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Implement Mode A/C decoding

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First attempt at decoding legacy SSR Modes A and C.

If the command line switch --modeac is used, the program will now
attempt to recover Mode A/C signals contained in the raw I/Q data
stream. The current recovery mechanism is quite strict and does not cope
well with overlapping and corrupt SSR replies. I estimate that less than
20% of possible returns are decoded correctly. Hopefully over the next
few iterations this can be improved.

If outputting raw data it is recommended to use the --net-ro-size and
--net-ro-rate command line options to reduce the number of very small
ethernet packets that will be generated by mode A/C replies.
This commit is contained in:
Malcolm Robb 2013-04-22 23:31:59 +01:00
parent 39cb96f24b
commit 9fff65ba58
1 changed files with 540 additions and 62 deletions
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530
dump1090.c
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@ -56,7 +56,7 @@
// MinorVer changes when additional features are added, but not for bug fixes (range 00-99) // MinorVer changes when additional features are added, but not for bug fixes (range 00-99)
// DayDate & Year changes for all changes, including for bug fixes. It represent the release date of the update // DayDate & Year changes for all changes, including for bug fixes. It represent the release date of the update
// //
#define MODES_DUMP1090_VERSION "1.01.2004.13" #define MODES_DUMP1090_VERSION "1.02.2204.13"
#define MODES_DEFAULT_RATE 2000000 #define MODES_DEFAULT_RATE 2000000
#define MODES_DEFAULT_FREQ 1090000000 #define MODES_DEFAULT_FREQ 1090000000
@ -70,7 +70,11 @@
#define MODES_MSG_SQUELCH_LEVEL 0x02FF /* Average signal strength limit */ #define MODES_MSG_SQUELCH_LEVEL 0x02FF /* Average signal strength limit */
#define MODES_MSG_ENCODER_ERRS 3 /* Maximum number of encoding errors */ #define MODES_MSG_ENCODER_ERRS 3 /* Maximum number of encoding errors */
#define MODEA_MSG_BYTES 2 #define MODEAC_MSG_SAMPLES (25 * 2) /* include up to the SPI bit */
#define MODEAC_MSG_BYTES 2
#define MODEAC_MSG_SQUELCH_LEVEL 0x07FF /* Average signal strength limit */
#define MODEAC_MSG_FLAG (1<<0)
#define MODEAC_MSG_MODES_HIT (1<<1)
#define MODES_PREAMBLE_US 8 /* microseconds = bits */ #define MODES_PREAMBLE_US 8 /* microseconds = bits */
#define MODES_PREAMBLE_SAMPLES (MODES_PREAMBLE_US * 2) #define MODES_PREAMBLE_SAMPLES (MODES_PREAMBLE_US * 2)
@ -139,6 +143,10 @@ struct aircraft {
int track; /* Angle of flight. */ int track; /* Angle of flight. */
time_t seen; /* Time at which the last packet was received. */ time_t seen; /* Time at which the last packet was received. */
long messages; /* Number of Mode S messages received. */ long messages; /* Number of Mode S messages received. */
int modeC; /* Altitude */
long modeAcount; /* Mode A Squawk hit Count */
long modeCcount; /* Mode C Altitude hit Count */
int modeACflags; /* Flags for mode A/C recognition */
/* Encoded latitude and longitude as extracted by odd and even /* Encoded latitude and longitude as extracted by odd and even
* CPR encoded messages. */ * CPR encoded messages. */
int odd_cprlat; int odd_cprlat;
@ -194,6 +202,7 @@ struct {
int check_crc; /* Only display messages with good CRC. */ int check_crc; /* Only display messages with good CRC. */
int raw; /* Raw output format. */ int raw; /* Raw output format. */
int beast; /* Beast binary format output. */ int beast; /* Beast binary format output. */
int mode_ac; /* Enable decoding of SSR Modes A & C. */
int debug; /* Debugging mode. */ int debug; /* Debugging mode. */
int net; /* Enable networking. */ int net; /* Enable networking. */
int net_only; /* Enable just networking. */ int net_only; /* Enable just networking. */
@ -231,6 +240,7 @@ struct {
unsigned int stat_sbs_connections; unsigned int stat_sbs_connections;
unsigned int stat_out_of_phase; unsigned int stat_out_of_phase;
unsigned int stat_DF_Corrected; unsigned int stat_DF_Corrected;
unsigned int stat_ModeAC;
} Modes; } Modes;
/* The struct we use to store information about a decoded message. */ /* The struct we use to store information about a decoded message. */
@ -278,7 +288,7 @@ struct modesMessage {
int identity; /* 13 bits identity (Squawk). */ int identity; /* 13 bits identity (Squawk). */
/* Fields used by multiple message types. */ /* Fields used by multiple message types. */
int altitude, unit; int altitude, unit, modeC;
}; };
void interactiveShowData(void); void interactiveShowData(void);
