[SX126x] Added frequency error reading

examples/SX126x/SX126x_Receive/SX126x_Receive.ino

@@ -88,6 +88,11 @@ void loop() {
     Serial.print(radio.getSNR());
     Serial.println(F(" dB"));
 
+    // print frequency error
+    Serial.print(F("[SX1262] Frequency error:\t"));
+    Serial.print(radio.getFrequencyError());
+    Serial.println(F(" Hz"));
+
   } else if (state == RADIOLIB_ERR_RX_TIMEOUT) {
     // timeout occurred while waiting for a packet
     Serial.println(F("timeout!"));

examples/SX126x/SX126x_Receive_Interrupt/SX126x_Receive_Interrupt.ino

@@ -127,6 +127,11 @@ void loop() {
       Serial.print(radio.getSNR());
       Serial.println(F(" dB"));
 
+      // print frequency error
+      Serial.print(F("[SX1262] Frequency error:\t"));
+      Serial.print(radio.getFrequencyError());
+      Serial.println(F(" Hz"));
+
     } else if (state == RADIOLIB_ERR_CRC_MISMATCH) {
       // packet was received, but is malformed
       Serial.println(F("CRC error!"));

src/modules/SX126x/SX126x.cpp

@@ -1241,6 +1241,39 @@ float SX126x::getSNR() {
   }
 }
 
+float SX126x::getFrequencyError() {
+  // check active modem
+  uint8_t modem = getPacketType();
+  if(modem != RADIOLIB_SX126X_PACKET_TYPE_LORA) {
+    return(0.0);
+  }
+
+  // read the raw frequency error register values
+  uint8_t efeRaw[3] = {0};
+  int16_t state = readRegister(RADIOLIB_SX126X_REG_FREQ_ERROR + 2, &efeRaw[0], 1);
+  RADIOLIB_ASSERT(state);
+  state = readRegister(RADIOLIB_SX126X_REG_FREQ_ERROR + 1, &efeRaw[1], 1);
+  RADIOLIB_ASSERT(state);
+  state = readRegister(RADIOLIB_SX126X_REG_FREQ_ERROR, &efeRaw[2], 1);
+  RADIOLIB_ASSERT(state);
+  uint32_t efe = ((uint32_t) efeRaw[0] << 16) | ((uint32_t) efeRaw[1] << 8) | efeRaw[2];
+  efe &= 0x0FFFFF;
+
+  float error = 0;
+
+  // check the first bit
+  if (efe & 0x80000) {
+    // frequency error is negative
+    efe |= (uint32_t) 0xFFF00000;
+    efe = ~efe + 1;
+    error = 1.55 * (float) efe / (160.0 / (float) _bwKhz) * -1.0;
+  } else {
+    error = 1.55 * (float) efe / (160.0 / (float) _bwKhz);
+  }
+
+  return(error);
+}
+
 size_t SX126x::getPacketLength(bool update) {
   (void)update;
   uint8_t rxBufStatus[2] = {0, 0};

src/modules/SX126x/SX126x.h

@@ -73,6 +73,9 @@
 #define RADIOLIB_SX126X_CMD_SET_SPECTR_SCAN_PARAMS             0x9B
 
 // SX126X register map
+#define RADIOLIB_SX126X_REG_RX_GAIN_RETENTION_0                0x029F // SX1268 datasheet v1.1, section 9.6
+#define RADIOLIB_SX126X_REG_RX_GAIN_RETENTION_1                0x02A0 // SX1268 datasheet v1.1, section 9.6
+#define RADIOLIB_SX126X_REG_RX_GAIN_RETENTION_2                0x02A1 // SX1268 datasheet v1.1, section 9.6
 #define RADIOLIB_SX126X_REG_VERSION_STRING                     0x0320
 #define RADIOLIB_SX126X_REG_HOPPING_ENABLE                     0x0385
 #define RADIOLIB_SX126X_REG_LR_FHSS_PACKET_LENGTH              0x0386
@@ -85,6 +88,7 @@
 #define RADIOLIB_SX126X_REG_LR_FHSS_FREQX_3(X)                 (0x038D + (X)*6)
 #define RADIOLIB_SX126X_REG_SPECTRAL_SCAN_RESULT               0x0401
 #define RADIOLIB_SX126X_REG_DIOX_OUT_ENABLE                    0x0580
+#define RADIOLIB_SX126X_REG_DIOX_DRIVE_STRENGTH                0x0582
 #define RADIOLIB_SX126X_REG_DIOX_IN_ENABLE                     0x0583
 #define RADIOLIB_SX126X_REG_DIOX_PULL_UP_CTRL                  0x0584
 #define RADIOLIB_SX126X_REG_DIOX_PULL_DOWN_CTRL                0x0585
@@ -120,7 +124,7 @@
 #define RADIOLIB_SX126X_REG_RANDOM_NUMBER_1                    0x081A
 #define RADIOLIB_SX126X_REG_RANDOM_NUMBER_2                    0x081B
 #define RADIOLIB_SX126X_REG_RANDOM_NUMBER_3                    0x081C
-#define RADIOLIB_SX126X_REG_TX_MODULATION                      0x0889
+#define RADIOLIB_SX126X_REG_SENSITIVITY_CONFIG                 0x0889 // SX1268 datasheet v1.1, section 15.1
 #define RADIOLIB_SX126X_REG_RF_FREQUENCY_0                     0x088B
 #define RADIOLIB_SX126X_REG_RF_FREQUENCY_1                     0x088C
 #define RADIOLIB_SX126X_REG_RF_FREQUENCY_2                     0x088D
@@ -138,13 +142,6 @@
 #define RADIOLIB_SX126X_REG_EVENT_MASK                         0x0944
 #define RADIOLIB_SX126X_REG_PATCH_MEMORY_BASE                  0x8000
 
-// undocumented registers
-#define RADIOLIB_SX126X_REG_SENSITIVITY_CONFIG                 0x0889 // SX1268 datasheet v1.1, section 15.1
-#define RADIOLIB_SX126X_REG_RX_GAIN_RETENTION_0                0x029F // SX1268 datasheet v1.1, section 9.6
-#define RADIOLIB_SX126X_REG_RX_GAIN_RETENTION_1                0x02A0 // SX1268 datasheet v1.1, section 9.6
-#define RADIOLIB_SX126X_REG_RX_GAIN_RETENTION_2                0x02A1 // SX1268 datasheet v1.1, section 9.6
-
-
 // SX126X SPI command variables
 //RADIOLIB_SX126X_CMD_SET_SLEEP                                                MSB   LSB   DESCRIPTION
 #define RADIOLIB_SX126X_SLEEP_START_COLD                       0b00000000  //  2     2     sleep mode: cold start, configuration is lost (default)
@@ -931,6 +928,15 @@ class SX126x: public PhysicalLayer {
     */
     float getSNR();
 
+    /*!
+      \brief Gets frequency error of the latest received packet.
+      WARNING: This functionality is based on SX128x implementation and not documented on SX126x.
+      While it seems to be working, it should be used with caution!
+
+      \returns Frequency error in Hz.
+    */
+    float getFrequencyError();
+
     /*!
       \brief Query modem for the packet length of received payload.