Decoder cleanups from experimental branch.

demod_2000.c

@@ -317,6 +317,7 @@ void demodulate2000(uint16_t *m, uint32_t mlen) {
         int msglen, scanlen;
         uint32_t sigLevel, noiseLevel;
         uint16_t snr;
+        int message_ok;
 
         pPreamble = &m[j];
         pPayload  = &m[j+MODES_PREAMBLE_SAMPLES];
@@ -325,7 +326,6 @@ void demodulate2000(uint16_t *m, uint32_t mlen) {
         // is required for every bit of the input stream, and we don't want to be memset-ing the whole
         // modesMessage structure two million times per second if we don't have to..
         mm.bFlags          =
-        mm.crcok           = 
         mm.correctedbits   = 0;
 
         if (!use_correction)  // This is not a re-try with phase correction
@@ -544,7 +544,7 @@ void demodulate2000(uint16_t *m, uint32_t mlen) {
             mm.phase_corrected = use_correction;
 
             // Decode the received message
-            decodeModesMessage(&mm, msg);
+            message_ok = (decodeModesMessage(&mm, msg) >= 0);
 
             // Update statistics
             if (Modes.stats) {
@@ -557,16 +557,16 @@ void demodulate2000(uint16_t *m, uint32_t mlen) {
                 default: dstats->demodulated3++; break;
                 }
                 
-                if (mm.crcok) {
+                if (!message_ok) {
+                    dstats->badcrc++;
+                } else if (mm.correctedbits == 0) {
                     dstats->goodcrc++;
                     dstats->goodcrc_byphase[0]++;
-                } else if (mm.correctedbits > 0) {
+                } else {
                     dstats->badcrc++;                    
                     dstats->fixed++;
                     if (mm.correctedbits <= MODES_MAX_BITERRORS)
                         dstats->bit_fix[mm.correctedbits-1] += 1;
-                } else {
-                    dstats->badcrc++;
                 }
             }
 
@@ -576,22 +576,23 @@ void demodulate2000(uint16_t *m, uint32_t mlen) {
                     dumpRawMessage("Demodulated with 0 errors", msg, m, j);
                 else if (Modes.debug & MODES_DEBUG_BADCRC &&
                          mm.msgtype == 17 &&
-                         (!mm.crcok || mm.correctedbits != 0))
+                         (!message_ok || mm.correctedbits > 0))
                     dumpRawMessage("Decoded with bad CRC", msg, m, j);
-                else if (Modes.debug & MODES_DEBUG_GOODCRC && mm.crcok &&
+                else if (Modes.debug & MODES_DEBUG_GOODCRC &&
+                         message_ok && 
                          mm.correctedbits == 0)
                     dumpRawMessage("Decoded with good CRC", msg, m, j);
             }
 
             // Skip this message if we are sure it's fine
-            if (mm.crcok || mm.correctedbits) {
+            if (message_ok) {
                 j += (MODES_PREAMBLE_US+msglen)*2 - 1;
+
+                // Pass data to the next layer
+                useModesMessage(&mm);
             }
-
-            // Pass data to the next layer
-            useModesMessage(&mm);
-
         } else {
+            message_ok = 0;
             if (Modes.debug & MODES_DEBUG_DEMODERR && use_correction) {
                 printf("The following message has %d demod errors\n", errors);
                 dumpRawMessage("Demodulated with errors", msg, m, j);
@@ -599,7 +600,7 @@ void demodulate2000(uint16_t *m, uint32_t mlen) {
         }
 
         // Retry with phase correction if enabled, necessary and possible.
-        if (Modes.phase_enhance && !mm.crcok && !mm.correctedbits && !use_correction && j && detectOutOfPhase(pPreamble)) {
+        if (Modes.phase_enhance && (!message_ok || mm.correctedbits > 0) && !use_correction && j && detectOutOfPhase(pPreamble)) {
             use_correction = 1; j--;
         } else {
             use_correction = 0; 

demod_2400.c

@@ -273,7 +273,6 @@ void demodulate2400(uint16_t *m, uint32_t mlen)
         // is required for every possible preamble, and we don't want to be memset-ing the whole
         // modesMessage structure if we don't have to..
         mm.bFlags          =
-            mm.crcok           = 
             mm.correctedbits   = 0;
 
         // Decode all the next 112 bits, regardless of the actual message
@@ -456,13 +455,15 @@ void demodulate2400(uint16_t *m, uint32_t mlen)
         if ( (msglen) 
              // && ((2 * snr) > (int) (MODES_MSG_SQUELCH_DB * 10))
           && (errors      <= MODES_MSG_ENCODER_ERRS) ) {
+            int message_ok;
+
             // Set initial mm structure details
             mm.timestampMsg = Modes.timestampBlk + (j*5) + try_phase;
             mm.signalLevel = (snr > 255 ? 255 : (uint8_t)snr);
             mm.phase_corrected = (initial_phase != try_phase);
             
             // Decode the received message
-            decodeModesMessage(&mm, msg);
+            message_ok = (decodeModesMessage(&mm, msg) >= 0);
 
             // Update statistics
             if (Modes.stats) {
@@ -475,16 +476,16 @@ void demodulate2400(uint16_t *m, uint32_t mlen)
                 default: dstats->demodulated3++; break;
                 }
                 