@ -317,6 +327,7 @@ void modesInitConfig(void) {
Modes.check_crc = 1; Modes.check_crc = 1;
Modes.raw = 0; Modes.raw = 0;
Modes.beast = 0; Modes.beast = 0;
Modes.mode_ac = 0;
Modes.net = 0; Modes.net = 0;
Modes.net_only = 0; Modes.net_only = 0;
Modes.net_output_sbs_port = MODES_NET_OUTPUT_SBS_PORT; Modes.net_output_sbs_port = MODES_NET_OUTPUT_SBS_PORT;
@ -448,6 +459,7 @@ void modesInit(void) {
Modes.stat_sbs_connections = 0; Modes.stat_sbs_connections = 0;
Modes.stat_out_of_phase = 0; Modes.stat_out_of_phase = 0;
Modes.stat_DF_Corrected = 0; Modes.stat_DF_Corrected = 0;
Modes.stat_ModeAC = 0;
Modes.exit = 0; Modes.exit = 0;
} }
@ -541,7 +553,7 @@ void readDataFromFile(void) {
/* When --ifile and --interactive are used together, slow down /* When --ifile and --interactive are used together, slow down
* playing at the natural rate of the RTLSDR received. */ * playing at the natural rate of the RTLSDR received. */
pthread_mutex_unlock(&Modes.data_mutex); pthread_mutex_unlock(&Modes.data_mutex);
usleep(5000); usleep(64000);
pthread_mutex_lock(&Modes.data_mutex); pthread_mutex_lock(&Modes.data_mutex);
} }
@ -708,6 +720,365 @@ void dumpRawMessage(char *descr, unsigned char *msg,
printf("---\n\n"); printf("---\n\n");
} }
/* ===================== Mode A/C detection and decoding =================== */
//
// This table is used to build the Mode A/C variable called ModeABits.Each
// bit period is inspected, and if it's value exceeds the threshold limit,
// then the value in this table is or-ed into ModeABits.
//
// At the end of message processing, ModeABits will be the decoded ModeA value.
//
// We can also flag noise in bits that should be zeros - the xx bits. Noise in
// these bits cause bits (31-16) in ModeABits to be set. Then at the end of message
// processing we can test for errors by looking at these bits.
//
uint32_t ModeABitTable[24] = {
0x00000000, // F1 = 1
0x00000010, // C1
0x00001000, // A1
0x00000020, // C2
0x00002000, // A2
0x00000040, // C4
0x00004000, // A4
0x40000000, // xx = 0 Set bit 30 if we see this high
0x00000100, // B1
0x00000001, // D1
0x00000200, // B2
0x00000002, // D2
0x00000400, // B4
0x00000004, // D4
0x00000000, // F2 = 1
0x08000000, // xx = 0 Set bit 27 if we see this high
0x04000000, // xx = 0 Set bit 26 if we see this high
0x00000080, // SPI
0x02000000, // xx = 0 Set bit 25 if we see this high
0x01000000, // xx = 0 Set bit 24 if we see this high
0x00800000, // xx = 0 Set bit 23 if we see this high
0x00400000, // xx = 0 Set bit 22 if we see this high
0x00200000, // xx = 0 Set bit 21 if we see this high
0x00100000, // xx = 0 Set bit 20 if we see this high
};
//
// This table is used to produce an error variable called ModeAErrs.Each
// inter-bit period is inspected, and if it's value falls outside of the
// expected range, then the value in this table is or-ed into ModeAErrs.
//
// At the end of message processing, ModeAErrs will indicate if we saw
// any inter-bit anomolies, and the bits that are set will show which
// bits had them.
//
uint32_t ModeAMidTable[24] = {
0x80000000, // F1 = 1 Set bit 31 if we see F1_C1 error
0x00000010, // C1 Set bit 4 if we see C1_A1 error
0x00001000, // A1 Set bit 12 if we see A1_C2 error
0x00000020, // C2 Set bit 5 if we see C2_A2 error
0x00002000, // A2 Set bit 13 if we see A2_C4 error
0x00000040, // C4 Set bit 6 if we see C3_A4 error
0x00004000, // A4 Set bit 14 if we see A4_xx error
0x40000000, // xx = 0 Set bit 30 if we see xx_B1 error
0x00000100, // B1 Set bit 8 if we see B1_D1 error
0x00000001, // D1 Set bit 0 if we see D1_B2 error
0x00000200, // B2 Set bit 9 if we see B2_D2 error
0x00000002, // D2 Set bit 1 if we see D2_B4 error
0x00000400, // B4 Set bit 10 if we see B4_D4 error
0x00000004, // D4 Set bit 2 if we see D4_F2 error
0x20000000, // F2 = 1 Set bit 29 if we see F2_xx error
0x08000000, // xx = 0 Set bit 27 if we see xx_xx error
0x04000000, // xx = 0 Set bit 26 if we see xx_SPI error
0x00000080, // SPI Set bit 15 if we see SPI_xx error
0x02000000, // xx = 0 Set bit 25 if we see xx_xx error
0x01000000, // xx = 0 Set bit 24 if we see xx_xx error
0x00800000, // xx = 0 Set bit 23 if we see xx_xx error
0x00400000, // xx = 0 Set bit 22 if we see xx_xx error
0x00200000, // xx = 0 Set bit 21 if we see xx_xx error
0x00100000, // xx = 0 Set bit 20 if we see xx_xx error
};
//
// The "off air" format is,,
// _F1_C1_A1_C2_A2_C4_A4_xx_B1_D1_B2_D2_B4_D4_F2_xx_xx_SPI_
//
// Bit spacing is 1.45uS, with 0.45uS high, and 1.00us low. This is a problem
// because we ase sampling at 2Mhz (500nS) so we are below Nyquist.
