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Merge pull request #818 from Brumi-2021/ADSB_squawk_investigation

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Correct squawk id in ADSB TX
This commit is contained in:
gullradriel
2023-03-04 08:10:43 +01:00
committed by GitHub
parent f0b4914186 988404df9c
commit 3c13161273
5 changed files with 107 additions and 39 deletions
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2
firmware/application/apps/ui_adsb_tx.cpp
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@@ -207,7 +207,7 @@ void ADSBSquawkView::collect_frames(const uint32_t ICAO_address, std::vector<ADS
ADSBFrame temp_frame;
(void)ICAO_address;
encode_frame_squawk(temp_frame, field_squawk.value_dec_u32());
encode_frame_squawk(temp_frame, field_squawk.concatenate_4_octal_u16());
frame_list.emplace_back(temp_frame);
}

124
firmware/common/adsb.cpp
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@@ -30,21 +30,28 @@ namespace adsb {
void make_frame_adsb(ADSBFrame& frame, const uint32_t ICAO_address) {
frame.clear();
frame.push_byte((DF_ADSB << 3) | 5); // DF and CA
frame.push_byte((DF_ADSB << 3) | 5); // DF=17 and CA
frame.push_byte(ICAO_address >> 16);
frame.push_byte(ICAO_address >> 8);
frame.push_byte(ICAO_address & 0xFF);
}
// Civil aircraft ADS-B message type starts with Dowlink Format (DF=17) and frame is 112 bits long.
// All known DF's >=16 are long (112 bits). All known DF's <=15 are short (56 bits).(In this case 112 bits)
// Msg structure consists of five main parts :|DF=17 (5 bits)|CA (3 bits)|ICAO (24 bits)|ME (56 bits)|CRC (24 bits)
// Aircraft identification and category message structure, the ME (56 bits) = TC,5 bits | CA,3 bits | C1,6 bits | C2,6 bits | C3,6 | C4,6 | C5,6 | C6,6 | C7,6 | C8,6
// TC : (1..4) : Aircraft identification Type Code . // TC : 9 to 18: Airbone postion // TC : 19 Airbone velocity .
// In this encode_frame_identification function we are using DF = 17 (112 bits long) and TC=4)
void encode_frame_id(ADSBFrame& frame, const uint32_t ICAO_address, const std::string& callsign) {
std::string callsign_formatted(8, '_');
uint64_t callsign_coded = 0;
uint32_t c, s;
char ch;
make_frame_adsb(frame, ICAO_address);
make_frame_adsb(frame, ICAO_address); // Header DF=17 Downlink Format = ADS-B message (frame 112 bits)
frame.push_byte(TC_IDENT << 3); // No aircraft category
frame.push_byte(TC_IDENT << 3); // 5 top bits ME = TC = we use fix 4 , # Type aircraft Identification Category = TC_IDENT = 4,
// Translate and encode callsign
for (c = 0; c < 8; c++) {
@@ -101,42 +108,77 @@ std::string decode_frame_id(ADSBFrame& frame) {
frame.make_CRC();
}*/
void encode_frame_squawk(ADSBFrame& frame, const uint32_t squawk) {
uint32_t squawk_coded;
// Mode S services. (Mode Select Beacon System). There are two types of Mode S interrogations: The short (56 bits) . and the long (112 bits )
// All known DF's >=16 are long frame msg (112 bits). All known DF's <=15 are short frame msgs (56 bits).(In this case 112 bits)
// Identity squawk replies can be DF=5 (Surveillance Identity reply)(56 bits) / DF 21 (Comm-B with Identity reply) (112 bits)
// DF 21: Comm-B with identity reply structure = |DF=21(5 bits)|FS (3 bits)|DR (5 bits)|UM (6 bits) |Identity squawk code (13 bits) |MB (56 bits) |CRC (24 bits) (total 112 bits)
// Comm-B messages count for a large portion of the Mode S selective interrogation responses.(means, only transmitted information upon selective request)
// Comm-B messages protocol supports many different types of msg's (up to 255).The three more popular ones are the following ones:
// (a) Mode S ELementary Surveillance (ELS) / (b) Mode S EnHanced Surveillance (EHS) / (c) Meteorological information
// Comm-B Data Selector (BDS) is an 8-bit code that determines which information to be included in the MB fields
void encode_frame_squawk(ADSBFrame& frame, const uint16_t squawk) {
uint16_t squawk_coded;
uint8_t UM_field=0b111101, FS=0b010, DR=0b00001 ;
// To be sent those fields, (56 bits). We should store byte by byte into the frame , and It will be transmitted byte to byte same FIFO order.
