[SX127x] Added check for LoRa header CRC mismatch (#200)

src/TypeDef.h

@@ -283,6 +283,11 @@
 */
 #define ERR_INVALID_ENCODING                          -23
 
+/*!
+  \brief LoRa packet header has been damaged.
+*/
+#define ERR_LORA_HEADER_DAMAGED                        -24
+
 // RF69-specific status codes
 
 /*!

src/modules/SX127x/SX1272.cpp

@@ -361,6 +361,7 @@ float SX1272::getRSSI() {
 int16_t SX1272::setCRC(bool enableCRC) {
   if(getActiveModem() == SX127X_LORA) {
     // set LoRa CRC
+    SX127x::_crcEnabled = enableCRC;
     if(enableCRC) {
       return(_mod->SPIsetRegValue(SX127X_REG_MODEM_CONFIG_2, SX1272_RX_CRC_MODE_ON, 2, 2));
     } else {

src/modules/SX127x/SX1278.cpp

@@ -439,6 +439,7 @@ float SX1278::getRSSI() {
 int16_t SX1278::setCRC(bool enableCRC) {
   if(getActiveModem() == SX127X_LORA) {
     // set LoRa CRC
+    SX127x::_crcEnabled = enableCRC;
     if(enableCRC) {
       return(_mod->SPIsetRegValue(SX127X_REG_MODEM_CONFIG_2, SX1278_RX_CRC_MODE_ON, 2, 2));
     } else {

src/modules/SX127x/SX127x.cpp

@@ -490,11 +490,18 @@ int16_t SX127x::readData(uint8_t* data, size_t len) {
       length = getPacketLength();
     }
 
-    // check integrity CRC
+    // check packet header integrity
+    if(_crcEnabled && (_mod->SPIgetRegValue(SX127X_REG_HOP_CHANNEL, 6, 6)) == 0) {
+      // CRC is disabled according to packet header and enabled according to user
+      // most likely damaged packet header
+      clearIRQFlags();
+      return(ERR_LORA_HEADER_DAMAGED);
+    }
+
+    // check payload CRC
     if(_mod->SPIgetRegValue(SX127X_REG_IRQ_FLAGS, 5, 5) == SX127X_CLEAR_IRQ_FLAG_PAYLOAD_CRC_ERROR) {
       // clear interrupt flags
       clearIRQFlags();
-
       return(ERR_CRC_MISMATCH);
     }
 

src/modules/SX127x/SX127x.h

@@ -950,6 +950,7 @@ class SX127x: public PhysicalLayer {
     float _br = 0;
     float _rxBw = 0;
     bool _ook = false;
+    bool _crcEnabled = false;
 
     int16_t setFrequencyRaw(float newFreq);
     int16_t config();