//
// The bit spacings are..
// F1 : 0.00,
// 1.45, 2.90, 4.35, 5.80, 7.25, 8.70,
// X : 10.15,
// : 11.60, 13.05, 14.50, 15.95, 17.40, 18.85,
// F2 : 20.30,
// X : 21.75, 23.20, 24.65
//
// This equates to the following sample point centers at 2Mhz.
// [ 0.0],
// [ 2.9], [ 5.8], [ 8.7], [11.6], [14.5], [17.4],
// [20.3],
// [23.2], [26.1], [29.0], [31.9], [34.8], [37.7]
// [40.6]
// [43.5], [46.4], [49.3]
//
// We know that this is a supposed to be a binary stream, so the signal
// should either be a 1 or a 0. Therefore, any energy above the noise level
// in two adjacent samples must be from the same pulse, so we can simply
// add the values together..
//
int detectModeA(uint16_t *m, struct modesMessage *mm)
{
int j, lastBitWasOne;
int ModeABits = 0;
int ModeAErrs = 0;
int byte, bit;
int thisSample, lastBit, lastSpace = 0;
int m0, m1, m2, m3, mPhase;
int n0, n1, n2 ,n3;
int F1_sig, F1_noise;
int F2_sig, F2_noise;
int fSig, fNoise, fLevel, fLoLo;
// m[0] contains the energy from 0 -> 499 nS
// m[1] contains the energy from 500 -> 999 nS
// m[2] contains the energy from 1000 -> 1499 nS
// m[3] contains the energy from 1500 -> 1999 nS
//
// We are looking for a Frame bit (F1) whose width is 450nS, followed by
// 1000nS of quiet.
//
// The width of the frame bit is 450nS, which is 90% of our sample rate.
// Therefore, in an ideal world, all the energy for the frame bit will be
// in a single sample, preceeded by (at least) one zero, and followed by
// two zeros, Best case we can look for ...
//
// 0 - 1 - 0 - 0
//
// However, our samples are not phase aligned, so some of the energy from
// each bit could be spread over two consecutive samples. Worst case is
// that we sample half in one bit, and half in the next. In that case,
// we're looking for
//
// 0 - 0.5 - 0.5 - 0.
m0 = m[0]; m1 = m[1];
if (m0 >= m1) // m1 *must* be bigger than m0 for this to be F1
{return (0);}
m2 = m[2]; m3 = m[3];
//
// if (m2 <= m0), then assume the sample bob on (Phase == 0), so don't look at m3
if ((m2 <= m0) || (m2 < m3))
{m3 = m2; m2 = m0;}
if ( (m3 >= m1) // m1 must be bigger than m3
|| (m0 > m2) // m2 can be equal to m0 if ( 0,1,0,0 )
|| (m3 > m2) ) // m2 can be equal to m3 if ( 0,1,0,0 )
{return (0);}
// m0 = noise
// m1 = noise + (signal * X))
// m2 = noise + (signal * (1-X))
// m3 = noise
//
// Hence, assuming all 4 samples have similar amounts of noise in them
// signal = (m1 + m2) - ((m0 + m3) * 2)
// noise = (m0 + m3) / 2
//
F1_sig = (m1 + m2) - ((m0 + m3) << 1);
F1_noise = (m0 + m3) >> 1;
if ( (F1_sig < MODEAC_MSG_SQUELCH_LEVEL) // minimum required F1 signal amplitude
|| (F1_sig < (F1_noise << 2)) ) // minimum allowable Sig/Noise ratio 4:1
{return (0);}
// If we get here then we have a potential F1, so look for an equally valid F2 20.3uS later
//
// Our F1 is centered somewhere between samples m[1] and m[2]. We can guestimate where F2 is
// by comparing the ratio of m1 and m2, and adding on 20.3 uS (40.6 samples)
//
mPhase = ((m2 * 20) / (m1 + m2));
byte = (mPhase + 812) / 20;
n0 = m[byte++]; n1 = m[byte++];
if (n0 >= n1) // n1 *must* be bigger than n0 for this to be F2
{return (0);}
n2 = m[byte++];
//
// if the sample bob on (Phase == 0), don't look at n3
//
if ((mPhase + 812) % 20)
{n3 = m[byte++];}
else
{n3 = n2; n2 = n0;}
if ( (n3 >= n1) // n1 must be bigger than n3
|| (n0 > n2) // n2 can be equal to n0 ( 0,1,0,0 )
|| (n3 > n2) ) // n2 can be equal to n3 ( 0,1,0,0 )
{return (0);}
F2_sig = (n1 + n2) - ((n0 + n3) << 1);
F2_noise = (n0 + n3) >> 1;
if ( (F2_sig < MODEAC_MSG_SQUELCH_LEVEL) // minimum required F2 signal amplitude
|| (F2_sig < (F2_noise << 2)) ) // maximum allowable Sig/Noise ratio 4:1
{return (0);}
fSig = (F1_sig + F2_sig) >> 1;
fNoise = (F1_noise + F2_noise) >> 1;
fLoLo = fNoise + (fSig >> 2); // 1/2
fLevel = fNoise + (fSig >> 1);
lastBitWasOne = 1;
lastBit = F1_sig;
//
// Now step by a half ModeA bit, 0.725nS, which is 1.45 samples, which is 29/20
// No need to do bit 0 because we've already selected it as a valid F1
// Do several bits past the SPI to increase error rejection
//
for (j = 1, mPhase += 29; j < 48; mPhase += 29, j ++)
{
byte = 1 + (mPhase / 20);
thisSample = m[byte] - fNoise;
if (mPhase % 20) // If the bit is split over two samples...
