Improve support for LoRa coding rate with Long Interleaver (#1606)

* Add error for packet too short

* [SX126x] Add support for Long Interleaver coding rates

* [LR11x0] Add packet length check for long interleaver

* [LR11x0] Update comment on Long Interleaver

* [SX128x] Update Long Interleaver CR 4/8 macro

* [SX128x] Add packet length check for CR 4/8 with long interleaver

* [SX126x] Add definitions for new CR with long interleaver

src/TypeDef.h

@@ -255,6 +255,11 @@
 */
 #define RADIOLIB_ERR_INVALID_IRQ                               (-29)
 
+/*!
+  \brief Packet supplied to transmission method was shorter than required.
+*/
+#define RADIOLIB_ERR_PACKET_TOO_SHORT                          (-30)
+
 // RF69-specific status codes
 
 /*!

src/modules/LR11x0/LR11x0.cpp

@@ -179,6 +179,17 @@ int16_t LR11x0::transmit(const uint8_t* data, size_t len, uint8_t addr) {
   RADIOLIB_ASSERT(state);
 
   // check packet length
+  if (this->codingRate > RADIOLIB_LR11X0_LORA_CR_4_8_SHORT) {
+    // Long Interleaver needs at least 8 bytes
+    if(len < 8) {
+      return(RADIOLIB_ERR_PACKET_TOO_SHORT);
+    }
+
+    // Long Interleaver supports up to 253 bytes if CRC is enabled
+    if (this->crcTypeLoRa == RADIOLIB_LR11X0_LORA_CRC_ENABLED && (len > RADIOLIB_LR11X0_MAX_PACKET_LENGTH - 2)) {
+      return(RADIOLIB_ERR_PACKET_TOO_LONG);
+    }  
+  } 
   if(len > RADIOLIB_LR11X0_MAX_PACKET_LENGTH) {
     return(RADIOLIB_ERR_PACKET_TOO_LONG);
   }

src/modules/LR11x0/LR11x0.h

@@ -1172,7 +1172,8 @@ class LR11x0: public PhysicalLayer {
       is undocumented and not recommended without your own FEC.
       \param cr LoRa coding rate denominator to be set.
       \param longInterleave Enable long interleaver when set to true.
-      Note that CR 4/7 is not possible with long interleaver enabled!
+      Note that with long interleaver enabled, CR 4/7 is not possible, there are packet length restrictions,
+      and it is not compatible with SX127x radios!
       \returns \ref status_codes
     */
     int16_t setCodingRate(uint8_t cr, bool longInterleave = false);

src/modules/SX126x/SX126x.cpp

@@ -200,6 +200,17 @@ int16_t SX126x::transmit(const uint8_t* data, size_t len, uint8_t addr) {
   RADIOLIB_ASSERT(state);
 
   // check packet length
+  if(this->codingRate > RADIOLIB_SX126X_LORA_CR_4_8) {
+    // Long Interleaver needs at least 8 bytes
+    if(len < 8) {
+      return(RADIOLIB_ERR_PACKET_TOO_SHORT);
+    }
+
+    // Long Interleaver supports up to 253 bytes if CRC is enabled
+    if(this->crcTypeLoRa == RADIOLIB_SX126X_LORA_CRC_ON && (len > RADIOLIB_SX126X_MAX_PACKET_LENGTH - 2)) {
+      return(RADIOLIB_ERR_PACKET_TOO_LONG);
+    }  
+  } 
   if(len > RADIOLIB_SX126X_MAX_PACKET_LENGTH) {
     return(RADIOLIB_ERR_PACKET_TOO_LONG);
   }
@@ -847,9 +858,17 @@ RadioLibTime_t SX126x::getTimeOnAir(size_t len) {
   PacketConfig_t packetConfig = {};
 
   if(type == RADIOLIB_SX126X_PACKET_TYPE_LORA) {
+    uint8_t cr = this->codingRate;
+    // We assume same calculation for short and long interleaving, so map CR values 0-4 and 5-7 to the same values
+    if (cr < 5) {
+      cr = cr + 4;
+    } else if (cr == 7) {
+      cr = cr + 1;
+    }
+
+    dataRate.lora.codingRate = cr;
     dataRate.lora.spreadingFactor = this->spreadingFactor;
     dataRate.lora.bandwidth = this->bandwidthKhz;
-    dataRate.lora.codingRate = (uint8_t)(this->codingRate + 4);
 
     packetConfig.lora.preambleLength = this->preambleLengthLoRa;
     packetConfig.lora.crcEnabled = (bool)this->crcTypeLoRa;

src/modules/SX126x/SX126x.h

@@ -352,9 +352,12 @@ class SX126x: public PhysicalLayer {
       \brief Sets LoRa coding rate denominator. Allowed values range from 4 to 8. Note that a value of 4 means no coding, 
       is undocumented and not recommended without your own FEC.
       \param cr LoRa coding rate denominator to be set.
+      \param longInterleave Enable long interleaver when set to true.
+      Note that with long interleaver enabled, CR 4/7 is not possible, there are packet length restrictions,
+      and it is not compatible with SX127x radios.
       \returns \ref status_codes
     */
-    int16_t setCodingRate(uint8_t cr);
+    int16_t setCodingRate(uint8_t cr, bool longInterleave = false);
 