-                if (mm.crcok) {
+                if (!message_ok) {
-                    dstats->goodcrc++;
+                    dstats->badcrc++;
-                    dstats->goodcrc_byphase[try_phase%MODES_MAX_PHASE_STATS]++;
                 } else if (mm.correctedbits > 0) {
                     dstats->badcrc++;                    
                     dstats->fixed++;
                     if (mm.correctedbits <= MODES_MAX_BITERRORS)
                         dstats->bit_fix[mm.correctedbits-1] += 1;
                 } else {
-                    dstats->badcrc++;
+                    dstats->goodcrc++;
+                    dstats->goodcrc_byphase[try_phase%MODES_MAX_PHASE_STATS]++;
                 }
             }
             
@@ -494,7 +495,7 @@ void demodulate2400(uint16_t *m, uint32_t mlen)
             //  where the preamble of the second message clobbered the last
             //  few bits of the first message, but the message bits didn't
             //  overlap)
-            if (mm.crcok || mm.correctedbits) {
+            if (message_ok) {
                 j += (8 + msglen - 8)*12/5 - 1;
             }
             
@@ -506,7 +507,7 @@ void demodulate2400(uint16_t *m, uint32_t mlen)
             // where trying different phases actually helps, and is much
             // cheaper than trying it on every single candidate that passes
             // peak detection
-            if (Modes.phase_enhance && !mm.crcok && !mm.correctedbits) {
+            if (Modes.phase_enhance && !message_ok) {
                 if (try_phase == initial_phase)
                     ++Modes.stats_current.out_of_phase;
                 try_phase++;

dump1090.h

@@ -406,7 +406,6 @@ struct modesMessage {
     unsigned char msg[MODES_LONG_MSG_BYTES];      // Binary message.
     int           msgbits;                        // Number of bits in message 
     int           msgtype;                        // Downlink format #
-    int           crcok;                          // True if CRC was valid
     uint32_t      crc;                            // Message CRC
     int           correctedbits;                  // No. of bits corrected 
     char          corrected[MODES_MAX_BITERRORS]; // corrected bit positions
@@ -416,7 +415,7 @@ struct modesMessage {
     int           remote;                         // If set this message is from a remote station
     unsigned char signalLevel;                    // Signal Amplitude
 
-    // DF 11
+    // DF 11, DF 17
     int  ca;                    // Responder capabilities
     int  iid;
 
@@ -434,10 +433,16 @@ struct modesMessage {
     int    vert_rate;           // Vertical rate.
     int    velocity;            // Reported by aircraft, or computed from from EW and NS velocity
 
+    // DF 18
+    int    cf;                  // Control Field
+
     // DF4, DF5, DF20, DF21
     int  fs;                    // Flight status for DF4,5,20,21
     int  modeA;                 // 13 bits identity (Squawk).
 
+    // DF20, DF21
+    int  bds;                   // BDS value implied if overlay control was used
+
     // Fields used by multiple message types.
     int  altitude;
     int  unit; 
@@ -462,7 +467,7 @@ int  ModeAToModeC      (unsigned int ModeA);
 //
 int modesMessageLenByType(int type);
 void detectModeS_oversample (uint16_t *m, uint32_t mlen);
-void decodeModesMessage (struct modesMessage *mm, unsigned char *msg);
+int decodeModesMessage (struct modesMessage *mm, unsigned char *msg);
 void displayModesMessage(struct modesMessage *mm);
 void useModesMessage    (struct modesMessage *mm);
 void computeMagnitudeVector(uint16_t *pData);

icao_filter.c

@@ -26,7 +26,7 @@
 #define MODES_ICAO_FILTER_TTL 60
 
 // Open-addressed hash table with linear probing.
-// We store each address twice to handle Address/Parity and Data/Parity
+// We store each address twice to handle Data/Parity
 // which need to match on a partial address (top 16 bits only).
 
 // Maintain two tables and switch between them to age out entries.

interactive.c

@@ -380,13 +380,7 @@ static void updatePosition(struct aircraft *a, struct modesMessage *mm, time_t n
 
 struct aircraft *interactiveReceiveData(struct modesMessage *mm) {
     struct aircraft *a, *aux;
-    time_t now;
+    time_t now = time(NULL);
-
-    // Return if (checking crc) AND (not crcok) AND (not fixed)
-    if (Modes.check_crc && (mm->crcok == 0) && (mm->correctedbits == 0))
-        return NULL;
-
-    now = time(NULL);
 
     // Lookup our aircraft or create a new one
     a = interactiveFindAircraft(mm->addr);

mode_ac.c

@@ -385,7 +385,6 @@ void decodeModeAMessage(struct modesMessage *mm, int ModeA)
 
   // 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->correctedbits = 0;
   }
 //

net_io.c

@@ -579,7 +579,12 @@ int decodeBinMessage(struct client *c, char *p) {
         if (msgLen == MODEAC_MSG_BYTES) { // ModeA or ModeC
             decodeModeAMessage(&mm, ((msg[0] << 8) | msg[1]));
         } else {
-            decodeModesMessage(&mm, msg);
+            if (decodeModesMessage(&mm, msg) < 0) {
+                Modes.stats_current.remote_rejected++;
+                return 0;
+            } else {
+                Modes.stats_current.remote_accepted++;
+            }
         }
 
         useModesMessage(&mm);
@@ -678,7 +683,12 @@ int decodeHexMessage(struct client *c, char *hex) {
     if (l == (MODEAC_MSG_BYTES * 2)) {  // ModeA or ModeC
         decodeModeAMessage(&mm, ((msg[0] << 8) | msg[1]));
     } else {       // Assume ModeS
-        decodeModesMessage(&mm, msg);
+        if (decodeModesMessage(&mm, msg) < 0) {
+            Modes.stats_current.remote_rejected++;
+            return 0;
+        } else {
+            Modes.stats_current.remote_accepted++;
+        }
     }
 
     useModesMessage(&mm);