[SX128x] Added support for changing LoRa sync word (#311)

src/modules/SX128x/SX128x.cpp

@@ -5,7 +5,7 @@ SX128x::SX128x(Module* mod) : PhysicalLayer(SX128X_FREQUENCY_STEP_SIZE, SX128X_M
   _mod = mod;
 }
 
-int16_t SX128x::begin(float freq, float bw, uint8_t sf, uint8_t cr, int8_t power, uint16_t preambleLength) {
+int16_t SX128x::begin(float freq, float bw, uint8_t sf, uint8_t cr, uint8_t syncWord, int8_t power, uint16_t preambleLength) {
   // set module properties
   _mod->init(RADIOLIB_USE_SPI);
   Module::pinMode(_mod->getIrq(), INPUT);
@@ -48,6 +48,9 @@ int16_t SX128x::begin(float freq, float bw, uint8_t sf, uint8_t cr, int8_t power
   state = setCodingRate(cr);
   RADIOLIB_ASSERT(state);
 
+  state = setSyncWord(syncWord);
+  RADIOLIB_ASSERT(state);
+
   state = setPreambleLength(preambleLength);
   RADIOLIB_ASSERT(state);
 
@@ -906,6 +909,17 @@ int16_t SX128x::setSyncWord(uint8_t* syncWord, uint8_t len) {
   return(setPacketParamsGFSK(_preambleLengthGFSK, _syncWordLen, _syncWordMatch, _crcGFSK, _whitening));
 }
 
+int16_t SX128x::setSyncWord(uint8_t syncWord, uint8_t controlBits) {
+  // check active modem
+  if(getPacketType() != SX128X_PACKET_TYPE_LORA) {
+    return(ERR_WRONG_MODEM);
+  }
+
+  // update register
+  uint8_t data[2] = {(uint8_t)((syncWord & 0xF0) | ((controlBits & 0xF0) >> 4)), (uint8_t)(((syncWord & 0x0F) << 4) | (controlBits & 0x0F))};
+  return(writeRegister(SX128X_REG_LORA_SYNC_WORD_MSB, data, 2));
+}
+
 int16_t SX128x::setCRC(uint8_t len, uint32_t initial, uint16_t polynomial) {
   // check active modem
   uint8_t modem = getPacketType();

src/modules/SX128x/SX128x.h

@@ -375,13 +375,15 @@ class SX128x: public PhysicalLayer {
 
       \param cr LoRa coding rate denominator. Defaults to 7 (coding rate 4/7).
 
+      \param syncWord 2-byte LoRa sync word. Defaults to SX128X_SYNC_WORD_PRIVATE (0x12).
+
       \param power Output power in dBm. Defaults to 10 dBm.
 
       \param preambleLength LoRa preamble length in symbols. Defaults to 12 symbols.
 
       \returns \ref status_codes
     */
-    int16_t begin(float freq = 2400.0, float bw = 812.5, uint8_t sf = 9, uint8_t cr = 7, int8_t power = 10, uint16_t preambleLength = 12);
+    int16_t begin(float freq = 2400.0, float bw = 812.5, uint8_t sf = 9, uint8_t cr = 7, uint8_t syncWord = SX128X_SYNC_WORD_PRIVATE, int8_t power = 10, uint16_t preambleLength = 12);
 
     /*!
       \brief Initialization method for GFSK modem.
@@ -666,6 +668,17 @@ class SX128x: public PhysicalLayer {
     */
     int16_t setSyncWord(uint8_t* syncWord, uint8_t len);
 
+    /*!
+      \brief Sets LoRa sync word.
+
+      \param syncWord LoRa sync word to be set.
+
+      \param controlBits Undocumented control bits, required for compatibility purposes.
+
+      \returns \ref status_codes
+    */
+    int16_t setSyncWord(uint8_t syncWord, uint8_t controlBits = 0x44);
+
     /*!
       \brief Sets CRC configuration.