From 2f52282c47207c26f7aad268dd4b6fa946c219cf Mon Sep 17 00:00:00 2001
From: Jonathan Naylor <naylorjs@yahoo.com>
Date: Sat, 2 Jan 2021 12:28:19 +0000
Subject: [PATCH] Clean up the M17 synchronisation.

---
 M17RX.cpp | 38 +++++++++++++-------------------------
 M17RX.h   |  4 ++--
 version.h |  2 +-
 3 files changed, 16 insertions(+), 28 deletions(-)

diff --git a/M17RX.cpp b/M17RX.cpp
index b16ce9a..e3a6696 100644
--- a/M17RX.cpp
+++ b/M17RX.cpp
@@ -25,7 +25,7 @@
 const uint8_t MAX_SYNC_BIT_START_ERRS = 0U;
 const uint8_t MAX_SYNC_BIT_RUN_ERRS   = 2U;
 
-const unsigned int MAX_SYNC_FRAMES = 5U + 1U;
+const unsigned int MAX_SYNC_FRAMES = 3U + 1U;
 
 const uint8_t BIT_MASK_TABLE[] = {0x80U, 0x40U, 0x20U, 0x10U, 0x08U, 0x04U, 0x02U, 0x01U};
 
@@ -53,17 +53,17 @@ void CM17RX::reset()
 void CM17RX::databit(bool bit)
 {
   switch (m_state)  {
-    case M17RXS_NONE:
-      processNone(bit);
+    case M17RXS_LINK_SETUP:
+      processLinkSetup(bit);
       break;
-    case M17RXS_HEADER:
-      processHeader(bit);
+    case M17RXS_STREAM:
+      processStream(bit);
       break;
     case M17RXS_PACKET:
       processPacket(bit);
       break;
     default:
-      processStream(bit);
+      processNone(bit);
       break;
   }
 }
@@ -74,15 +74,15 @@ void CM17RX::processNone(bool bit)
   if (bit)
     m_bitBuffer |= 0x01U;
 
-  // Fuzzy matching of the header sync bit sequence
+  // Fuzzy matching of the link setup sync bit sequence
   if (countBits16(m_bitBuffer ^ M17_LINK_SETUP_SYNC_BITS) <= MAX_SYNC_BIT_START_ERRS) {
-    DEBUG1("M17RX: header sync found in None");
+    DEBUG1("M17RX: link setup sync found in None");
     for (uint8_t i = 0U; i < M17_SYNC_BYTES_LENGTH; i++)
       m_buffer[i] = M17_LINK_SETUP_SYNC_BYTES[i];
 
     m_lostCount = MAX_SYNC_FRAMES;
     m_bufferPtr = M17_SYNC_LENGTH_BITS;
-    m_state     = M17RXS_HEADER;
+    m_state     = M17RXS_LINK_SETUP;
 
     io.setDecode(true);
   }
@@ -114,7 +114,7 @@ void CM17RX::processNone(bool bit)
   }
 }
 
-void CM17RX::processHeader(bool bit)
+void CM17RX::processLinkSetup(bool bit)
 {
   m_bitBuffer <<= 1;
   if (bit)
@@ -126,16 +126,6 @@ void CM17RX::processHeader(bool bit)
   if (m_bufferPtr > M17_FRAME_LENGTH_BITS)
     reset();
 
-  // Only search for a sync in the right place +-2 symbols
-  if (m_bufferPtr >= (M17_SYNC_LENGTH_BITS - 2U) && m_bufferPtr <= (M17_SYNC_LENGTH_BITS + 2U)) {
-    // Fuzzy matching of the data sync bit sequence
-    if (countBits16(m_bitBuffer ^ M17_LINK_SETUP_SYNC_BITS) <= MAX_SYNC_BIT_RUN_ERRS) {
-      DEBUG2("M17RX: found header sync in Data, pos", m_bufferPtr - M17_SYNC_LENGTH_BITS);
-      m_lostCount = MAX_SYNC_FRAMES;
-      m_bufferPtr = M17_SYNC_LENGTH_BITS;
-    }
-  }
-
   // Send a data frame to the host if the required number of bits have been received
   if (m_bufferPtr == M17_FRAME_LENGTH_BITS) {
     m_lostCount--;
@@ -145,9 +135,7 @@ void CM17RX::processHeader(bool bit)
     writeRSSIHeader(m_outBuffer);
 
     // Start the next frame, but we don't know the type
-    ::memset(m_outBuffer, 0x00U, M17_FRAME_LENGTH_BYTES + 3U);
-    m_state     = M17RXS_NONE;
-    m_bufferPtr = 0U;
+    reset();
   }
 }
 
@@ -167,7 +155,7 @@ void CM17RX::processStream(bool bit)
   if (m_bufferPtr >= (M17_SYNC_LENGTH_BITS - 2U) && m_bufferPtr <= (M17_SYNC_LENGTH_BITS + 2U)) {
     // Fuzzy matching of the stream sync bit sequence
     if (countBits16(m_bitBuffer ^ M17_STREAM_SYNC_BITS) <= MAX_SYNC_BIT_RUN_ERRS) {
-      DEBUG2("M17RX: found stream sync in Data, pos", m_bufferPtr - M17_SYNC_LENGTH_BITS);
+      DEBUG2("M17RX: found stream sync, pos", m_bufferPtr - M17_SYNC_LENGTH_BITS);
       m_lostCount = MAX_SYNC_FRAMES;
       m_bufferPtr = M17_SYNC_LENGTH_BITS;
     }
@@ -211,7 +199,7 @@ void CM17RX::processPacket(bool bit)
   if (m_bufferPtr >= (M17_SYNC_LENGTH_BITS - 2U) && m_bufferPtr <= (M17_SYNC_LENGTH_BITS + 2U)) {
     // Fuzzy matching of the packet sync bit sequence
     if (countBits16(m_bitBuffer ^ M17_PACKET_SYNC_BITS) <= MAX_SYNC_BIT_RUN_ERRS) {
-      DEBUG2("M17RX: found packet sync in Data, pos", m_bufferPtr - M17_SYNC_LENGTH_BITS);
+      DEBUG2("M17RX: found packet sync, pos", m_bufferPtr - M17_SYNC_LENGTH_BITS);
       m_lostCount = MAX_SYNC_FRAMES;
       m_bufferPtr = M17_SYNC_LENGTH_BITS;
     }
diff --git a/M17RX.h b/M17RX.h
index 417e5ab..0cf3626 100644
--- a/M17RX.h
+++ b/M17RX.h
@@ -24,7 +24,7 @@
 
 enum M17RX_STATE {
   M17RXS_NONE,
-  M17RXS_HEADER,
+  M17RXS_LINK_SETUP,
   M17RXS_STREAM,
   M17RXS_PACKET
 };
@@ -46,7 +46,7 @@ private:
   uint16_t    m_lostCount;
 
   void processNone(bool bit);
-  void processHeader(bool bit);
+  void processLinkSetup(bool bit);
   void processStream(bool bit);
   void processPacket(bool bit);
   void writeRSSIHeader(uint8_t* data);
diff --git a/version.h b/version.h
index 94c0c84..d48ac89 100644
--- a/version.h
+++ b/version.h
@@ -25,7 +25,7 @@
 #define VER_MAJOR       "1"
 #define VER_MINOR       "5"
 #define VER_REV         "2"
-#define VERSION_DATE    "20210101"
+#define VERSION_DATE    "20210102"
 
 #if defined(ZUMSPOT_ADF7021)
 #define BOARD_INFO      "ZUMspot"