// Part of readsb, a Mode-S/ADSB/TIS message decoder. // // comm_b.c: Comm-B message decoding // // Copyright (c) 2019 Michael Wolf // // This code is based on a detached fork of dump1090-fa. // // Copyright (c) 2017 FlightAware, LLC // Copyright (c) 2017 Oliver Jowett // // This file is free software: you can redistribute it and/or modify // it under the terms of the GNU General Public License as published by // the Free Software Foundation, either version 3 of the License, or // 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 . #include "readsb.h" #include "ais_charset.h" #define M_PI 3.14159265358979323846 typedef int (*CommBDecoderFn)(struct modesMessage *, bool); static int decodeEmptyResponse(struct modesMessage *mm, bool store); static int decodeBDS10(struct modesMessage *mm, bool store); static int decodeBDS17(struct modesMessage *mm, bool store); static int decodeBDS20(struct modesMessage *mm, bool store); static int decodeBDS30(struct modesMessage *mm, bool store); static int decodeBDS40(struct modesMessage *mm, bool store); static int decodeBDS50(struct modesMessage *mm, bool store); static int decodeBDS60(struct modesMessage *mm, bool store); static int decodeBDS44(struct modesMessage *mm, bool store); static CommBDecoderFn comm_b_decoders[] = { &decodeEmptyResponse, &decodeBDS10, &decodeBDS20, &decodeBDS30, &decodeBDS17, &decodeBDS40, &decodeBDS50, &decodeBDS60, &decodeBDS44 }; void decodeCommB(struct modesMessage *mm) { mm->commb_format = COMMB_UNKNOWN; // If DR or UM are set, this message is _probably_ noise // as nothing really seems to use the multisite broadcast stuff? // Also skip anything that had errors corrected if (mm->DR != 0 || mm->UM != 0 || mm->correctedbits > 0) { return; } // This is a bit hairy as we don't know what the requested register was int bestScore = 0; CommBDecoderFn bestDecoder = NULL; int ambiguous = 0; for (unsigned i = 0; i < (sizeof (comm_b_decoders) / sizeof (comm_b_decoders[0])); ++i) { int score = comm_b_decoders[i](mm, false); if (score > bestScore) { bestScore = score; bestDecoder = comm_b_decoders[i]; ambiguous = 0; } else if (score == bestScore) { ambiguous = 1; } } if (bestDecoder) { if (ambiguous) { mm->commb_format = COMMB_AMBIGUOUS; } else { // decode it bestDecoder(mm, true); } } } static int decodeEmptyResponse(struct modesMessage *mm, bool store) { for (unsigned i = 0; i < 7; ++i) { if (mm->MB[i] != 0) { return 0; } } if (store) { mm->commb_format = COMMB_EMPTY_RESPONSE; } return 56; } // BDS1,0 Datalink capabilities static int decodeBDS10(struct modesMessage *mm, bool store) { unsigned char *msg = mm->MB; // BDS identifier if (msg[0] != 0x10) { return 0; } // Reserved bits if (getbits(msg, 10, 14) != 0) { return 0; } // Looks plausible. if (store) { mm->commb_format = COMMB_DATALINK_CAPS; } return 56; } // BDS1,7 Common usage GICB capability report static int decodeBDS17(struct modesMessage *mm, bool store) { unsigned char *msg = mm->MB; // reserved bits if (getbits(msg, 25, 56) != 0) { return 0; } int score = 0; if (getbit(msg, 7)) { score += 1; // 2,0 aircraft identification } else { // BDS2,0 is on almost everything score -= 2; } // unlikely bits if (getbit(msg, 10)) { // 4,1 