{thisSample += (m[byte+1] - fNoise);} // add in the second sample's energy
// If we're calculating a space value
if (j & 1)
{lastSpace = thisSample;}
else
{// We're calculating a new bit value
bit = j >> 1;
if (thisSample >= fLevel)
{// We're calculating a new bit value, and its a one
ModeABits |= ModeABitTable[bit--]; // or in the correct bit
if (lastBitWasOne)
{ // This bit is one, last bit was one, so check the last space is somewhere less than one
if ( (lastSpace >= (thisSample>>1)) || (lastSpace >= lastBit) )
{ModeAErrs |= ModeAMidTable[bit];}
}
else
{// This bit,is one, last bit was zero, so check the last space is somewhere less than one
if (lastSpace >= (thisSample >> 1))
{ModeAErrs |= ModeAMidTable[bit];}
}
lastBitWasOne = 1;
}
else
{// We're calculating a new bit value, and its a zero
if (lastBitWasOne)
{ // This bit is zero, last bit was one, so check the last space is somewhere in between
if (lastSpace >= lastBit)
{ModeAErrs |= ModeAMidTable[bit];}
}
else
{// This bit,is zero, last bit was zero, so check the last space is zero too
if (lastSpace >= fLoLo)
{ModeAErrs |= ModeAMidTable[bit];}
}
lastBitWasOne = 0;
}
lastBit = (thisSample >> 1);
}
}
//
// Output format is : 00:A4:A2:A1:00:B4:B2:B1:00:C4:C2:C1:00:D4:D2:D1
//
if ((ModeABits < 3) || (ModeABits & 0xFFFF8808) || (ModeAErrs) )
{return (ModeABits = 0);}
fSig = (fSig + 0x7F) >> 8;
mm->signalLevel = ((fSig < 255) ? fSig : 255);
return ModeABits;
}
// Input format is : 00:A4:A2:A1:00:B4:B2:B1:00:C4:C2:C1:00:D4:D2:D1
int ModeAToModeC(unsigned int ModeA )
{
unsigned int FiveHundreds = 0;
unsigned int OneHundreds = 0;
if ( (ModeA & 0xFFFF888B) // D1 set is illegal. D2 set is > 62700ft which is unlikely
|| ((ModeA & 0x000000F0) == 0) // C1,,C4 cannot be Zero
|| ((ModeA & 0xFFFFFB0F) == 0) ) // Whilst legal, indicates an altitude less than -200 feet
{return -9999;}
if (ModeA & 0x0010) {OneHundreds ^= 0x007;} // C1
if (ModeA & 0x0020) {OneHundreds ^= 0x003;} // C2
if (ModeA & 0x0040) {OneHundreds ^= 0x001;} // C4
// Remove 7s from OneHundreds (Make 7->5, snd 5->7).
if ((OneHundreds & 5) == 5) {OneHundreds ^= 2;}
// Check for invalid codes, only 1 to 5 are valid
if (OneHundreds > 5)
{return -9999;}
//if (ModeA & 0x0001) {FiveHundreds ^= 0x1FF;} // D1 never used for altitude
if (ModeA & 0x0002) {FiveHundreds ^= 0x0FF;} // D2
if (ModeA & 0x0004) {FiveHundreds ^= 0x07F;} // D4
if (ModeA & 0x1000) {FiveHundreds ^= 0x03F;} // A1
if (ModeA & 0x2000) {FiveHundreds ^= 0x01F;} // A2
if (ModeA & 0x4000) {FiveHundreds ^= 0x00F;} // A4
if (ModeA & 0x0100) {FiveHundreds ^= 0x007;} // B1
if (ModeA & 0x0200) {FiveHundreds ^= 0x003;} // B2
if (ModeA & 0x0400) {FiveHundreds ^= 0x001;} // B4
// Correct order of OneHundreds.
if (FiveHundreds & 1) {OneHundreds = 6 - OneHundreds;}
return ((FiveHundreds * 5) + OneHundreds - 13);
}
void decodeModeAMessage(unsigned int ModeA, struct modesMessage *mm)
{
mm->msgtype = 32; // Valid Mode S DF's are DF-00 to DF-31.