// DF 5 bits 5 DF=21 (5 top bits) Downlink Format
// FS 3 bits 0b000, FS (3 bottom bits) (Flight status ) = 000 : no alert, no SPI, aircraft is airborne
// DR 5 bits 0b00001 DR (Downlink request) (5 top bits) = 00000 : no downlink request (In surveillance replies, only values 0, 1, 4, and 5 are used.)
// UM 6 bits 0b000010 UM (Utility message)= 000000, Utility message (UM): 6 bits, contains transponder communication status information.(IIS + IDS)
// Identity_code 13 bits squawk id_code in special interleaved format.
// MB 56 bits
// CRC partity 24 bits parity checksum , cyclic redundancy chek.
frame.clear();
frame.push_byte( ( DF_EHS_SQUAWK << 3 ) | FS ); // DF=21 (5bits) + FS (3bits, 010 : alert, NO SPI, aircraft is airborne)
frame.push_byte(( DR <<3 ) | ( UM_field>>3) ); // DR (5bits, 00001 : downlink request + 3 top bits of UM , let's use 0b111000
frame.push_byte(DF_EHS_SQUAWK << 3); // DF
frame.push_byte(0);
// 12 11 10 9 8 7 6 5 4 3 2 1 0
// 31 30 29 28 27 26 25 24 23 22 21 20 19
// D4 B4 D2 B2 D1 B1 __ A4 C4 A2 C2 A1 C1
// 12 11 10 9 8 7 6 5 4 3 2 1 0 (Original notes) bit weight position----------------------
// 32 31 30 29 28 27 26 25 24 23 22 21 20 (it was wrong , now corrected) bit order inside frame msg
// D4 B4 D2 B2 D1 B1 __ A4 C4 A2 C2 A1 C1 standard spec order of the 13 bits, to be sent , each octal digit = 3 bits , (example A=7 binary A4 A2 A0 = 111
// ABCD = code (octal, 0000~7777)
// FEDCBA9876543210
// xAAAxBBBxCCCxDDD
// x421x421x421x421
squawk_coded = ((squawk << 10) & 0x1000) | // D4
((squawk << 1) & 0x0800) | // B4
((squawk << 9) & 0x0400) | // D2
((squawk << 0) & 0x0200) | // B2
((squawk << 8) & 0x0100) | // D1
((squawk >> 1) & 0x0080) | // B1
((squawk >> 9) & 0x0020) | // A4
((squawk >> 2) & 0x0010) | // C4
((squawk >> 10) & 0x0008) | // A2
((squawk >> 3) & 0x0004) | // C2
((squawk >> 11) & 0x0002) | // A1
((squawk >> 4) & 0x0001); // C1
frame.push_byte(squawk_coded >> 5);
frame.push_byte(squawk_coded << 3);
// FEDCBA9876543210
// xAAAxBBBxCCCxDDD 4 x 3 bits (each octal digit)
// x421x421x421x421 binary weight of each binary position, example AAA = 7 = 111 -------------------------
// Additional , expanded notes -------------------------------
// Identity squawk code ABCD = code (octal, 0000~7777) , input concatenated squawk : 4 octal digits ,A4 A2 A1-B4 B2 B1-C4 C2 C1-D4 D2 D1.
// 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 bit position of the frame msg, (Squawk id is bit 20-32, from C1..D4).
