From 4cb17c194c72f04c8f4e27b2433d4a1a519f4622 Mon Sep 17 00:00:00 2001
From: Oliver Jowett <oliver@mutability.co.uk>
Date: Tue, 11 Oct 2016 21:29:39 +0100
Subject: [PATCH] More tweaking to A/C tracking.

---
 interactive.c |  6 +++---
 track.c       | 52 ++++++++++++++++++++++++++++++++++++++++-----------
 track.h       |  3 ++-
 3 files changed, 46 insertions(+), 15 deletions(-)

diff --git a/interactive.c b/interactive.c
index c26800b..7be904a 100644
--- a/interactive.c
+++ b/interactive.c
@@ -178,7 +178,7 @@ void interactiveShowData(void) {
 
     if (Modes.mode_ac) {
         for (unsigned i = 1; i < 4096 && row < rows; ++i) {
-            if (modeAC_match[i] || modeAC_count[i] < 100)
+            if (modeAC_match[i] || modeAC_count[i] < 50 || modeAC_age[i] > 5)
                 continue;
 
             char strMode[5] = "  A ";
@@ -191,7 +191,7 @@ void interactiveShowData(void) {
             }
 
             mvprintw(row, 0,
-                     "%7s %-4s  %04x  %-8s %6s %3s  %3s  %7s %8s %5s %5d %2s\n",
+                     "%7s %-4s  %04x  %-8s %6s %3s  %3s  %7s %8s %5s %5d %2d\n",
                      "",    /* address */
                      strMode, /* mode */
                      modeA, /* squawk */
@@ -203,7 +203,7 @@ void interactiveShowData(void) {
                      "",    /* lon */
                      "",    /* signal */
                      modeAC_count[i], /* messages */
-                     "");    /* seen */
+                     modeAC_age[i]);  /* age */
             ++row;
         }
     }
diff --git a/track.c b/track.c
index 12e1c61..1aded30 100644
--- a/track.c
+++ b/track.c
@@ -55,6 +55,7 @@
 uint32_t modeAC_count[4096];
 uint32_t modeAC_lastcount[4096];
 uint32_t modeAC_match[4096];
+uint32_t modeAC_age[4096];
 
 //
 // Return a new aircraft structure for the linked list of tracked
@@ -661,33 +662,62 @@ static void trackMatchAC(uint64_t now)
         // match on Mode A
         if (trackDataValid(&a->squawk_valid)) {
             unsigned i = modeAToIndex(a->squawk);
-            if ((modeAC_count[i] - modeAC_lastcount[i]) > TRACK_MODEAC_MIN_MESSAGES) {
+            if ((modeAC_count[i] - modeAC_lastcount[i]) >= TRACK_MODEAC_MIN_MESSAGES) {
                 a->modeA_hit = 1;
                 modeAC_match[i] = (modeAC_match[i] ? 0xFFFFFFFF : a->addr);
             }
         }
 
-        // match on Mode C
+        // match on Mode C (+/- 100ft)
         if (trackDataValid(&a->altitude_valid)) {
             int modeC = (a->altitude + 49) / 100;
+
             unsigned modeA = modeCToModeA(modeC);
-            if (modeA) {
-                unsigned i = modeAToIndex(modeA);
-                if ((modeAC_count[i] - modeAC_lastcount[i]) > TRACK_MODEAC_MIN_MESSAGES) {
-                    a->modeC_hit = 1;
-                    modeAC_match[i] = (modeAC_match[i] ? 0xFFFFFFFF : a->addr);
-                }
+            unsigned i = modeAToIndex(modeA);
+            if (modeA && (modeAC_count[i] - modeAC_lastcount[i]) >= TRACK_MODEAC_MIN_MESSAGES) {
+                a->modeC_hit = 1;
+                modeAC_match[i] = (modeAC_match[i] ? 0xFFFFFFFF : a->addr);
+            }
+
+            modeA = modeCToModeA(modeC + 1);
+            i = modeAToIndex(modeA);
+            if (modeA && (modeAC_count[i] - modeAC_lastcount[i]) >= TRACK_MODEAC_MIN_MESSAGES) {
+                a->modeC_hit = 1;
+                modeAC_match[i] = (modeAC_match[i] ? 0xFFFFFFFF : a->addr);
+            }
+
+            modeA = modeCToModeA(modeC - 1);
+            i = modeAToIndex(modeA);
+            if (modeA && (modeAC_count[i] - modeAC_lastcount[i]) >= TRACK_MODEAC_MIN_MESSAGES) {
+                a->modeC_hit = 1;
+                modeAC_match[i] = (modeAC_match[i] ? 0xFFFFFFFF : a->addr);
             }
         }
     }
 
     // reset counts for next time
     for (unsigned i = 0; i < 4096; ++i) {
-        if ((modeAC_count[i] - modeAC_lastcount[i]) <= TRACK_MODEAC_MIN_MESSAGES) {
-            modeAC_lastcount[i] = modeAC_count[i] = 0;
+        if (!modeAC_count[i])
+            continue;
+
+        if ((modeAC_count[i] - modeAC_lastcount[i]) < TRACK_MODEAC_MIN_MESSAGES) {
+            if (++modeAC_age[i] > 15) {
+                // not heard from for a while, clear it out
+                modeAC_lastcount[i] = modeAC_count[i] = modeAC_age[i] = 0;
+            }
         } else {
-            modeAC_lastcount[i] = modeAC_count[i];
+            // this one is live
+            // set a high initial age for matches, so they age out rapidly
+            // and don't show up on the interactive display when the matching
+            // mode S data goes away or changes
+            if (modeAC_match[i]) {
+                modeAC_age[i] = 10;
+            } else {
+                modeAC_age[i] = 0;
+            }
         }
+
+        modeAC_lastcount[i] = modeAC_count[i];
     }
 }
 
diff --git a/track.h b/track.h
index 1ce3ae4..de26f68 100644
--- a/track.h
+++ b/track.h
@@ -62,7 +62,7 @@
 /* Minimum number of repeated Mode A/C replies with a particular Mode A code needed in a
  * 1 second period before accepting that code.
  */
-#define TRACK_MODEAC_MIN_MESSAGES 3
+#define TRACK_MODEAC_MIN_MESSAGES 4
 
 typedef struct {
     datasource_t source;     /* where the data came from */
@@ -168,6 +168,7 @@ struct aircraft {
  */
 extern uint32_t modeAC_count[4096];
 extern uint32_t modeAC_match[4096];
+extern uint32_t modeAC_age[4096];
 
 /* is this bit of data valid? */
 static inline int trackDataValid(const data_validity *v)