Add companion terminal mode and LoRa OTA tooling

src/helpers/ArduinoSerialInterface.h

@@ -5,22 +5,46 @@
 
 class ArduinoSerialInterface : public BaseSerialInterface {
   bool _isEnabled;
+  bool _passthroughMode;
+  bool _controlSequenceReceived;
   uint8_t _state;
+  size_t _controlSequencePos;
   uint16_t _frame_len;
   uint16_t rx_len;
   Stream* _serial;
+  const char* _controlSequence;
   uint8_t rx_buf[MAX_FRAME_SIZE];
 
-public:
-  ArduinoSerialInterface() { _isEnabled = false; _state = 0; }
+  bool checkControlSequence(uint8_t c);
+  void resetReceiveState();
 
-  void begin(Stream& serial) { 
-    _serial = &serial; 
+public:
+  ArduinoSerialInterface()
+      : _isEnabled(false), _passthroughMode(false),
+        _controlSequenceReceived(false), _state(0), _controlSequencePos(0),
+        _frame_len(0), rx_len(0), _serial(nullptr),
+        _controlSequence(nullptr) {}
+
+  void begin(Stream& serial, const char* controlSequence = nullptr) {
+    _serial = &serial;
+    _controlSequence = controlSequence;
+    _passthroughMode = false;
+    _controlSequenceReceived = false;
+    resetReceiveState();
   #ifdef RAK_4631
     pinMode(WB_IO2, OUTPUT);
-  #endif  
+  #endif
   }
 
+  // In passthrough mode another line-oriented consumer owns the Stream. Binary
+  // frames are neither read from nor written to this interface.
+  void setPassthroughMode(bool enabled);
+  bool isPassthroughMode() const { return _passthroughMode; }
+
+  // Returns true once for each complete control sequence received while the
+  // binary frame parser was idle.
+  bool takeControlSequence();
+
   // BaseSerialInterface methods
   void enable() override;
   void disable() override;