     /*!
       \brief Sets LoRa sync word.

src/modules/SX126x/SX126x_config.cpp

@@ -105,7 +105,7 @@ int16_t SX126x::setSpreadingFactor(uint8_t sf) {
   return(setModulationParams(this->spreadingFactor, this->bandwidth, this->codingRate, this->ldrOptimize));
 }
 
-int16_t SX126x::setCodingRate(uint8_t cr) {
+int16_t SX126x::setCodingRate(uint8_t cr, bool longInterleave) {
   // check active modem
   if(getPacketType() != RADIOLIB_SX126X_PACKET_TYPE_LORA) {
     return(RADIOLIB_ERR_WRONG_MODEM);
@@ -113,8 +113,26 @@ int16_t SX126x::setCodingRate(uint8_t cr) {
 
   RADIOLIB_CHECK_RANGE(cr, 4, 8, RADIOLIB_ERR_INVALID_CODING_RATE);
 
+  if(longInterleave) {
+    switch(cr) {
+      case 4:
+        this->codingRate = 0;
+        break;
+      case 5:
+      case 6:
+        this->codingRate = cr;
+        break;
+      case 8: 
+        this->codingRate = cr - 1;
+        break;
+      default:
+        return(RADIOLIB_ERR_INVALID_CODING_RATE);
+    }
+  } else {
+    this->codingRate = cr - 4;
+  }
+
   // update modulation parameters
-  this->codingRate = cr - 4;
   return(setModulationParams(this->spreadingFactor, this->bandwidth, this->codingRate, this->ldrOptimize));
 }
 

src/modules/SX126x/SX126x_registers.h

@@ -230,6 +230,9 @@
 #define RADIOLIB_SX126X_LORA_CR_4_6                             0x02        //  7     0                     4/6
 #define RADIOLIB_SX126X_LORA_CR_4_7                             0x03        //  7     0                     4/7
 #define RADIOLIB_SX126X_LORA_CR_4_8                             0x04        //  7     0                     4/8
+#define RADIOLIB_SX126X_LORA_CR_4_5_LI                          0x05        //  7     0                     4/5, long interleaver
+#define RADIOLIB_SX126X_LORA_CR_4_6_LI                          0x06        //  7     0                     4/6, long interleaver
+#define RADIOLIB_SX126X_LORA_CR_4_8_LI                          0x07        //  7     0                     4/8, long interleaver
 #define RADIOLIB_SX126X_LORA_LOW_DATA_RATE_OPTIMIZE_OFF         0x00        //  7     0   LoRa low data rate optimization: disabled
 #define RADIOLIB_SX126X_LORA_LOW_DATA_RATE_OPTIMIZE_ON          0x01        //  7     0                                    enabled
 

src/modules/SX128x/SX128x.cpp

@@ -315,7 +315,12 @@ int16_t SX128x::reset(bool verify) {
 
 int16_t SX128x::transmit(const uint8_t* data, size_t len, uint8_t addr) {
   // check packet length
-  if(len > RADIOLIB_SX128X_MAX_PACKET_LENGTH) {
+  if(this->codingRateLoRa == RADIOLIB_SX128X_LORA_CR_4_8_LI && this->crcLoRa == RADIOLIB_SX128X_LORA_CRC_ON) {
+    // Long Interleaver at CR 4/8 supports up to 253 bytes if CRC is enabled
+    if(len > RADIOLIB_SX128X_MAX_PACKET_LENGTH - 2) {
+      return(RADIOLIB_ERR_PACKET_TOO_LONG);
+    }
+  } else if(len > RADIOLIB_SX128X_MAX_PACKET_LENGTH) {
     return(RADIOLIB_ERR_PACKET_TOO_LONG);
   }
 

src/modules/SX128x/SX128x.h

@@ -253,7 +253,7 @@
 #define RADIOLIB_SX128X_LORA_CR_4_8                             0x04        //  7     0                     4/8
 #define RADIOLIB_SX128X_LORA_CR_4_5_LI                          0x05        //  7     0                     4/5, long interleaving
 #define RADIOLIB_SX128X_LORA_CR_4_6_LI                          0x06        //  7     0                     4/6, long interleaving
-#define RADIOLIB_SX128X_LORA_CR_4_7_LI                          0x07        //  7     0                     4/7, long interleaving
+#define RADIOLIB_SX128X_LORA_CR_4_8_LI                          0x07        //  7     0                     4/8, long interleaving
 
 //RADIOLIB_SX128X_CMD_SET_PACKET_PARAMS
 #define RADIOLIB_SX128X_GFSK_FLRC_SYNC_WORD_OFF                 0x00        //  7     0   GFSK/FLRC sync word used: none