Merge pull request #1954 from OverkillFPV/lora-longer-preamble

Lora longer preamble

src/helpers/radiolib/CustomLLCC68Wrapper.h

@@ -20,6 +20,7 @@ public:
     int sf = ((CustomLLCC68 *)_radio)->spreadingFactor;
     return packetScoreInt(snr, sf, packet_len);
   }
+  uint8_t getSpreadingFactor() const override { return ((CustomLLCC68 *)_radio)->spreadingFactor; }
 
   void doResetAGC() override { sx126xResetAGC((SX126x *)_radio); }
 

src/helpers/radiolib/CustomLR1110.h

@@ -36,4 +36,6 @@ class CustomLR1110 : public LR1110 {
       bool detected = ((irq & RADIOLIB_LR11X0_IRQ_SYNC_WORD_HEADER_VALID) || (irq & RADIOLIB_LR11X0_IRQ_PREAMBLE_DETECTED));
       return detected;
     }
+
+    uint8_t getSpreadingFactor() const { return spreadingFactor; }
 };

src/helpers/radiolib/CustomLR1110Wrapper.h

@@ -19,12 +19,14 @@ public:
 
   void onSendFinished() override {
     RadioLibWrapper::onSendFinished();
-    _radio->setPreambleLength(16); // overcomes weird issues with small and big pkts
+    _radio->setPreambleLength(preambleLengthForSF(getSpreadingFactor())); // overcomes weird issues with small and big pkts
   }
 
   float getLastRSSI() const override { return ((CustomLR1110 *)_radio)->getRSSI(); }
   float getLastSNR() const override { return ((CustomLR1110 *)_radio)->getSNR(); }
 
+  uint8_t getSpreadingFactor() const override { return ((CustomLR1110 *)_radio)->getSpreadingFactor(); }
+  
   void setRxBoostedGainMode(bool en) override {
     ((CustomLR1110 *)_radio)->setRxBoostedGainMode(en);
   }

src/helpers/radiolib/CustomSTM32WLxWrapper.h

@@ -21,6 +21,7 @@ public:
     int sf = ((CustomSTM32WLx *)_radio)->spreadingFactor;
     return packetScoreInt(snr, sf, packet_len);
   }
+  uint8_t getSpreadingFactor() const override { return ((CustomSTM32WLx *)_radio)->spreadingFactor; }
 
   void doResetAGC() override { sx126xResetAGC((SX126x *)_radio); }
 };

src/helpers/radiolib/CustomSX1262Wrapper.h

@@ -24,6 +24,7 @@ public:
     int sf = ((CustomSX1262 *)_radio)->spreadingFactor;
     return packetScoreInt(snr, sf, packet_len);
   }
+  uint8_t getSpreadingFactor() const override { return ((CustomSX1262 *)_radio)->spreadingFactor; }
   virtual void powerOff() override {
     ((CustomSX1262 *)_radio)->sleep(false);
   }

src/helpers/radiolib/CustomSX1268Wrapper.h

@@ -24,6 +24,7 @@ public:
     int sf = ((CustomSX1268 *)_radio)->spreadingFactor;
     return packetScoreInt(snr, sf, packet_len);
   }
+  uint8_t getSpreadingFactor() const override { return ((CustomSX1268 *)_radio)->spreadingFactor; }
 
   void doResetAGC() override { sx126xResetAGC((SX126x *)_radio); }
 

src/helpers/radiolib/CustomSX1276Wrapper.h

@@ -23,4 +23,5 @@ public:
     int sf = ((CustomSX1276 *)_radio)->spreadingFactor;
     return packetScoreInt(snr, sf, packet_len);
   }
+  uint8_t getSpreadingFactor() const override { return ((CustomSX1276 *)_radio)->spreadingFactor; }
 };

src/helpers/radiolib/RadioLibWrappers.cpp

@@ -26,6 +26,8 @@ void setFlag(void) {
 
 void RadioLibWrapper::begin() {
   _radio->setPacketReceivedAction(setFlag);  // this is also SentComplete interrupt
+  _preamble_sf = getSpreadingFactor();
+  _radio->setPreambleLength(preambleLengthForSF(_preamble_sf)); // longer preamble for lower SF improves reliability
   state = STATE_IDLE;
 
   if (_board->getStartupReason() == BD_STARTUP_RX_PACKET) {  // received a LoRa packet (while in deep sleep)

src/helpers/radiolib/RadioLibWrappers.h

@@ -11,6 +11,7 @@ protected:
   int16_t _noise_floor, _threshold;
   uint16_t _num_floor_samples;
   int32_t _floor_sample_sum;
+  uint8_t _preamble_sf;
 
   void idle();
   void startRecv();
@@ -19,7 +20,7 @@ protected:
   virtual void doResetAGC();
 
 public:
-  RadioLibWrapper(PhysicalLayer& radio, mesh::MainBoard& board) : _radio(&radio), _board(&board) { n_recv = n_sent = 0; }
+  RadioLibWrapper(PhysicalLayer& radio, mesh::MainBoard& board) : _radio(&radio), _board(&board), _preamble_sf(0) { n_recv = n_sent = 0; }
 
   void begin() override;
   virtual void powerOff() { _radio->sleep(); }
@@ -38,6 +39,9 @@ public:
   }
 
   virtual float getCurrentRSSI() =0;
+  virtual uint8_t getSpreadingFactor() const { return LORA_SF; }
+  static uint16_t preambleLengthForSF(uint8_t sf) { return sf <= 8 ? 32 : 16; }
+  void updatePreamble(uint8_t sf) { _preamble_sf = sf; _radio->setPreambleLength(preambleLengthForSF(sf)); }
 
   int getNoiseFloor() const override { return _noise_floor; }
   void triggerNoiseFloorCalibrate(int threshold) override;