// UM4 UM2 UM1 C1 A1 C2 A2 C4 A4 X B1 D1 B2 D2 B4 D4 3 lower bit UM4,UM2,UM1 of the UM (6bits), and we should re-order the 13 bits ABCD changing 12 bit poistion based on std.
// 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Two bytes , bit position to be send.
squawk_coded = ( (( UM_field & (0b111)) <<13) | ((squawk << 9) & 0x1000) ) | // C1 It also leaves in the top 3 lower bottom bitd part of UM field.
((squawk << 2) & 0x0800) | // A1
((squawk << 6) & 0x0400) | // C2
((squawk >> 1) & 0x0200) | // A2
((squawk << 3) & 0x0100) | // C4
((squawk >> 4) & 0x0080) | // A4
((squawk >> 1) & 0x0020) | // B1
((squawk << 4) & 0x0010) | // D1
((squawk >> 4) & 0x0008) | // B2
((squawk << 1) & 0x0004) | // D2
((squawk >> 7) & 0x0002) | // B4
((squawk >> 2) & 0x0001); // D4
frame.push_byte(squawk_coded>>8); // UM4 UM2 UM1 C1 A1 C2 A2 C4 that is the correct order, confirmed with dump1090
frame.push_byte(squawk_coded); // A4 X(1) B1 D1 B2 D2 B4 D4 that is the correct order, confirmed with dupm1090
// DF 21 messages , has 56 bits more after 13 bits of squawk, we should add MB (56 bits)
// In this example, we are adding fixed MB = Track and turn report (BDS 5,0) decoding MB example = "F9363D3BBF9CE9" (56 bits)
// # -9.7, roll angle (deg)
// # 140.273, track angle (deg)
// # -0.406, track angle rate (deg/s)
// # 476, ground speed (kt)
// # 466, TAS (kt)
frame.push_byte(0xF9);frame.push_byte(0x36);frame.push_byte(0x3D);frame.push_byte(0x3B); // If we deltele those two lines, to send this fixed MB (56 bits),
frame.push_byte(0xBF);frame.push_byte(0x9C);frame.push_byte(0xE9); // current fw is padding with 56 x 0's to complete 112 bits msg.
frame.make_CRC();
}
}
float cpr_mod(float a, float b) {
return a - (b * floor(a / b));
@@ -183,6 +225,13 @@ float cpr_Dlon(float lat, int is_odd) {
return 360.0 / cpr_N(lat, is_odd);
}
// An ADS-B frame Civil aircraft message type starts with Dowlink Format (DF=17) and frame is 112 bits long.
// All known DF's >=16 are long (112 bits). All known DF's <=15 are short (56 bits). (In this case 112 bits)
// Msg structure consists of five main parts :|DF=17 (5 bits)|CA (3 bits)|ICAO (24 bits)|ME (56 bits)|CRC (24 bits)
// Airborne position msg struct, the ME (56 bits) = |TC,5 bits| SS, 2 bits | SAF, 1 | ALT, 12 | T, 1 | F, 1 | LAT-CPR, 17 | LON-CPR, 17
// TC : (1..4) : Aircraft identification Type Code. // TC : 9 to 18: Airbone postion and altitude // TC : 19 Airbone velocity .
// Airborne position message is used to broadcast the position and altitude of the aircraft. It has the Type Code 9–18 and 20–22. (here , we use TC=11)
void encode_frame_pos(ADSBFrame& frame, const uint32_t ICAO_address, const int32_t altitude,
const float latitude, const float longitude, const uint32_t time_parity) {
@@ -190,7 +239,7 @@ void encode_frame_pos(ADSBFrame& frame, const uint32_t ICAO_address, const int32
uint32_t lat, lon;
float delta_lat, yz, rlat, delta_lon, xz;
make_frame_adsb(frame, ICAO_address);
make_frame_adsb(frame, ICAO_address); // Header DF=17 (long frame 112 bits)
frame.push_byte(TC_AIRBORNE_POS << 3); // Bits 2~1: Surveillance Status, bit 0: NICsb
@@ -303,8 +352,11 @@ adsb_pos decode_frame_pos(ADSBFrame& frame_even, ADSBFrame& frame_odd) {
return position;
}
// speed is in knots
// vertical rate is in ft/min
// An ADS-B frame is 112 bits long. Civil aircraft ADS-B message starts with the Downlink Format ,DF=17.
