizeof(mm->MV));
printf("\n");
break;
case 17:
printf("DF:17 AA:%06X CA:%u ME:",
mm->AA, mm->CA);
print_hex_bytes(mm->ME, sizeof(mm->ME));
printf("\n");
break;
case 18:
printf("DF:18 AA:%06X CF:%u ME:",
mm->AA, mm->CF);
print_hex_bytes(mm->ME, sizeof(mm->ME));
printf("\n");
break;
case 20:
printf("DF:20 addr:%06X FS:%u DR:%u UM:%u AC:%u MB:",
mm->addr, mm->FS, mm->DR, mm->UM, mm->AC);
print_hex_bytes(mm->MB, sizeof(mm->MB));
printf("\n");
break;
case 21:
printf("DF:21 addr:%06x FS:%u DR:%u UM:%u ID:%u MB:",
mm->addr, mm->FS, mm->DR, mm->UM, mm->ID);
print_hex_bytes(mm->MB, sizeof(mm->MB));
printf("\n");
break;
case 24:
case 25:
case 26:
case 27:
case 28:
case 29:
case 30:
case 31:
printf("DF:24 addr:%06x KE:%u ND:%u MD:",
mm->addr, mm->KE, mm->ND);
print_hex_bytes(mm->MD, sizeof(mm->MD));
printf("\n");
break;
}
printf(" %s", df_to_string(mm->msgtype));
if (mm->msgtype == 17 || mm->msgtype == 18) {
if (esTypeHasSubtype(mm->metype)) {
printf(" %s (%u/%u)",
esTypeName(mm->metype, mm->mesub),
mm->metype,
mm->mesub);
} else {
printf(" %s (%u)",
esTypeName(mm->metype, mm->mesub),
mm->metype);
}
}
printf("\n");
if (mm->msgtype == 20 || mm->msgtype == 21) {
printf(" Comm-B format: %s\n", commb_format_to_string(mm->commb_format));
}
if (mm->addr & MODES_NON_ICAO_ADDRESS) {
printf(" Other Address: %06X (%s)\n", mm->addr & 0xFFFFFF, addrtype_to_string(mm->addrtype));
} else {
printf(" ICAO Address: %06X (%s)\n", mm->addr, addrtype_to_string(mm->addrtype));
}
if (mm->airground != AG_INVALID) {
printf(" Air/Ground: %s\n",
airground_to_string(mm->airground));
}
if (mm->altitude_baro_valid) {
printf(" Baro altitude: %d %s\n",
mm->altitude_baro,
altitude_unit_to_string(mm->altitude_baro_unit));
}
if (mm->altitude_geom_valid) {
printf(" Geom altitude: %d %s\n",
mm->altitude_geom,
altitude_unit_to_string(mm->altitude_geom_unit));
}
if (mm->geom_delta_valid) {
printf(" Geom - baro: %d ft\n",
mm->geom_delta);
}
if (mm->heading_valid) {
printf(" %-13s %.1f\n", heading_type_to_string(mm->heading_type), mm->heading);
}
if (mm->track_rate_valid) {
printf(" Track rate: %.2f deg/sec %s\n", mm->track_rate, mm->track_rate < 0 ? "left" : mm->track_rate > 0 ? "right" : "");
}
if (mm->roll_valid) {
printf(" Roll: %.1f degrees %s\n", mm->roll, mm->roll < -0.05 ? "left" : mm->roll > 0.05 ? "right" : "");
}
if (mm->gs_valid) {
printf(" Groundspeed: %.1f kt", mm->gs.selected);
if (mm->gs.v0 != mm->gs.selected) {
printf(" (v0: %.1f kt)", mm->gs.v0);
}
if (mm->gs.v2 != mm->gs.selected) {
printf(" (v2: %.1f kt)", mm->gs.v2);
}
printf("\n");
}
if (mm->ias_valid) {
printf(" IAS: %u kt\n", mm->ias);
}
if (mm->tas_valid) {
printf(" TAS: %u kt\n", mm->tas);
}
if (mm->mach_valid) {
printf(" Mach number: %.3f\n", mm->mach);
}
if (mm->baro_rate_valid) {
printf(" Baro rate: %d ft/min\n", mm->baro_rate);
}
if (mm->geom_rate_valid) {
printf(" Geom rate: %d ft/min\n", mm->geom_rate);
}
if (mm->squawk_valid) {
printf(" Squawk: %04x\n",
mm->squawk);
}
if (mm->callsign_valid) {
printf(" Ident: %s\n",
mm->callsign);
}
if (mm->category_valid) {
printf(" Category: %02X\n",
mm->category);
}
if (mm->cpr_valid) {
printf(" CPR type: %s\n"
" CPR odd flag: %s\n",
cpr_type_to_string(mm->cpr_type),
mm->cpr_odd ? "odd" : "even");
if (mm->cpr_decoded) {
printf(" CPR latitude: %.5f (%u)\n"
" CPR longitude: %.5f (%u)\n"
" CPR decoding: %s\n"
" NIC: %u\n"
" Rc: %.3f km / %.1f NM\n",
mm->decoded_lat,
mm->cpr_lat,
mm->decoded_lon,
mm->cpr_lon,
mm->cpr_relative ? "local" : "global",
mm->decoded_nic,
mm->decoded_rc / 1000.0,
mm->decoded_rc / 1852.0);
} else {
printf(" CPR latitude: (%u)\n"
" CPR longitude: (%u)\n"
" CPR decoding: none\n",
mm->cpr_lat,
mm->cpr_lon);
}
}
if (mm->accuracy.nic_a_valid) {
printf(" NIC-A: %d\n", mm->accuracy.nic_a);
}
if (mm->accuracy.nic_b_valid) {
printf(" NIC-B: %d\n", mm->accuracy.nic_b);
}
if (mm->accuracy.nic_c_valid) {
printf(" NIC-C: %d\n", mm->accuracy.nic_c);
}
if (mm->accuracy.nic_baro_valid) {