next waypoint identifier score -= 2; } if (getbit(msg, 11)) { // 4,2 next waypoint position score -= 2; } if (getbit(msg, 12)) { // 4,3 next waypoint information score -= 2; } if (getbit(msg, 13)) { // 4,4 meterological routine report score -= 2; } if (getbit(msg, 14)) { // 4,4 meterological hazard report score -= 2; } if (getbit(msg, 20)) { // 5,4 waypoint 1 score -= 2; } if (getbit(msg, 21)) { // 5,5 waypoint 2 score -= 2; } if (getbit(msg, 22)) { // 5,6 waypoint 3 score -= 2; } if (getbit(msg, 1) && getbit(msg, 2) && getbit(msg, 3) && getbit(msg, 4) && getbit(msg, 5)) { // looks like ES capable score += 5; if (getbit(msg, 6)) { // ES EDI score += 1; } } else if (!getbit(msg, 1) && !getbit(msg, 2) && !getbit(msg, 3) && !getbit(msg, 4) && !getbit(msg, 5) && !getbit(msg, 6)) { // not ES capable score += 1; } else { // partial ES support, unlikely score -= 12; } if (getbit(msg, 16) && getbit(msg, 24)) { // track/turn, heading/speed score += 2; if (getbit(msg, 9)) { // vertical intent score += 1; } } else if (!getbit(msg, 16) && !getbit(msg, 24) && !getbit(msg, 9)) { // neither score += 1; } else { // unlikely score -= 6; } if (store) { mm->commb_format = COMMB_GICB_CAPS; } return score; } // BDS2,0 Aircraft identification static int decodeBDS20(struct modesMessage *mm, bool store) { char callsign[sizeof(mm->callsign)]; unsigned char *msg = mm->MB; // BDS identifier if (msg[0] != 0x20) { return 0; } callsign[0] = ais_charset[getbits(msg, 9, 14)]; callsign[1] = ais_charset[getbits(msg, 15, 20)]; callsign[2] = ais_charset[getbits(msg, 21, 26)]; callsign[3] = ais_charset[getbits(msg, 27, 32)]; callsign[4] = ais_charset[getbits(msg, 33, 38)]; callsign[5] = ais_charset[getbits(msg, 39, 44)]; callsign[6] = ais_charset[getbits(msg, 45, 50)]; callsign[7] = ais_charset[getbits(msg, 51, 56)]; callsign[8] = 0; // score based on number of valid characters int score = 8; int valid = 1; for (int i = 0; i < 8; ++i) { if ( (callsign[i] >= 'A' && callsign[i] <= 'Z') // -./0123456789 || (callsign[i] >= '-' && callsign[i] <= '9') || callsign[i] == ' ' || callsign[i] == '@' ) { // valid chars score += 6; } else { // Invalid if (Modes.debug_callsign) { fprintf(stderr, "%06x %8s (len: %d)\n", mm->addr, callsign, (int) strlen(callsign)); } return 0; } } if (store) { mm->commb_format = COMMB_AIRCRAFT_IDENT; if (valid) { memcpy(mm->callsign, callsign, sizeof(mm->callsign)); mm->callsign_valid = 1; } } return score; } // check if the payload is a valid ACAS payload // https://mode-s.org/decode/book-the_1090mhz_riddle-junzi_sun.pdf int checkAcasRaValid(unsigned char *msg, struct modesMessage *mm, int debug) { bool ara = getbit(msg, 9); bool rat = getbit(msg, 27); bool mte = getbit(msg, 28); // not a valid RA if none of the bits are set if (!ara && !rat && !mte) return 0; if (getbits(msg, 9, 28) == 0) return 0; // these are the bits that contain the info, all zero it's not an RA if (getbit(msg, 23) && getbit(msg, 24)) return 0; // complementary bits, both set is invalid (above / below) if (getbit(msg, 25) && getbit(msg, 26)) return 0; // complementary bits, both set is invalid (left / right) if (mm->msgtype == 16) { if (getbits(msg, 29, 56) != 0) return 0; // in DF16 