From e4d135849aac21d4def990ee37c780b2a752b843 Mon Sep 17 00:00:00 2001
From: Bryan Biedenkapp <gatekeep@gmail.com>
Date: Fri, 12 Aug 2022 23:27:14 -0400
Subject: [PATCH] code cleanup; properly apply RCCH post field after scrambler;

---
 nxdn/NXDNDefines.h    |  4 ++--
 nxdn/channel/CAC.cpp  |  9 +--------
 nxdn/packet/Trunk.cpp | 24 +++++++++++++++++++++++-
 nxdn/packet/Trunk.h   |  3 +++
 4 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/nxdn/NXDNDefines.h b/nxdn/NXDNDefines.h
index d0bb0032..d7b03b41 100644
--- a/nxdn/NXDNDefines.h
+++ b/nxdn/NXDNDefines.h
@@ -77,6 +77,8 @@ namespace nxdn
     const uint8_t   NXDN_FSW_BYTES_MASK[] = { 0xFFU, 0xFFU, 0xF0U };
     const uint32_t  NXDN_FSW_BYTES_LENGTH = 3U;
 
+    const uint8_t   NXDN_PREAMBLE[] = { 0x57U, 0x75U, 0xFDU };
+
     const uint32_t  NXDN_LICH_LENGTH_BITS = 16U;
     const uint32_t  NXDN_LICH_LENGTH_BYTES = NXDN_LICH_LENGTH_BITS / 8U;
 
@@ -130,8 +132,6 @@ namespace nxdn
     const uint32_t  NXDN_RCCH_CAC_LC_LONG_LENGTH_BITS = 128U;
     const uint32_t  NXDN_RCCH_CAC_LC_SHORT_LENGTH_BITS = 96U;
 
-    const uint8_t   POST_FIELD[] = { 0x57U, 0x75U, 0xFDU };
-
     const uint32_t  NXDN_FSW_LICH_SACCH_LENGTH_BITS  = NXDN_FSW_LENGTH_BITS + NXDN_LICH_LENGTH_BITS + NXDN_SACCH_LENGTH_BITS;
     const uint32_t  NXDN_FSW_LICH_SACCH_LENGTH_BYTES = NXDN_FSW_LICH_SACCH_LENGTH_BITS / 8U;
 
diff --git a/nxdn/channel/CAC.cpp b/nxdn/channel/CAC.cpp
index f1f3f2be..a7e3467c 100644
--- a/nxdn/channel/CAC.cpp
+++ b/nxdn/channel/CAC.cpp
@@ -339,15 +339,8 @@ void CAC::encode(uint8_t* data) const
         WRITE_BIT(data, n, b);
     }
 
-    // post field
-    for (uint32_t i = 0U; i < NXDN_CAC_E_POST_FIELD_BITS; i++) {
-        uint32_t n = i + NXDN_FSW_LENGTH_BITS + NXDN_LICH_LENGTH_BITS + NXDN_CAC_FEC_LENGTH_BITS + NXDN_CAC_E_POST_FIELD_BITS;
-        bool b = READ_BIT(POST_FIELD, i);
-        WRITE_BIT(data, n, b);
-    }
-
 #if DEBUG_NXDN_CAC
-    Utils::dump(2U, "CAC::encode(), CAC + E + Post", data, NXDN_FRAME_LENGTH_BYTES);
+    Utils::dump(2U, "CAC::encode(), CAC + Control", data, NXDN_FRAME_LENGTH_BYTES);
 #endif
 }
 
diff --git a/nxdn/packet/Trunk.cpp b/nxdn/packet/Trunk.cpp
index 877d944c..d62175ba 100644
--- a/nxdn/packet/Trunk.cpp
+++ b/nxdn/packet/Trunk.cpp
@@ -410,6 +410,8 @@ void Trunk::writeRF_Message(bool noNetwork, bool clearBeforeWrite)
 
     m_nxdn->scrambler(data + 2U);
 
+    addPostBits(data + 2U);
+
     if (!noNetwork)
         writeNetwork(data, NXDN_FRAME_LENGTH_BYTES + 2U);
 
@@ -706,7 +708,7 @@ void Trunk::writeRF_CC_Message_Site_Info()
     channel::CAC cac;
     cac.setVerbose(m_dumpRCCH);
     cac.setRAN(m_nxdn->m_ran);
-    cac.setStructure(NXDN_SR_RCCH_HEAD_SINGLE);
+    cac.setStructure(NXDN_SR_RCCH_SINGLE);
     cac.setData(buffer);
     cac.encode(data + 2U);
 
@@ -715,6 +717,8 @@ void Trunk::writeRF_CC_Message_Site_Info()
 
     m_nxdn->scrambler(data + 2U);
 
+    addPostBits(data + 2U);
+
     if (m_nxdn->m_duplex) {
         m_nxdn->addFrame(data, NXDN_FRAME_LENGTH_BYTES + 2U);
     }
@@ -762,7 +766,25 @@ void Trunk::writeRF_CC_Message_Service_Info()
 
     m_nxdn->scrambler(data + 2U);
 
+    addPostBits(data + 2U);
+
     if (m_nxdn->m_duplex) {
         m_nxdn->addFrame(data, NXDN_FRAME_LENGTH_BYTES + 2U);
     }
 }
+
+/// <summary>
+/// Helper to add the post field bits on NXDN frame data.
+/// </summary>
+/// <param name="data"></param>
+void Trunk::addPostBits(uint8_t* data)
+{
+    assert(data != NULL);
+
+    // post field
+    for (uint32_t i = 0U; i < NXDN_CAC_E_POST_FIELD_BITS; i++) {
+        uint32_t n = i + NXDN_FSW_LENGTH_BITS + NXDN_LICH_LENGTH_BITS + NXDN_CAC_FEC_LENGTH_BITS + NXDN_CAC_E_POST_FIELD_BITS;
+        bool b = READ_BIT(NXDN_PREAMBLE, i);
+        WRITE_BIT(data, n, b);
+    }
+}
diff --git a/nxdn/packet/Trunk.h b/nxdn/packet/Trunk.h
index 9da7ddd4..6d01cbc2 100644
--- a/nxdn/packet/Trunk.h
+++ b/nxdn/packet/Trunk.h
@@ -118,6 +118,9 @@ namespace nxdn
             void writeRF_CC_Message_Site_Info();
             /// <summary>Helper to write a CC SRV_INFO broadcast packet on the RF interface.</summary>
             void writeRF_CC_Message_Service_Info();
+
+            /// <summary>Helper to add the post field bits on NXDN frame data.</summary>
+            void addPostBits(uint8_t* data);
         };
     } // namespace packet
 } // namespace nxdn