// so use 32 to indicate Mode A/C
mm->msgbits = 16; // Fudge up a Mode S style data stream
mm->msg[0] = (ModeA >> 8);
mm->msg[1] = (ModeA);
// Fudge an ICAO address based on Mode A
mm->aa1 = 0xFF; // Use an upper address byte of FF, since this is ICAO unallocated
mm->aa2 = (ModeA >> 8);
mm->aa3 = (ModeA & 0x7F); // remove the Ident bit
// Set the Identity field to decimal ModeA
mm->identity = (ModeA & 7)
+ (((ModeA >> 4) & 7) * 10)
+ (((ModeA >> 8) & 7) * 100)
+ (((ModeA >> 12) & 7) * 1000);
// Flag ident in flight status
mm->fs = ModeA & 0x0080;
// Convert ModeA to ModeC and use as an altitude
mm->modeC = ModeAToModeC(ModeA);
mm->altitude = 0;
// Limit the altitude to sensible values
if ( (mm->modeC < 460) && (mm->modeC >= 0))
{mm->altitude = mm->modeC * 100;}
// Not much else we can tell from a Mode A/C reply.
// Just fudge up a few bits to keep other code happy
mm->crcok = 1;
mm->errorbit = -1;
}
/* ===================== Mode S detection and decoding ===================== */ /* ===================== Mode S detection and decoding ===================== */
/* Parity table for MODE S Messages. /* Parity table for MODE S Messages.
@ -1173,6 +1544,7 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
if (mm->msgtype == 0 || mm->msgtype == 4 || if (mm->msgtype == 0 || mm->msgtype == 4 ||
mm->msgtype == 16 || mm->msgtype == 20) { mm->msgtype == 16 || mm->msgtype == 20) {
mm->altitude = decodeAC13Field(msg, &mm->unit); mm->altitude = decodeAC13Field(msg, &mm->unit);
mm->modeC = (mm->altitude + 49) / 100;
} }
/* Decode extended squitter specific stuff. */ /* Decode extended squitter specific stuff. */
@ -1196,6 +1568,7 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
mm->fflag = msg[6] & (1<<2); mm->fflag = msg[6] & (1<<2);
mm->tflag = msg[6] & (1<<3); mm->tflag = msg[6] & (1<<3);
mm->altitude = decodeAC12Field(msg,&mm->unit); mm->altitude = decodeAC12Field(msg,&mm->unit);
mm->modeC = (mm->altitude + 49) / 100;
mm->raw_latitude = ((msg[6] & 3) << 15) | mm->raw_latitude = ((msg[6] & 3) << 15) |
(msg[7] << 7) | (msg[7] << 7) |
(msg[8] >> 1); (msg[8] >> 1);
@ -1256,7 +1629,7 @@ void displayModesMessage(struct modesMessage *mm) {
/* Show the raw message. */ /* Show the raw message. */
if (Modes.mlat) { if (Modes.mlat) {
printf("@"); //&&& printf("@");
pTimeStamp = (char *) &mm->timestampMsg; pTimeStamp = (char *) &mm->timestampMsg;
for (j=5; j>=0;j--) { for (j=5; j>=0;j--) {
printf("%02X",pTimeStamp[j]); printf("%02X",pTimeStamp[j]);
@ -1272,7 +1645,9 @@ void displayModesMessage(struct modesMessage *mm) {
return; /* Enough for --raw mode */ return; /* Enough for --raw mode */
} }
if (mm->msgtype < 32)
printf("CRC: %06x (%s)\n", (int)mm->crc, mm->crcok ? "ok" : "wrong"); printf("CRC: %06x (%s)\n", (int)mm->crc, mm->crcok ? "ok" : "wrong");
if (mm->errorbit != -1) if (mm->errorbit != -1)
printf("Single bit error fixed, bit %d\n", mm->errorbit); printf("Single bit error fixed, bit %d\n", mm->errorbit);
@ -1362,6 +1737,17 @@ void displayModesMessage(struct modesMessage *mm) {
printf(" Unrecognized ME type: %d subtype: %d\n", printf(" Unrecognized ME type: %d subtype: %d\n",
mm->metype, mm->mesub); mm->metype, mm->mesub);
} }
} else if (mm->msgtype == 32) {
// DF 32 is special code we use for Mode A/C
printf("SSR : Mode A/C Reply.\n");
if (mm->fs & 0x0080) {
printf(" Mode A : %04d IDENT\n", mm->identity);
} else {
printf(" Mode A : %04d\n", mm->identity);
if (mm->altitude >= -1300)
{printf(" Mode C : %d feet\n",mm->altitude);}
}
} else { } else {
if (Modes.check_crc) if (Modes.check_crc)
printf("DF %d with good CRC received " printf("DF %d with good CRC received "
@ -1485,6 +1871,26 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
if (!use_correction) // This is not a re-try with phase correction if (!use_correction) // This is not a re-try with phase correction
