[SX126x] Add workaround for GFSK

src/modules/SX126x/SX126x.cpp

@@ -1386,6 +1386,48 @@ int16_t SX126x::fixInvertedIQ(uint8_t iqConfig) {
   return(writeRegister(RADIOLIB_SX126X_REG_IQ_CONFIG, &iqConfigCurrent, 1));
 }
 
+int16_t SX126x::fixGFSK() {
+  // method that applies some magic workaround for specific bitrate, frequency deviation,
+  // receiver bandwidth and carrier frequencies for GFSK (and resets it in all other cases)
+  // this is not documented in the datasheet, only in Semtech repositories for SX126x and LR11xx
+
+  // first, check we are using GFSK modem
+  if(getPacketType() != RADIOLIB_SX126X_PACKET_TYPE_GFSK) {
+    // not in GFSK, nothing to do here
+    return(RADIOLIB_ERR_NONE);
+  }
+
+  // next, decide what to change based on modulation properties
+  int16_t state = RADIOLIB_ERR_UNKNOWN;
+  if(this->bitRate == 1200) {
+    // workaround for 1.2 kbps
+    state = this->mod->SPIsetRegValue(RADIOLIB_SX126X_REG_GFSK_FIX_3, 0x00, 4, 4);
+
+  } else if(this->bitRate == 600)  {
+    // workaround for 0.6 kbps
+    state = this->mod->SPIsetRegValue(RADIOLIB_SX126X_REG_GFSK_FIX_1, 0x18, 4, 3);
+    RADIOLIB_ASSERT(state);
+    state = this->mod->SPIsetRegValue(RADIOLIB_SX126X_REG_RSSI_AVG_WINDOW, 0x04, 4, 2);
+    RADIOLIB_ASSERT(state);
+    state = this->mod->SPIsetRegValue(RADIOLIB_SX126X_REG_GFSK_FIX_3, 0x00, 4, 4);
+    RADIOLIB_ASSERT(state);
+    state = this->mod->SPIsetRegValue(RADIOLIB_SX126X_REG_GFSK_FIX_4, 0x50, 6, 4);
+  
+  } else {
+    // reset
+    state = this->mod->SPIsetRegValue(RADIOLIB_SX126X_REG_GFSK_FIX_1, 0x08, 4, 3);
+    RADIOLIB_ASSERT(state);
+    state = this->mod->SPIsetRegValue(RADIOLIB_SX126X_REG_RSSI_AVG_WINDOW, 0x00, 4, 2);
+    RADIOLIB_ASSERT(state);
+    state = this->mod->SPIsetRegValue(RADIOLIB_SX126X_REG_GFSK_FIX_3, 0x10, 4, 4);
+    RADIOLIB_ASSERT(state);
+    state = this->mod->SPIsetRegValue(RADIOLIB_SX126X_REG_GFSK_FIX_4, 0x00, 6, 4);
+  
+  }
+
+  return(state);
+}
+
 Module* SX126x::getMod() {
   return(this->mod);
 }

src/modules/SX126x/SX126x.h

@@ -905,6 +905,7 @@ class SX126x: public PhysicalLayer {
     int16_t fixSensitivity();
     int16_t fixImplicitTimeout();
     int16_t fixInvertedIQ(uint8_t iqConfig);
+    int16_t fixGFSK();
 
     // LR-FHSS utilities
     int16_t buildLRFHSSPacket(const uint8_t* in, size_t in_len, uint8_t* out, size_t* out_len, size_t* out_bits, size_t* out_hops);

src/modules/SX126x/SX126x_config.cpp

@@ -238,10 +238,16 @@ int16_t SX126x::setBitRate(float br) {
   this->bitRate = brRaw;
 
   // update modulation parameters
+  int16_t state = RADIOLIB_ERR_UNKNOWN;
   if(modem == RADIOLIB_SX126X_PACKET_TYPE_BPSK) {
-    return(setModulationParamsBPSK(this->bitRate));
+    state = setModulationParamsBPSK(this->bitRate);
+  } else {
+    state = setModulationParamsFSK(this->bitRate, this->pulseShape, this->rxBandwidth, this->frequencyDev);
   }
-  return(setModulationParamsFSK(this->bitRate, this->pulseShape, this->rxBandwidth, this->frequencyDev));
+  RADIOLIB_ASSERT(state);
+
+  // apply workaround or reset it, as needed
+  return(fixGFSK());
 }
 
 int16_t SX126x::setDataRate(DataRate_t dr, ModemType_t modem) {

src/modules/SX126x/SX126x_registers.h

@@ -29,6 +29,7 @@
 #define RADIOLIB_SX126X_REG_TX_BITBANG_ENABLE_0                 0x0587
 #define RADIOLIB_SX126X_REG_PATCH_UPDATE_ENABLE                 0x0610
 #define RADIOLIB_SX126X_REG_TX_BITBANG_ENABLE_1                 0x0680
+#define RADIOLIB_SX126X_REG_GFSK_FIX_4                          0x06AC
 #define RADIOLIB_SX126X_REG_WHITENING_INITIAL_MSB               0x06B8
 #define RADIOLIB_SX126X_REG_WHITENING_INITIAL_LSB               0x06B9
 #define RADIOLIB_SX126X_REG_RX_TX_PLD_LEN                       0x06BB
@@ -46,6 +47,7 @@
 #define RADIOLIB_SX126X_REG_SYNC_WORD_7                         0x06C7
 #define RADIOLIB_SX126X_REG_NODE_ADDRESS                        0x06CD
 #define RADIOLIB_SX126X_REG_BROADCAST_ADDRESS                   0x06CE
+#define RADIOLIB_SX126X_REG_GFSK_FIX_1                          0x06D1
 #define RADIOLIB_SX126X_REG_PAYLOAD_LENGTH                      0x0702
 #define RADIOLIB_SX126X_REG_PACKET_PARAMS                       0x0704
 #define RADIOLIB_SX126X_REG_LORA_SYNC_TIMEOUT                   0x0706
@@ -67,6 +69,7 @@
 #define RADIOLIB_SX126X_REG_RF_FREQUENCY_3                      0x088E
 #define RADIOLIB_SX126X_REG_RSSI_AVG_WINDOW                     0x089B
 #define RADIOLIB_SX126X_REG_RX_GAIN                             0x08AC
+#define RADIOLIB_SX126X_REG_GFSK_FIX_3                          0x08B8
 #define RADIOLIB_SX126X_REG_TX_CLAMP_CONFIG                     0x08D8
 #define RADIOLIB_SX126X_REG_ANA_LNA                             0x08E2
 #define RADIOLIB_SX126X_REG_LNA_CAP_TUNE_N                      0x08E3