Initial commit: RNodeTHV4 boundary mode firmware for Heltec V4

Bridges LoRa mesh and TCP/WiFi backbone networks using microReticulum.
Based on microReticulum_Firmware with boundary mode additions:
- BoundaryMode.h: State management and EEPROM persistence
- BoundaryConfig.h: WiFi captive portal for configuration
- TcpInterface.h: TCP backbone interface with HDLC framing
- Display.h: Custom OLED layout with network status indicators
- Transport/Identity library patches for embedded memory constraints

sx126x.h

@@ -0,0 +1,150 @@
+// Copyright Sandeep Mistry, Mark Qvist and Jacob Eva.
+// Licensed under the MIT license.
+
+#ifndef SX126X_H
+#define SX126X_H
+
+#include <Arduino.h>
+#include <SPI.h>
+#include "Modem.h"
+
+#define LORA_DEFAULT_SS_PIN    10
+#define LORA_DEFAULT_RESET_PIN 9
+#define LORA_DEFAULT_DIO0_PIN  2
+#define LORA_DEFAULT_RXEN_PIN  -1
+#define LORA_DEFAULT_TXEN_PIN  -1
+#define LORA_DEFAULT_BUSY_PIN  -1
+#define LORA_MODEM_TIMEOUT_MS 20E3
+
+#define PA_OUTPUT_RFO_PIN      0
+#define PA_OUTPUT_PA_BOOST_PIN 1
+
+#define RSSI_OFFSET 157
+
+class sx126x : public Stream {
+public:
+  sx126x();
+
+  int begin(long frequency);
+  void end();
+
+  int beginPacket(int implicitHeader = false);
+  int endPacket();
+
+  int parsePacket(int size = 0);
+  int packetRssi();
+  int packetRssi(uint8_t pkt_snr_raw);
+  int currentRssi();
+  uint8_t packetRssiRaw();
+  uint8_t currentRssiRaw();
+  uint8_t packetSnrRaw();
+  float packetSnr();
+  long packetFrequencyError();
+
+  // from Print
+  virtual size_t write(uint8_t byte);
+  virtual size_t write(const uint8_t *buffer, size_t size);
+
+  // from Stream
+  virtual int available();
+  virtual int read();
+  virtual int peek();
+  virtual void flush();
+
+  void onReceive(void(*callback)(int));
+
+  void receive(int size = 0);
+  void standby();
+  void sleep();
+  void reset(void);
+
+  bool preInit();
+  uint8_t getTxPower();
+  void setTxPower(int level, int outputPin = PA_OUTPUT_PA_BOOST_PIN);
+  uint32_t getFrequency();
+  void setFrequency(long frequency);
+  void setSpreadingFactor(int sf);
+  long getSignalBandwidth();
+  void setSignalBandwidth(long sbw);
+  void setCodingRate4(int denominator);
+  void setPreambleLength(long preamble_symbols);
+  void setSyncWord(uint16_t sw);
+  bool dcd();
+  void enableCrc();
+  void disableCrc();
+  void enableTCXO();
+  void disableTCXO();
+
+  void rxAntEnable();
+  void loraMode();
+  void waitOnBusy();
+  void executeOpcode(uint8_t opcode, uint8_t *buffer, uint8_t size);
+  void executeOpcodeRead(uint8_t opcode, uint8_t *buffer, uint8_t size);
+  void writeBuffer(const uint8_t* buffer, size_t size);
+  void readBuffer(uint8_t* buffer, size_t size);
+  void setPacketParams(long preamble_symbols, uint8_t headermode, uint8_t payload_length, uint8_t crc);
+
+  void setModulationParams(uint8_t sf, uint8_t bw, uint8_t cr, int ldro);
+
+  // deprecated
+  void crc() { enableCrc(); }
+  void noCrc() { disableCrc(); }
+
+  byte random();
+
+  void setPins(int ss = LORA_DEFAULT_SS_PIN, int reset = LORA_DEFAULT_RESET_PIN, int dio0 = LORA_DEFAULT_DIO0_PIN, int busy = LORA_DEFAULT_BUSY_PIN, int rxen = LORA_DEFAULT_RXEN_PIN);
+  void setSPIFrequency(uint32_t frequency);
+
+  void dumpRegisters(Stream& out);
+
+private:
+  void explicitHeaderMode();
+  void implicitHeaderMode();
+
+  void handleDio0Rise();
+
+public:
+  // Poll for deferred DIO0 interrupt (call from main loop)
+  void pollDio0();
+
+private:  uint8_t readRegister(uint16_t address);
+  void writeRegister(uint16_t address, uint8_t value);
+  uint8_t singleTransfer(uint8_t opcode, uint16_t address, uint8_t value);
+
+  static void onDio0Rise();
+
+  void handleLowDataRate();
+  void optimizeModemSensitivity();
+
+  void calibrate(void);
+  void calibrate_image(long frequency);
+
+private:
+  SPISettings _spiSettings;
+  int _ss;
+  int _reset;
+  int _dio0;
+  int _rxen;
+  int _busy;
+  long _frequency;
+  int _txp;
+  uint8_t _sf;
+  uint8_t _bw;
+  uint8_t _cr;
+  uint8_t _ldro;
+  int _packetIndex;
+  int _preambleLength;
+  int _implicitHeaderMode;
+  int _payloadLength;
+  int _crcMode;
+  int _fifo_tx_addr_ptr;
+  int _fifo_rx_addr_ptr;
+  uint8_t _packet[255];
+  bool _preinit_done;
+  volatile bool _dio0_risen;
+  void (*_onReceive)(int);
+};
+
+extern sx126x sx126x_modem;
+
+#endif