{ // so try to find a new preamble { // so try to find a new preamble
if (Modes.mode_ac)
{
struct modesMessage mm;
int ModeA = detectModeA(pPreamble, &mm);
if (ModeA) // We have found a valid ModeA/C in the data
{
mm.timestampMsg = Modes.timestampBlk + ((j+1) * 6);
// Decode the received message and update statistics
decodeModeAMessage(ModeA, &mm);
// Pass data to the next layer
useModesMessage(&mm);
j += MODEAC_MSG_SAMPLES;
Modes.stat_ModeAC++;
continue;
}
}
/* First check of relations between the first 10 samples /* First check of relations between the first 10 samples
* representing a valid preamble. We don't even investigate further * representing a valid preamble. We don't even investigate further
* if this simple test is not passed. */ * if this simple test is not passed. */
@ -1712,19 +2118,23 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
* further processing and visualization. */ * further processing and visualization. */
void useModesMessage(struct modesMessage *mm) { void useModesMessage(struct modesMessage *mm) {
if (!Modes.stats && (Modes.check_crc == 0 || mm->crcok)) { if (!Modes.stats && (Modes.check_crc == 0 || mm->crcok)) {
/* Track aircrafts in interactive mode or if the HTTP // Track aircrafts if...
* interface is enabled. */ if ( (Modes.interactive) // in interactive mode
if (Modes.interactive || Modes.stat_http_requests > 0 || Modes.stat_sbs_connections > 0) { || (Modes.stat_http_requests > 0) // or if the HTTP interface is enabled
|| (Modes.stat_sbs_connections > 0) // or if sbs connections are established
|| (Modes.mode_ac) ) { // or if mode A/C decoding is enabled
struct aircraft *a = interactiveReceiveData(mm); struct aircraft *a = interactiveReceiveData(mm);
if (a && Modes.stat_sbs_connections > 0) modesSendSBSOutput(mm, a); /* Feed SBS output clients. */ if (a && Modes.stat_sbs_connections > 0) modesSendSBSOutput(mm, a); // Feed SBS output clients
} }
/* In non-interactive way, display messages on standard output. */
// In non-interactive mode, display messages on standard output
if (!Modes.interactive && !Modes.quiet) { if (!Modes.interactive && !Modes.quiet) {
displayModesMessage(mm); displayModesMessage(mm);
if (!Modes.raw && !Modes.onlyaddr) printf("\n"); if (!Modes.raw && !Modes.onlyaddr) printf("\n");
} }
/* Send data to connected clients. */
if (Modes.net) { /* Feed raw output clients. */ // Send data to connected network clients
if (Modes.net) {
if (Modes.beast) if (Modes.beast)
modesSendBeastOutput(mm); modesSendBeastOutput(mm);
else else
@ -1758,6 +2168,10 @@ struct aircraft *interactiveCreateAircraft(uint32_t addr) {
a->seen = time(NULL); a->seen = time(NULL);
a->messages = 0; a->messages = 0;
a->squawk = 0; a->squawk = 0;
a->modeACflags = 0;
a->modeAcount = 0;
a->modeCcount = 0;
a->modeC = 0;
a->next = NULL; a->next = NULL;
return a; return a;
} }
@ -1773,6 +2187,48 @@ struct aircraft *interactiveFindAircraft(uint32_t addr) {
} }
return NULL; return NULL;
} }
//
// We have received a Mode A or C response.
//
// Search through the list of known aircraft and tag them if this Mode A/C matches any
// known Mode S Squawks or Altitudes(+/- 50feet).
//
// A Mode S equipped aircraft may also respond to Mode A and Mode C SSR interrogations.
// We can't tell if this is a mode A or C, so scan through the entire aircraft list
// looking for matches on Mode A (squawk) and Mode C (altitude). Flag in the Mode S
// records that we have had a potential Mode A or Mode C response from this aircraft.
//
// If an aircraft responds to Mode A then it's highly likely to be responding to mode C
// too, and vice verca. Therefore, once the mode S record is tagged with both a Mode A
// and a Mode C flag, we can be fairly confident that this Mode A/C frame relates to that
// Mode S aircraft.
