Fix Cascade power saving, USB Companion, and mOTA flows

src/helpers/ArduinoSerialInterface.h

@@ -9,6 +9,14 @@ public:
   typedef bool (*ConnectedCheck)();
 
 private:
+  static constexpr uint8_t TX_QUEUE_SIZE = 4;
+  static constexpr uint32_t RX_FRAME_TIMEOUT_MS = 1000;
+
+  struct TxFrame {
+    uint16_t len;
+    uint8_t buf[MAX_FRAME_SIZE + 3];
+  };
+
   bool _isEnabled;
   bool _passthroughMode;
   bool _controlSequenceReceived;
@@ -20,15 +28,24 @@ private:
   uint16_t _frame_len;
   uint16_t rx_len;
   uint32_t _last_frame_ms;
+  uint32_t _last_rx_byte_ms;
+  bool _has_received_frame;
   Stream* _serial;
   const char* _controlSequence;
   const char* _secondaryControlSequence;
   ConnectedCheck _conn_check;
   uint8_t rx_buf[MAX_FRAME_SIZE];
+  TxFrame _tx_queue[TX_QUEUE_SIZE];
+  uint8_t _tx_queue_len;
+  uint16_t _tx_offset;
 
   bool checkControlSequence(uint8_t c, const char* sequence,
                             size_t& position, bool& received);
   void resetReceiveState();
+  void serviceReceiveTimeout();
+  void resetTransmitState();
+  bool enqueueFrame(const uint8_t src[], size_t len);
+  void serviceTransmit();
 
 public:
   ArduinoSerialInterface()
@@ -36,8 +53,10 @@ public:
         _controlSequenceReceived(false), _secondaryControlSequenceReceived(false),
         _flow_ctl(false), _state(0), _controlSequencePos(0),
         _secondaryControlSequencePos(0), _frame_len(0), rx_len(0),
-        _last_frame_ms(0), _serial(nullptr), _controlSequence(nullptr),
-        _secondaryControlSequence(nullptr), _conn_check(nullptr) {}
+        _last_frame_ms(0), _last_rx_byte_ms(0), _has_received_frame(false),
+        _serial(nullptr), _controlSequence(nullptr),
+        _secondaryControlSequence(nullptr), _conn_check(nullptr),
+        _tx_queue_len(0), _tx_offset(0) {}
 
   void begin(Stream& serial, const char* controlSequence = nullptr,
              const char* secondaryControlSequence = nullptr) {
@@ -48,7 +67,9 @@ public:
     _controlSequenceReceived = false;
     _secondaryControlSequenceReceived = false;
     _last_frame_ms = 0;
+    _has_received_frame = false;
     resetReceiveState();
+    resetTransmitState();
   #ifdef RAK_4631
     pinMode(WB_IO2, OUTPUT);
   #endif
@@ -71,12 +92,17 @@ public:
   // millis() of the last completely received frame, 0 if none since boot.
   // Useful as an activity-based connection check where no DTR state exists.
   uint32_t getLastFrameMillis() const { return _last_frame_ms; }
+  bool hasReceivedFrame() const { return _has_received_frame; }
 
-  // Optional: only hand a frame to the stream when it fits into the TX buffer
-  // as a whole, and report busy while it does not, so bulk streams get paced.
+  // Optional: queue complete frames and drain one at a time according to the
+  // stream's TX capacity, so short writes cannot discard or interleave bytes.
+  // Report busy while a frame remains queued so bulk streams get paced.
   // Only enable this for streams which really implement availableForWrite()
   // (USB-CDC does, the Print default returns 0).
-  void enableFlowControl(bool enable) { _flow_ctl = enable; }
+  void enableFlowControl(bool enable) {
+    if (!enable) resetTransmitState();
+    _flow_ctl = enable;
+  }
 
   // BaseSerialInterface methods
   void enable() override;
@@ -84,9 +110,11 @@ public:
   bool isEnabled() const override { return _isEnabled; }
 
   bool isConnected() const override;
+  void loop() override;
 
   bool isReadBusy() const override;
   bool isWriteBusy() const override;
+  bool hasPendingIO() const override;
   size_t writeFrame(const uint8_t src[], size_t len) override;
   size_t checkRecvFrame(uint8_t dest[]) override;
 };