Add transmit hangs to NXDN and P25.

NXDNTX.h

@@ -1,5 +1,5 @@
 /*
- *   Copyright (C) 2015,2016,2017,2018 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2015,2016,2017,2018,2020 by Jonathan Naylor G4KLX
  *
  *   This program is free software; you can redistribute it and/or modify
  *   it under the terms of the GNU General Public License as published by
@@ -35,6 +35,8 @@ public:
 
   uint8_t getSpace() const;
 
+  void setParams(uint8_t txHang);
+
 private:
   CSerialRB                        m_buffer;
   arm_fir_interpolate_instance_q15 m_modFilter;
@@ -45,9 +47,11 @@ private:
   uint16_t                         m_poLen;
   uint16_t                         m_poPtr;
   uint16_t                         m_txDelay;
+  uint32_t                         m_txHang;
+  uint32_t                         m_txCount;
 
   void writeByte(uint8_t c);
+  void writeSilence();
 };
 
 #endif
-