//
// Mode C's are more likely to clash than Mode A's; There could be several aircraft
// cruising at FL370, but it's less likely (though not impossible) that there are two
// aircraft on the same squawk. Therefore, give precidence to Mode A record matches
//
void interactiveUpdateAircraftModeA(struct aircraft *a) {
struct aircraft *b = Modes.aircrafts;
while(b) {
if ((b->modeACflags & MODEAC_MSG_FLAG) == 0) {// skip any fudged ICAO records
if (a->squawk == b->squawk) { // If a 'real' Mode S ICAO exists using this Squawk
b->modeAcount++;
if ((b->modeAcount > 0) && (b->modeCcount > 1))
{a->modeACflags |= MODEAC_MSG_MODES_HIT;} // flag that this ModeA/C probably belongs to a known Mode S
} else if ( (a->altitude) // If this ModeC altitude is valid and...
&& (a->modeC == b->modeC) ) // ...a 'real' Mode S ICAO exists at this Altitude
{
b->modeCcount++;
if ((b->modeAcount > 0) && (b->modeCcount > 1))
{a->modeACflags |= MODEAC_MSG_MODES_HIT;} // flag that this ModeA/C probably belongs to a known Mode S
}
}
b = b->next;
}
}
/* Always positive MOD operation, used for CPR decoding. */ /* Always positive MOD operation, used for CPR decoding. */
int cprModFunction(int a, int b) { int cprModFunction(int a, int b) {
@ -1912,11 +2368,11 @@ struct aircraft *interactiveReceiveData(struct modesMessage *mm) {
if (Modes.check_crc && mm->crcok == 0) return NULL; if (Modes.check_crc && mm->crcok == 0) return NULL;
addr = (mm->aa1 << 16) | (mm->aa2 << 8) | mm->aa3; addr = (mm->aa1 << 16) | (mm->aa2 << 8) | mm->aa3;
/* Loookup our aircraft or create a new one. */ // Loookup our aircraft or create a new one
a = interactiveFindAircraft(addr); a = interactiveFindAircraft(addr);
if (!a) { if (!a) { // If it's a currently unknown aircraft....
a = interactiveCreateAircraft(addr); a = interactiveCreateAircraft(addr); // ., create a new record for it,
a->next = Modes.aircrafts; a->next = Modes.aircrafts; // .. and put it at the head of the list
Modes.aircrafts = a; Modes.aircrafts = a;
} else { } else {
/* If it is an already known aircraft, move it on head /* If it is an already known aircraft, move it on head
@ -1942,13 +2398,21 @@ struct aircraft *interactiveReceiveData(struct modesMessage *mm) {
if (mm->msgtype == 0 || mm->msgtype == 4 || mm->msgtype == 20) { if (mm->msgtype == 0 || mm->msgtype == 4 || mm->msgtype == 20) {
a->altitude = mm->altitude; a->altitude = mm->altitude;
a->modeC = mm->modeC;
} else if(mm->msgtype == 5 || mm->msgtype == 21) { } else if(mm->msgtype == 5 || mm->msgtype == 21) {
if (a->squawk != mm->identity) {
a->modeAcount = 0; // Squawk has changed, so zero the hit count
}
a->squawk = mm->identity; a->squawk = mm->identity;
} else if (mm->msgtype == 17) { } else if (mm->msgtype == 17) {
if (mm->metype >= 1 && mm->metype <= 4) { if (mm->metype >= 1 && mm->metype <= 4) {
memcpy(a->flight, mm->flight, sizeof(a->flight)); memcpy(a->flight, mm->flight, sizeof(a->flight));
} else if (mm->metype >= 9 && mm->metype <= 18) { } else if (mm->metype >= 9 && mm->metype <= 18) {
if (a->modeC != mm->modeC) {
a->modeCcount = 0; // Altitude has changed, so zero the hit count
}
a->altitude = mm->altitude; a->altitude = mm->altitude;
a->modeC = mm->modeC;
if (mm->fflag) { if (mm->fflag) {
a->odd_cprlat = mm->raw_latitude; a->odd_cprlat = mm->raw_latitude;
a->odd_cprlon = mm->raw_longitude; a->odd_cprlon = mm->raw_longitude;
@ -1969,6 +2433,14 @@ struct aircraft *interactiveReceiveData(struct modesMessage *mm) {
a->track = mm->heading; a->track = mm->heading;
} }
} }
} else if(mm->msgtype == 32) {
a->modeACflags = MODEAC_MSG_FLAG;
a->squawk = mm->identity;
a->modeC = mm->modeC;
if (mm->altitude > -1300) {
a->altitude = mm->altitude;
}
interactiveUpdateAircraftModeA(a);
} }
return a; return a;
} }
@ -2003,6 +2475,10 @@ void interactiveShowData(void) {
char gs[5] = " "; char gs[5] = " ";
char spacer = '\0'; char spacer = '\0';
if ( ((a->modeACflags & MODEAC_MSG_FLAG) == 0)
|| (((a->modeACflags & MODEAC_MSG_MODES_HIT) == 0) && (altitude == 0) && (msgs > 4))
