Always use phase enhancement; silently ignore --phase-enhance if given.

debian/config-template

@@ -34,9 +34,6 @@ PPM=
 # If yes, enable sampling at 2.4MHz. Otherwise, 2.0MHz is used.
 OVERSAMPLE=
 
-# If yes, enables phase-enhancement of messages
-PHASE_ENHANCE=
-
 #
 # Decoding options
 #

debian/dump1090-mutability.config

@@ -26,7 +26,6 @@ if [ -e $CONFIGFILE ]; then
   db_set_yn $NAME/rtlsdr-oversample "$OVERSAMPLE"
 
   db_set_yn $NAME/decode-fixcrc "$FIX_CRC"
-  db_set_yn $NAME/decode-phase-enhance "$PHASE_ENHANCE"
   db_set $NAME/decode-lat "$LAT"
   db_set $NAME/decode-lon "$LON"
   db_set $NAME/decode-max-range "$MAX_RANGE"

debian/dump1090-mutability.postinst

@@ -77,7 +77,6 @@ case "$1" in
         subvar rtlsdr-ppm PPM
         subvar_yn rtlsdr-oversample OVERSAMPLE
         subvar_yn decode-fixcrc FIX_CRC
-        subvar_yn decode-phase-enhance PHASE_ENHANCE
         subvar decode-lat LAT
         subvar decode-lon LON
         subvar decode-max-range MAX_RANGE

debian/dump1090-mutability.templates

@@ -69,13 +69,6 @@ Description: Fix detected CRC errors?
 Type: boolean
 Default: true
 
-Template: dump1090-mutability/decode-phase-enhance
-Description: Apply phase enhancement?
- dump1090 can attempt to correct for messages that are received
- out-of-phase from the sampling rate, at the expense of taking more CPU.
-Type: boolean
-Default: true
-
 Template: dump1090-mutability/decode-lat
 Description: Latitude of receiver, in decimal degrees:
  If the location of the receiver is provided, dump1090 can do

demod_2000.c

@@ -880,8 +880,8 @@ void demodulate2000(struct mag_buf *mag) {
             }
         }
 
-        // Retry with phase correction if enabled, necessary and possible.
+        // Retry with phase correction if necessary and possible.
-        if (Modes.phase_enhance && (!message_ok || mm.correctedbits > 0) && !use_correction && j && detectOutOfPhase(pPreamble)) {
+        if ((!message_ok || mm.correctedbits > 0) && !use_correction && j && detectOutOfPhase(pPreamble)) {
             use_correction = 1; j--;
         } else {
             use_correction = 0; 

demod_2400.c

@@ -118,33 +118,6 @@ static inline int correlate_check_4(uint16_t *m) {
         abs(correlate_phase2(&m[10]));
 }
 
-// Work out the best phase offset to use for the given message.
-static int best_phase(uint16_t *m) {
-    int test;
-    int best = -1;
-    int bestval = (m[0] + m[1] + m[2] + m[3] + m[4] + m[5]); // minimum correlation quality we will accept
-
-    // empirical testing suggests that 4..8 is the best range to test for here
-    // (testing a wider range runs the danger of picking the wrong phase for
-    // a message that would otherwise be successfully decoded - the correlation
-    // functions can match well with a one symbol / half bit offset)
-
-    // this is consistent with the peak detection which should produce
-    // the first data symbol with phase offset 4..8
-
-    test = correlate_check_4(&m[0]);
-    if (test > bestval) { bestval = test; best = 4; }
-    test = correlate_check_0(&m[1]);
-    if (test > bestval) { bestval = test; best = 5; }
-    test = correlate_check_1(&m[1]);
-    if (test > bestval) { bestval = test; best = 6; }
-    test = correlate_check_2(&m[1]);
-    if (test > bestval) { bestval = test; best = 7; }
-    test = correlate_check_3(&m[1]);
-    if (test > bestval) { bestval = test; best = 8; }
-    return best;
-}
-
 //
 // Given 'mlen' magnitude samples in 'm', sampled at 2.4MHz,
 // try to demodulate some Mode S messages.
@@ -170,7 +143,7 @@ void demodulate2400(struct mag_buf *mag)
         uint16_t *preamble = &m[j];
         int high;
         uint32_t base_signal, base_noise;
-        int initial_phase, first_phase, last_phase, try_phase;
+        int try_phase;
         int msglen;
 
         // Look for a message starting at around sample 0 with phase offset 3..7
@@ -252,22 +225,10 @@ void demodulate2400(struct mag_buf *mag)
             continue;
         }
 
-        if (Modes.phase_enhance) {
+        // try all phases
-            first_phase = 4;
-            last_phase = 8;           // try all phases
-        } else {
-            // Crosscorrelate against the first few bits to find a likely phase offset
-            initial_phase = best_phase(&preamble[19]);
-            if (initial_phase < 0) {
-                continue; // nothing satisfactory
-            }
-            
-            first_phase = last_phase = initial_phase;  // try only the phase we think it is
-        }
-
         Modes.stats_current.demod_preambles++;
         bestmsg = NULL; bestscore = -2; bestphase = -1;
-        for (try_phase = first_phase; try_phase <= last_phase; ++try_phase) {
+        for (try_phase = 4; try_phase <= 8; ++try_phase) {
             uint16_t *pPtr;
             int phase, i, score, bytelen;
 

dump1090.c

@@ -702,7 +702,6 @@ void showHelp(void) {
 "--fix                    Enable single-bits error correction using CRC\n"
 "--no-fix                 Disable single-bits error correction using CRC\n"
 "--no-crc-check           Disable messages with broken CRC (discouraged)\n"
-"--phase-enhance          Enable phase enhancement\n"
 #ifdef ALLOW_AGGRESSIVE
 "--aggressive             More CPU for more messages (two bits fixes, ...)\n"
 #endif
@@ -964,7 +963,7 @@ int main(int argc, char **argv) {
         } else if (!strcmp(argv[j],"--no-crc-check")) {
             Modes.check_crc = 0;
         } else if (!strcmp(argv[j],"--phase-enhance")) {
-            Modes.phase_enhance = 1;
+            // Ignored, always enabled
         } else if (!strcmp(argv[j],"--raw")) {
             Modes.raw = 1;
         } else if (!strcmp(argv[j],"--net")) {

dump1090.h

@@ -282,7 +282,6 @@ struct {                             // Internal state
     // Configuration
     char *filename;                  // Input form file, --ifile option
     int   oversample;
-    int   phase_enhance;             // Enable phase enhancement if true
     int   nfix_crc;                  // Number of crc bit error(s) to correct
     int   check_crc;                 // Only display messages with good CRC
     int   raw;                       // Raw output format