refactor how the P25 tx hang (tail) was handled, do not transmit sync…

… instead transmit silence;

Defines.h

@@ -108,10 +108,10 @@ typedef unsigned long long  ulong64_t;
 #define ENABLE_P25
 
 // Normal Boxcar Filter for P25
-#define P25_RX_NORMAL_BOXCAR
+//#define P25_RX_NORMAL_BOXCAR
 
 // Narrow Boxcar Filter for P25
-//#define P25_RX_NARROW_BOXCAR
+#define P25_RX_NARROW_BOXCAR
 
 // Allow for the use of high quality external clock oscillators
 // The number is the frequency of the oscillator in Hertz.

p25/P25TX.cpp

@@ -80,6 +80,7 @@ P25TX::P25TX() :
     m_poLen(0U),
     m_poPtr(0U),
     m_preambleCnt(P25_FIXED_DELAY),
+    m_txHang(P25_FIXED_TX_HANG),
     m_tailCnt(0U),
     m_symLevel3Adj(0U),
     m_symLevel1Adj(0U)
@@ -108,7 +109,7 @@ void P25TX::process()
         uint16_t space = io.getSpace();
 
         while (space > (4U * P25_RADIO_SYMBOL_LENGTH)) {
-            writeByte(P25_START_SYNC);
+            writeSilence();
 
             space -= 4U * P25_RADIO_SYMBOL_LENGTH;
             m_tailCnt--;
@@ -153,7 +154,7 @@ void P25TX::process()
             writeByte(c);
 
             space -= 4U * P25_RADIO_SYMBOL_LENGTH;
-            m_tailCnt = P25_FIXED_TAIL;
+            m_tailCnt = m_txHang;
 
             if (m_poPtr >= m_poLen) {
                 m_poPtr = 0U;
@@ -203,14 +204,29 @@ void P25TX::clear()
 /// <param name="preambleCnt">Count of preambles.</param>
 void P25TX::setPreambleCount(uint8_t preambleCnt)
 {
-    uint32_t preambles = (uint32_t)((float)preambleCnt / 0.2083F);
-    m_preambleCnt = P25_FIXED_DELAY + preambles;
+    m_preambleCnt = P25_FIXED_DELAY + preambleCnt;
 
     // clamp preamble count to 250ms maximum
     if (m_preambleCnt > 1200U)
         m_preambleCnt = 1200U;
 }
 
+/// <summary>
+/// Sets the Tx hang time.
+/// </summary>
+/// <param name="txHang">Transmit hang time in seconds.</param>
+void P25TX::setTxHang(uint8_t txHang)
+{
+    if (txHang > 0U)
+        m_txHang = txHang * 1200U;
+    else
+        m_txHang = P25_FIXED_TX_HANG;
+
+    // clamp tx hang count to 13s maximum
+    if (txHang > 13U)
+        m_txHang = 13U * 1200U;
+}
+
 /// <summary>
 /// Sets the fine adjust 4FSK symbol levels.
 /// </summary>

p25/P25TX.h

@@ -11,7 +11,7 @@
 // Licensed under the GPLv2 License (https://opensource.org/licenses/GPL-2.0)
 //
 /*
-*   Copyright (C) 2016,2017 by Jonathan Naylor G4KLX
+*   Copyright (C) 2016,2017,2020 by Jonathan Naylor G4KLX
 *   Copyright (C) 2020 by Bryan Biedenkapp N2PLL
 *
 *   This program is free software; you can redistribute it and/or modify
@@ -40,9 +40,8 @@ namespace p25
     //  Constants
     // ---------------------------------------------------------------------------
 
-    #define P25_FIXED_DELAY 300     // 300 = 62.49ms
-                                    // Delay Value * 0.2083 = Preamble Length (ms)
-    #define P25_FIXED_TAIL 600      // 600 = 500ms
+    #define P25_FIXED_DELAY 90      // 90 = 20ms
+    #define P25_FIXED_TX_HANG 750   // 750 = 625ms
 
     enum P25TXSTATE {
         P25TXSTATE_NORMAL,
@@ -70,6 +69,8 @@ namespace p25
 
         /// <summary>Sets the FDMA preamble count.</summary>
         void setPreambleCount(uint8_t preambleCnt);
+        /// <summary>Sets the transmit hang time.</summary>
+        void setTxHang(uint8_t txHang);
         /// <summary>Sets the fine adjust 4FSK symbol levels.</summary>
         void setSymbolLvlAdj(int8_t level3Adj, int8_t level1Adj);
         /// <summary>Helper to set the calibration state for Tx.</summary>
@@ -94,6 +95,7 @@ namespace p25
         uint16_t m_poPtr;
 
         uint16_t m_preambleCnt;
+        uint16_t m_txHang;
         uint16_t m_tailCnt;
 
         int8_t m_symLevel3Adj;