// Msg structure consists of five main parts :|DF=17 (5 bits)|CA (3 bits)|ICAO (24 bits)|ME (56 bits)|CRC (24 bits)
// Airborne velocities are all transmitted with Type Code 19 ( TC=19 ) inside ME (56 bits)
// [units] : speed is in knots, vertical rate climb / descend is in ft/min
void encode_frame_velo(ADSBFrame& frame, const uint32_t ICAO_address, const uint32_t speed,
const float angle, const int32_t v_rate) {
@@ -320,7 +372,7 @@ void encode_frame_velo(ADSBFrame& frame, const uint32_t ICAO_address, const uint
velo_ew_abs = abs(velo_ew) + 1; // encoding Velo speed EW , when sign Direction is 0 (+): West->East, (-) 1: East->West
velo_ns_abs = abs(velo_ns) + 1; // encoding Velo speed NS , when sign Direction is 0 (+): South->North , (-) 1: North->South
make_frame_adsb(frame, ICAO_address);
make_frame_adsb(frame, ICAO_address); // Header DF=17 (long frame 112 bits)
// Airborne velocities are all transmitted with Type Code 19 ( TC=19, using 5 bits ,TC=19 [Binary: 10011]), the following 3 bits are Subt-type Code ,SC= 1,2,3,4
// SC Subtypes code 1 and 2 are used to report ground speeds of aircraft. (SC 3,4 to used to report true airspeed. SC 2,4 are for supersonic aircraft (not used in commercial airline).

5
firmware/common/adsb.hpp
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@@ -33,7 +33,8 @@ namespace adsb {
enum downlink_format {
DF_ADSB = 17,
DF_EHS_SQUAWK = 21
DF_EHS_SQUAWK = 21, // DF 21: Comm-B with identity reply . Mode S enhanced surveillance of squawk + (MB_field = Track and turn report (BDS 5,0)).
// Confirmed that it is Detected correctly by dump1090. and sdrangel.
};
enum type_code {
@@ -104,7 +105,7 @@ adsb_vel decode_frame_velo(ADSBFrame& frame);
//void encode_frame_emergency(ADSBFrame& frame, const uint32_t ICAO_address, const uint8_t code);
void encode_frame_squawk(ADSBFrame& frame, const uint32_t squawk);
void encode_frame_squawk(ADSBFrame& frame, const uint16_t squawk);
} /* namespace adsb */

14
firmware/common/ui_widget.cpp
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@@ -1662,6 +1662,20 @@ SymField::SymField(
set_focusable(true);
}
uint16_t SymField::concatenate_4_octal_u16() {
// input array 4 octal digits , return 12 bits, same order, trippled A4-A2-A1|B4-B2-B1|C4-C2-C1|D4-D2-D1
uint32_t mul = 1; uint16_t v = 0;
if (type_ == SYMFIELD_OCT ) {
for (uint32_t c = 0; c < length_; c++) {
v += values_[(length_ - 1 - c)] * mul;
mul *= 8; // shift 3 bits to the right every new octal squawk digit
}
return v;
} else
return 0;
}
uint32_t SymField::value_dec_u32() {
uint32_t mul = 1, v = 0;

1
firmware/common/ui_widget.hpp
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@@ -676,6 +676,7 @@ public:
void set_sym(const uint32_t index, const uint32_t new_value);
void set_length(const uint32_t new_length);
void set_symbol_list(const uint32_t index, const std::string symbol_list);
uint16_t concatenate_4_octal_u16();
uint32_t value_dec_u32();
uint64_t value_hex_u64();
std::string value_string();