printf(" NIC-baro: %d\n", mm->accuracy.nic_baro);
}
if (mm->accuracy.nac_p_valid) {
printf(" NACp: %d\n", mm->accuracy.nac_p);
}
if (mm->accuracy.nac_v_valid) {
printf(" NACv: %d\n", mm->accuracy.nac_v);
}
if (mm->accuracy.gva_valid) {
printf(" GVA: %d\n", mm->accuracy.gva);
}
if (mm->accuracy.sil_type != SIL_INVALID) {
const char *sil_description;
switch (mm->accuracy.sil) {
case 1:
sil_description = "p <= 0.1%";
break;
case 2:
sil_description = "p <= 0.001%";
break;
case 3:
sil_description = "p <= 0.00001%";
break;
default:
sil_description = "p > 0.1%";
break;
}
printf(" SIL: %d (%s, %s)\n",
mm->accuracy.sil,
sil_description,
sil_type_to_string(mm->accuracy.sil_type));
}
if (mm->accuracy.sda_valid) {
printf(" SDA: %d\n", mm->accuracy.sda);
}
if (mm->opstatus.valid) {
printf(" Aircraft Operational Status:\n");
printf(" Version: %d\n", mm->opstatus.version);
printf(" Capability classes: ");
if (mm->opstatus.cc_acas) printf("ACAS ");
if (mm->opstatus.cc_cdti) printf("CDTI ");
if (mm->opstatus.cc_1090_in) printf("1090IN ");
if (mm->opstatus.cc_arv) printf("ARV ");
if (mm->opstatus.cc_ts) printf("TS ");
if (mm->opstatus.cc_tc) printf("TC=%d ", mm->opstatus.cc_tc);
if (mm->opstatus.cc_uat_in) printf("UATIN ");
if (mm->opstatus.cc_poa) printf("POA ");
if (mm->opstatus.cc_b2_low) printf("B2-LOW ");
if (mm->opstatus.cc_lw_valid) printf("L/W=%d ", mm->opstatus.cc_lw);
if (mm->opstatus.cc_antenna_offset) printf("GPS-OFFSET=%d ", mm->opstatus.cc_antenna_offset);
printf("\n");
printf(" Operational modes: ");
if (mm->opstatus.om_acas_ra) printf("ACASRA ");
if (mm->opstatus.om_ident) printf("IDENT ");
if (mm->opstatus.om_atc) printf("ATC ");
if (mm->opstatus.om_saf) printf("SAF ");
printf("\n");
if (mm->mesub == 1)
printf(" Track/heading: %s\n", heading_type_to_string(mm->opstatus.tah));
printf(" Heading ref dir: %s\n", heading_type_to_string(mm->opstatus.hrd));
}
if (mm->nav.heading_valid)
printf(" Selected heading: %.1f\n", mm->nav.heading);
if (mm->nav.fms_altitude_valid)
printf(" FMS selected altitude: %u ft\n", mm->nav.fms_altitude);
if (mm->nav.mcp_altitude_valid)
printf(" MCP selected altitude: %u ft\n", mm->nav.mcp_altitude);
if (mm->nav.qnh_valid)
printf(" QNH: %.1f millibars\n", mm->nav.qnh);
if (mm->nav.altitude_source != NAV_ALT_INVALID) {
printf(" Target altitude source: ");
switch (mm->nav.altitude_source) {
case NAV_ALT_AIRCRAFT:
printf("aircraft altitude\n");
break;
case NAV_ALT_MCP:
printf("MCP selected altitude\n");
break;
case NAV_ALT_FMS:
printf("FMS selected altitude\n");
break;
default:
printf("unknown\n");
}
}
if (mm->nav.modes_valid) {
printf(" Nav modes: %s\n", nav_modes_to_string(mm->nav.modes));
}
if (mm->emergency_valid) {
printf(" Emergency/priority: %s\n", emergency_to_string(mm->emergency));
}
printf("\n");
fflush(stdout);
}
//
//=========================================================================
//
// 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) {
struct aircraft *a;
++Modes.stats_current.messages_total;
// Track aircraft state
a = trackUpdateFromMessage(mm);
// In non-interactive non-quiet mode, display messages on standard output
if (!Modes.interactive && !Modes.quiet && (!Modes.show_only || mm->addr == Modes.show_only)) {
displayModesMessage(mm);
}
// Feed output clients.
// If in --net-verbatim mode, do this for all messages.
// Otherwise, apply a sanity-check filter and only
// forward messages when we have seen two of them.
if (Modes.net) {
if (Modes.net_verbatim || mm->msgtype == 32) {
// Unconditionally send
modesQueueOutput(mm, a);
} else if (a->messages > 1) {
// If this is the second message, and we
// squelched the first message, then re-emit the
// first message now.
if (!Modes.net_verbatim && a && a->messages == 2) {
modesQueueOutput(&a->first_message, a);
}
modesQueueOutput(mm, a);
}
}
}
//
// ===================== Mode S detection and decoding ===================
//
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