messages msg bits 29 to 56 are reserved return 1; } // some extra restrictions for DF != 16 below if (getbit(msg, 25) || getbit(msg, 26)) return 0; // left / right isn't used, require zero // for COMMB messages let's check if the thread indicator makes sense int tti = getbits(msg, 29, 30); // thread type indicator // 00 No identity data in threat identity data if (tti == 0) { if (getbits(msg, 31, 56) != 0) return 0; return 1; } // When the threat type indicator is 01 , MB bits 31-54 contain the 24-bit Mode S transponder address and the last two bits are set to zero. if (tti == 1) { if (getbits(msg, 55, 56) != 0) return 0; uint32_t addr = getbits(msg, 31, 54); if (icaoFilterTest(addr)) return 1; return debug; // zero unless debug } // 10 Threat identity data contains altitude, range, and bearing if (tti == 2) { if (mm->metype == 28)// allow for DF17 return 1; // hard to tell if used and separate from garbage, don't mark valid for the moment return debug; // zero unless debug } // 11 Not assigned if (tti == 3) { return 0; } return 0; } // BDS3,0 ACAS RA static int decodeBDS30(struct modesMessage *mm, bool store) { unsigned char *msg = mm->MB; // BDS identifier if (msg[0] != 0x30) { return 0; } if (store) { mm->commb_format = COMMB_ACAS_RA; mm->acas_ra_valid = 1; } // just accept it. return 56; } // BDS4,0 Selected vertical intention static int decodeBDS40(struct modesMessage *mm, bool store) { unsigned char *msg = mm->MB; unsigned mcp_valid = getbit(msg, 1); unsigned mcp_raw = getbits(msg, 2, 13); unsigned fms_valid = getbit(msg, 14); unsigned fms_raw = getbits(msg, 15, 26); unsigned baro_valid = getbit(msg, 27); unsigned baro_raw = getbits(msg, 28, 39); unsigned reserved_1 = getbits(msg, 40, 47); unsigned mode_valid = getbit(msg, 48); unsigned mode_raw = getbits(msg, 49, 51); unsigned reserved_2 = getbits(msg, 52, 53); unsigned source_valid = getbit(msg, 54); unsigned source_raw = getbits(msg, 55, 56); if (!mcp_valid && !fms_valid && !baro_valid && !mode_valid && !source_valid) { return 0; } int score = 0; unsigned mcp_alt = 0; if (mcp_valid && mcp_raw != 0) { mcp_alt = mcp_raw * 16; if (mcp_alt >= 1000 && mcp_alt <= 50000) { score += 13; } else { // unlikely altitude return 0; } } else if (!mcp_valid && mcp_raw == 0) { score += 1; } else { return 0; } unsigned fms_alt = 0; if (fms_valid && fms_raw != 0) { fms_alt = fms_raw * 16; if (fms_alt >= 1000 && fms_alt <= 50000) { score += 13; } else { // unlikely altitude return 0; } } else if (!fms_valid && fms_raw == 0) { score += 1; } else { return 0; } float baro_setting = 0; if (baro_valid && baro_raw != 0) { baro_setting = 800 + baro_raw * 0.1; if (baro_setting >= 900 && baro_setting <= 1100) { score += 13; } else { // unlikely pressure setting return 0; } } else if (!baro_valid && baro_raw == 0) { score += 1; } else { return 0; } if (reserved_1 != 0) { return 0; } if (mode_valid) { score += 4; } else if (!mode_valid && mode_raw == 0) { score += 1; } else { return 0; } if (reserved_2 != 0) { return 0; } if (source_valid) { score += 3; } else if (!source_valid && source_raw == 0) { score += 1; } else { return 0; } // small penalty for inconsistent data if (mcp_valid && fms_valid && mcp_alt != fms_alt) { score -= 4; } if (mcp_valid) { unsigned remainder = mcp_alt % 500; if (!