From 04ca97e5f81371175ea7013a8610e7beb63ff7a8 Mon Sep 17 00:00:00 2001
From: Jonathan Naylor <naylorjs@yahoo.com>
Date: Sun, 13 Aug 2017 18:51:09 +0100
Subject: [PATCH] Add enhancements suggested by IZ1MLT.

---
 DStarRX.cpp | 32 ++++++++++----------------------
 1 file changed, 10 insertions(+), 22 deletions(-)

diff --git a/DStarRX.cpp b/DStarRX.cpp
index c55edd5..4f65f6f 100644
--- a/DStarRX.cpp
+++ b/DStarRX.cpp
@@ -28,11 +28,7 @@ const uint32_t PLLMAX = 0x10000U;
 const uint32_t PLLINC = PLLMAX / DSTAR_RADIO_BIT_LENGTH;
 const uint32_t INC    = PLLINC / 32U;
 
-const unsigned int MAX_SYNC_BITS = 50U * DSTAR_DATA_LENGTH_BITS;
-
-const unsigned int SYNC_POS        = 21U * DSTAR_DATA_LENGTH_BITS;
-const unsigned int SYNC_SCAN_START = SYNC_POS - 3U;
-const unsigned int SYNC_SCAN_END   = SYNC_POS + 3U;
+const unsigned int MAX_SYNC_BITS = 100U * DSTAR_DATA_LENGTH_BITS;
 
 // D-Star bit order version of 0x55 0x55 0x6E 0x0A
 const uint32_t FRAME_SYNC_DATA = 0x00557650U;
@@ -372,7 +368,7 @@ void CDStarRX::processNone(bool bit)
     ::memset(m_rxBuffer, 0x00U, DSTAR_DATA_LENGTH_BYTES + 2U);
     m_rxBufferBits = 0U;
 
-    m_dataBits  = 0U;
+    m_dataBits  = MAX_SYNC_BITS;
     m_rxState   = DSRXS_DATA;
     return;
   }
@@ -401,8 +397,8 @@ void CDStarRX::processHeader(bool bit)
       ::memset(m_rxBuffer, 0x00U, DSTAR_DATA_LENGTH_BYTES + 2U);
       m_rxBufferBits = 0U;
 
-      m_rxState   = DSRXS_DATA;
-      m_dataBits  = SYNC_POS - DSTAR_DATA_LENGTH_BITS + 1U;
+      m_rxState  = DSRXS_DATA;
+      m_dataBits = MAX_SYNC_BITS;
     } else {
       // The checksum failed, return to looking for syncs
       m_rxState = DSRXS_NONE;
@@ -434,37 +430,29 @@ void CDStarRX::processData(bool bit)
 
   // Fuzzy matching of the data sync bit sequence
   bool syncSeen = false;
-  if (m_dataBits >= SYNC_SCAN_START && m_dataBits <= (SYNC_POS + 1U)) {
+  if (m_rxBufferBits >= (DSTAR_DATA_LENGTH_BITS - 3U)) {
     if (countBits32((m_patternBuffer & DATA_SYNC_MASK) ^ DATA_SYNC_DATA) <= DATA_SYNC_ERRS) {
-      if (m_dataBits < SYNC_POS)
-        DEBUG2("DStarRX: found data sync in Data, early", SYNC_POS - m_dataBits);
-      else
-        DEBUG1("DStarRX: found data sync in Data");
-
       m_rxBufferBits = DSTAR_DATA_LENGTH_BITS;
-      m_dataBits = 0U;
-      syncSeen   = true;
+      m_dataBits     = MAX_SYNC_BITS;
+      syncSeen       = true;
     }
   }
 
   // Check to see if the sync is arriving late
-  if (m_dataBits == SYNC_POS) {
+  if (m_rxBufferBits == DSTAR_DATA_LENGTH_BITS && !syncSeen) {
     for (uint8_t i = 1U; i <= 3U; i++) {
       uint32_t syncMask = DATA_SYNC_MASK >> i;
       uint32_t syncData = DATA_SYNC_DATA >> i;
       if (countBits32((m_patternBuffer & syncMask) ^ syncData) <= DATA_SYNC_ERRS) {
-        DEBUG2("DStarRX: found data sync in Data, late", i);
         m_rxBufferBits -= i;
-        m_dataBits     -= i;
         break;
       }
     }
   }
 
-  m_dataBits++;
+  m_dataBits--;
 
-  // We've not seen a data sync for too long, signal RXLOST and change to RX_NONE
-  if (m_dataBits >= MAX_SYNC_BITS) {
+  if (m_dataBits == 0U) {
     DEBUG1("DStarRX: data sync timed out, lost lock");
 
     io.setDecode(false);