|| (((a->modeACflags & MODEAC_MSG_MODES_HIT) == 0) && (msgs > 127)) ) {
/* Convert units to metric if --metric was specified. */ /* Convert units to metric if --metric was specified. */
if (Modes.metric) { if (Modes.metric) {
altitude = (int) (altitude / 3.2828); altitude = (int) (altitude / 3.2828);
@ -2019,7 +2495,7 @@ void interactiveShowData(void) {
sprintf(squawk, "%04d", a->squawk); sprintf(squawk, "%04d", a->squawk);
} }
if (a->messages > 99999) { if (msgs > 99999) {
msgs = 99999; msgs = 99999;
} }
@ -2045,9 +2521,10 @@ void interactiveShowData(void) {
a->hexaddr, squawk, a->flight, altitude, speed, a->hexaddr, squawk, a->flight, altitude, speed,
a->lat, a->lon, a->track, msgs, (int)(now - a->seen), spacer); a->lat, a->lon, a->track, msgs, (int)(now - a->seen), spacer);
} }
a = a->next;
count++; count++;
} }
a = a->next;
}
} }
/* When in interactive mode If we don't receive new nessages within /* When in interactive mode If we don't receive new nessages within
@ -2228,7 +2705,7 @@ void modesSendBeastOutput(struct modesMessage *mm) {
{*p++ = '2';} {*p++ = '2';}
else if (msgLen == MODES_LONG_MSG_BYTES) else if (msgLen == MODES_LONG_MSG_BYTES)
{*p++ = '3';} {*p++ = '3';}
else if (msgLen == MODEA_MSG_BYTES) else if (msgLen == MODEAC_MSG_BYTES)
{*p++ = '1';} {*p++ = '1';}
else else
{return;} {return;}
@ -2682,6 +3159,7 @@ void showHelp(void) {
"--interactive-rtl1090 Display flight table in RTL1090 format\n" "--interactive-rtl1090 Display flight table in RTL1090 format\n"
"--raw Show only messages hex values\n" "--raw Show only messages hex values\n"
"--net Enable networking\n" "--net Enable networking\n"
"--modeac Enable decoding of SSR Modes 3/A & 3/C\n"
"--net-beast TCP raw output in Beast binary format\n" "--net-beast TCP raw output in Beast binary format\n"
"--net-only Enable just networking, no RTL device or file used\n" "--net-only Enable just networking, no RTL device or file used\n"
"--net-ro-size <size> TCP raw output minimum size (default: 0)\n" "--net-ro-size <size> TCP raw output minimum size (default: 0)\n"
@ -2720,17 +3198,14 @@ void backgroundTasks(void) {
if (Modes.net) { if (Modes.net) {
modesAcceptClients(); modesAcceptClients();
modesReadFromClients(); modesReadFromClients();
interactiveRemoveStaleAircrafts();
} }
/* Refresh screen when in interactive mode. */ if ( (Modes.aircrafts) && ((mstime() - Modes.interactive_last_update) > MODES_INTERACTIVE_REFRESH_TIME)) {
if (Modes.interactive &&
(mstime() - Modes.interactive_last_update) >
MODES_INTERACTIVE_REFRESH_TIME)
{
interactiveRemoveStaleAircrafts(); interactiveRemoveStaleAircrafts();
interactiveShowData();
Modes.interactive_last_update = mstime(); Modes.interactive_last_update = mstime();
// Refresh screen when in interactive mode
if (Modes.interactive)
{interactiveShowData();}
} }
} }
@ -2762,6 +3237,8 @@ int main(int argc, char **argv) {
Modes.raw = 1; Modes.raw = 1;
} else if (!strcmp(argv[j],"--net")) { } else if (!strcmp(argv[j],"--net")) {
Modes.net = 1; Modes.net = 1;
} else if (!strcmp(argv[j],"--modeac")) {
Modes.mode_ac = 1;
} else if (!strcmp(argv[j],"--net-beast")) { } else if (!strcmp(argv[j],"--net-beast")) {
Modes.beast = 1; Modes.beast = 1;
} else if (!strcmp(argv[j],"--net-only")) { } else if (!strcmp(argv[j],"--net-only")) {
@ -2889,6 +3366,7 @@ int main(int argc, char **argv) {
/* If --ifile and --stats were given, print statistics. */ /* If --ifile and --stats were given, print statistics. */
if (Modes.stats && Modes.filename) { if (Modes.stats && Modes.filename) {
printf("%d ModeA/C detected\n", Modes.stat_ModeAC);
printf("%d valid preambles\n", Modes.stat_valid_preamble); printf("%d valid preambles\n", Modes.stat_valid_preamble);
printf("%d DF-?? fields corrected for length\n", Modes.stat_DF_Corrected); printf("%d DF-?? fields corrected for length\n", Modes.stat_DF_Corrected);
printf("%d demodulated again after phase correction\n", Modes.stat_out_of_phase); printf("%d demodulated again after phase correction\n", Modes.stat_out_of_phase);