(remainder < 16 || remainder > 484)) { // mcp altitude is not a multiple of 500 score -= 4; } } if (fms_valid) { unsigned remainder = fms_alt % 500; if (!(remainder < 16 || remainder > 484)) { // fms altitude is not a multiple of 500 score -= 4; } } if (store) { mm->commb_format = COMMB_VERTICAL_INTENT; if (mcp_valid) { mm->nav.mcp_altitude_valid = 1; mm->nav.mcp_altitude = mcp_alt; } if (fms_valid) { mm->nav.fms_altitude_valid = 1; mm->nav.fms_altitude = fms_alt; } if (baro_valid) { mm->nav.qnh_valid = 1; mm->nav.qnh = baro_setting; } if (mode_valid) { mm->nav.modes_valid = 1; mm->nav.modes = ((mode_raw & 4) ? NAV_MODE_VNAV : 0) | ((mode_raw & 2) ? NAV_MODE_ALT_HOLD : 0) | ((mode_raw & 1) ? NAV_MODE_APPROACH : 0); } if (source_valid) { switch (source_raw) { case 0: mm->nav.altitude_source = NAV_ALT_UNKNOWN; break; case 1: mm->nav.altitude_source = NAV_ALT_AIRCRAFT; break; case 2: mm->nav.altitude_source = NAV_ALT_MCP; break; case 3: mm->nav.altitude_source = NAV_ALT_FMS; break; default: mm->nav.altitude_source = NAV_ALT_INVALID; break; } } else { mm->nav.altitude_source = NAV_ALT_INVALID; } } return score; } // BDS5,0 Track and turn report static int decodeBDS50(struct modesMessage *mm, bool store) { unsigned char *msg = mm->MB; unsigned roll_valid = getbit(msg, 1); unsigned roll_sign = getbit(msg, 2); unsigned roll_raw = getbits(msg, 3, 11); unsigned track_valid = getbit(msg, 12); unsigned track_sign = getbit(msg, 13); unsigned track_raw = getbits(msg, 14, 23); unsigned gs_valid = getbit(msg, 24); unsigned gs_raw = getbits(msg, 25, 34); unsigned track_rate_valid = getbit(msg, 35); unsigned track_rate_sign = getbit(msg, 36); unsigned track_rate_raw = getbits(msg, 37, 45); unsigned tas_valid = getbit(msg, 46); unsigned tas_raw = getbits(msg, 47, 56); if (!roll_valid || !track_valid || !gs_valid || !tas_valid) { return 0; } int score = 0; float roll = 0; if (roll_valid) { roll = roll_raw * 45.0 / 256.0; if (roll_sign) { roll -= 90.0; } if (roll >= -40 && roll < 40) { score += 11; } else { return 0; } } else if (!roll_valid && roll_raw == 0 && !roll_sign) { score += 1; } else { return 0; } float track = 0; if (track_valid) { score += 12; track = track_raw * 90.0 / 512.0; if (track_sign) { track += 180.0; } } else if (!track_valid && track_raw == 0 && !track_sign) { score += 1; } else { return 0; } unsigned gs = 0; if (gs_valid && gs_raw != 0) { gs = gs_raw * 2; if (gs >= 50 && gs <= 700) { score += 11; } else { return 0; } } else if (!gs_valid && gs_raw == 0) { score += 1; } else { return 0; } float track_rate = 0; if (track_rate_valid) { track_rate = track_rate_raw * 8.0 / 256.0; if (track_rate_sign) { track_rate -= 16; } if (track_rate >= -10.0 && track_rate <= 10.0) { score += 11; } else { return 0; } } else if (!track_rate_valid && track_rate_raw == 0 && !track_rate_sign) { score += 1; } else { return 0; } unsigned tas = 0; if (tas_valid && tas_raw != 0) { tas = tas_raw * 2; if (tas >= 50 && tas <= 700) { score += 11; } else { return 0; } } else if (!tas_valid && tas_raw == 0) { score += 1; } else { return 0; } // small penalty for inconsistent data if (gs_valid && tas_valid) { int delta = abs((int)gs_valid - (int)tas_valid); if (delta > 150) { score -= 6; } } // compute the theoretical turn rate and compare to track angle rate if (roll_valid && tas_valid && tas > 0 && track_rate_valid) { double turn_rate = 68625 * tan(roll * M_PI / 180.0) / (tas * 20 * M_PI); double delta = fabs(turn_rate - track_rate); if (delta > 2.0) { score -= 6; } } if (store) { mm->commb_format = COMMB_TRACK_TURN; if (roll_valid) { mm->roll_valid = 1; mm->roll = roll; } if (track_valid) { mm->heading_valid = 1; mm->heading = track; mm->heading_type = HEADING_GROUND_TRACK; } if (gs_valid) { mm->gs_valid = 1; mm->gs.v0 = mm->gs.v2 = mm->gs.selected = gs; } if (track_rate_valid) { mm->track_rate_valid = 1; mm->track_rate = track_rate; } if (tas_valid) { mm->tas_valid = 1; mm->tas = tas; } } return score; } // BDS6,0 Heading and speed report static int decodeBDS60(struct modesMessage *mm, bool store) { unsigned char *msg = mm->MB; unsigned heading_valid = getbit(msg, 1); unsigned heading_sign = getbit(msg, 2); unsigned heading_raw = getbits(msg, 3, 12); unsigned ias_valid = getbit(msg, 13); unsigned ias_raw = getbits(msg, 14, 23); unsigned mach_valid = getbit(msg, 24); unsigned mach_raw = getbits(msg, 25, 34); unsigned baro_rate_valid = getbit(msg, 35); unsigned baro_rate_sign = getbit(msg, 36); unsigned baro_rate_raw = getbits(msg, 37, 45); unsigned inertial_rate_valid = getbit(msg, 46); unsigned inertial_rate_sign = getbit(msg, 47); unsigned inertial_rate_raw = getbits(msg, 48, 56); if (!heading_valid || !ias_valid || !mach_valid || (!baro_rate_valid && !inertial_rate_valid)) { return 0; } int score = 0; float heading = 0; if (heading_valid) { heading = heading_raw * 90.0 / 512.0; if (heading_sign) { heading += 180.0; } score += 12; } else if (!heading_valid && heading_raw == 0 && !heading_sign) { score += 1; } else { return 0; } unsigned ias = 0; if (ias_valid && ias_raw != 0) { ias = ias_raw; if (ias >= 50 && ias <= 700) { score += 11; } else { return 0; } } else if (!ias_valid && ias_raw == 0) { score += 1; } else { return 0; } float mach = 0; if (mach_valid && mach_raw != 0) { mach = mach_raw * 2.048 / 512; if (mach >= 0.1 && mach <= 0.9) { score += 11; } else { return 0; } } else if (!mach_valid && mach_raw == 0) { score += 1; } else { return 0; } int baro_rate = 0; if (baro_rate_valid) { baro_rate = baro_rate_raw * 32; if (baro_rate_sign) { baro_rate -= 16384; } if (baro_rate >= -6000 && baro_rate <= 6000) { score += 11; } else { return 0; } } else if (!baro_rate_valid && baro_rate_raw == 0) { score += 1; } else { return 0; } int inertial_rate = 0; if (inertial_rate_valid) { inertial_rate = inertial_rate_raw * 32; if (inertial_rate_sign) { inertial_rate -= 16384; } if (inertial_rate >= -6000 && inertial_rate <= 6000) { score += 11; } else { return 0; } } else if (!inertial_rate_valid && inertial_rate_raw == 0) { score += 1; } else { return 0; } // small penalty for inconsistent data // Should check IAS vs Mach at given altitude, but the maths is a little involved if (baro_rate_valid && inertial_rate_valid) { int delta = abs(baro_rate - inertial_rate); if (delta > 2000) { score -= 12; } } if (store) { mm->commb_format = COMMB_HEADING_SPEED; if (heading_valid) { mm->heading_valid = 1; mm->heading = heading; mm->heading_type = HEADING_MAGNETIC; } if (ias_valid) { mm->ias_valid = 1; mm->ias = ias; } if (mach_valid) { mm->mach_valid = 1; mm->mach = mach; } if (baro_rate_valid) { mm->baro_rate_valid = 1; mm->baro_rate = baro_rate; } if (inertial_rate_valid) { // INS-derived data is treated as a "geometric rate" / "geometric altitude" // elsewhere, so do the same here. mm->geom_rate_valid = 1; mm->geom_rate = inertial_rate; } } return score; } // BDS 4,4 Meteorological routine air report static int decodeBDS44(struct modesMessage *mm, bool store) { unsigned char *msg = mm->MB; unsigned source = getbits(msg, 1, 4); unsigned wind_valid = getbit(msg, 5); unsigned wind_speed_raw = getbits(msg, 6, 14); unsigned wind_direction_raw = getbits(msg, 15, 23); unsigned temperature_sign = getbit(msg, 24); unsigned static_air_temperature_raw = getbits(msg, 25, 34); unsigned pressure_valid = getbit(msg, 35); unsigned static_pressure_raw = getbits(msg, 36, 46); unsigned turbulence_valid = getbit(msg, 47); unsigned turbulence_raw = getbits(msg, 48, 49); unsigned humidity_valid = getbit(msg, 50); unsigned humidity_raw = getbits(msg, 51, 56); /* if (!wind_valid || !temperature_valid || !pressure_valid || !turbulence_valid && !humidity_valid){ return 0; } */ int met_source = source; int score = 0; int wind_speed = 0; float wind_direction = 0; float temperature = 0; int static_pressure = 0; int turbulence = 0; float humidity = 0; if (met_source >= 0 && met_source <= 6) { score += 4; } else { return 0; } if (wind_valid){ wind_speed = (int)wind_speed_raw; if (wind_speed <= 511 && wind_speed >= 0){ score += 9; } else { return 0; } wind_direction = wind_direction_raw * (180 / 256); if (wind_direction >= 0 && wind_direction <= 360){ score += 9; } else { return 0; } } else if (wind_speed == 0) { score += 2; } if (temperature_sign){ temperature = (static_air_temperature_raw - pow(2, 10)) * 0.25; } else { temperature = static_air_temperature_raw * 0.25; } if (temperature >= -128 && temperature <= 128){ score += 10; } else { return 0; } if (pressure_valid){ static_pressure = (int)static_pressure_raw; if (static_pressure >= 0 && static_pressure <= 2048){ score += 11; return 0; } else { } } else if (static_pressure == 0) { score += 1; } if (turbulence_valid){ turbulence = (int)turbulence_raw; if (turbulence >= 0 && turbulence <= 3) { score += 2; } else { return 0; } } else if (turbulence == 0) { score += 1; } if (humidity_valid) { humidity = humidity_raw * (100.0f / 64); if (humidity >= 0 && humidity <= 100){ score += 6; } else { return 0; } } else if (humidity == 0) { score += 1; } if (store) { mm->commb_format = COMMB_METEOROLOGICAL_ROUTINE; mm->met_source_valid = 1; mm->met_source = met_source; if (wind_valid) { mm->wind_valid = 1; mm->wind_speed = wind_speed; mm->wind_direction = wind_direction; } mm->oat_valid = 1; mm->oat = temperature; if (pressure_valid) { mm->static_pressure_valid = 1; mm->static_pressure = static_pressure; } if (turbulence_valid) { mm->turbulence_valid = 1; mm->turbulence = turbulence; } if (humidity_valid) { mm->humidity_valid = 1; mm->humidity = humidity; } } return score; }