[SX127x] Use length from startReceive in implicit header mode (#1345)

src/modules/SX127x/SX1272.cpp

@@ -497,11 +497,13 @@ int16_t SX1272::autoLDRO() {
 }
 
 int16_t SX1272::implicitHeader(size_t len) {
-  return(setHeaderType(RADIOLIB_SX1272_HEADER_IMPL_MODE, len));
+  this->implicitHdr = true;
+  return(setHeaderType(RADIOLIB_SX1272_HEADER_IMPL_MODE, 2, len));
 }
 
 int16_t SX1272::explicitHeader() {
-  return(setHeaderType(RADIOLIB_SX1272_HEADER_EXPL_MODE));
+  this->implicitHdr = false;
+  return(setHeaderType(RADIOLIB_SX1272_HEADER_EXPL_MODE, 2));
 }
 
 int16_t SX1272::setBandwidthRaw(uint8_t newBandwidth) {
@@ -521,11 +523,13 @@ int16_t SX1272::setSpreadingFactorRaw(uint8_t newSpreadingFactor) {
   // write registers
   Module* mod = this->getMod();
   if(newSpreadingFactor == RADIOLIB_SX127X_SF_6) {
+    this->implicitHdr = true;
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_MODEM_CONFIG_1, RADIOLIB_SX1272_HEADER_IMPL_MODE | (SX127x::crcEnabled ? RADIOLIB_SX1272_RX_CRC_MODE_ON : RADIOLIB_SX1272_RX_CRC_MODE_OFF), 2, 1);
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_MODEM_CONFIG_2, RADIOLIB_SX127X_SF_6 | RADIOLIB_SX127X_TX_MODE_SINGLE, 7, 3);
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_DETECT_OPTIMIZE, RADIOLIB_SX127X_DETECT_OPTIMIZE_SF_6, 2, 0);
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_DETECTION_THRESHOLD, RADIOLIB_SX127X_DETECTION_THRESHOLD_SF_6);
   } else {
+    this->implicitHdr = false;
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_MODEM_CONFIG_1, RADIOLIB_SX1272_HEADER_EXPL_MODE | (SX127x::crcEnabled ? RADIOLIB_SX1272_RX_CRC_MODE_ON : RADIOLIB_SX1272_RX_CRC_MODE_OFF),  2, 1);
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_MODEM_CONFIG_2, newSpreadingFactor | RADIOLIB_SX127X_TX_MODE_SINGLE, 7, 3);
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_DETECT_OPTIMIZE, RADIOLIB_SX127X_DETECT_OPTIMIZE_SF_7_12, 2, 0);
@@ -544,27 +548,6 @@ int16_t SX1272::setCodingRateRaw(uint8_t newCodingRate) {
   return(state);
 }
 
-int16_t SX1272::setHeaderType(uint8_t headerType, size_t len) {
-  // check active modem
-  if(getActiveModem() != RADIOLIB_SX127X_LORA) {
-    return(RADIOLIB_ERR_WRONG_MODEM);
-  }
-
-  // set requested packet mode
-  Module* mod = this->getMod();
-  int16_t state = mod->SPIsetRegValue(RADIOLIB_SX127X_REG_MODEM_CONFIG_1, headerType, 2, 2);
-  RADIOLIB_ASSERT(state);
-
-  // set length to register
-  state = mod->SPIsetRegValue(RADIOLIB_SX127X_REG_PAYLOAD_LENGTH, len);
-  RADIOLIB_ASSERT(state);
-
-  // update cached value
-  SX127x::packetLength = len;
-
-  return(state);
-}
-
 int16_t SX1272::configFSK() {
   // configure common registers
   int16_t state = SX127x::configFSK();

src/modules/SX127x/SX1272.h

@@ -316,7 +316,6 @@ class SX1272: public SX127x {
     int16_t setBandwidthRaw(uint8_t newBandwidth);
     int16_t setSpreadingFactorRaw(uint8_t newSpreadingFactor);
     int16_t setCodingRateRaw(uint8_t newCodingRate);
-    int16_t setHeaderType(uint8_t headerType, size_t len = 0xFF);
 
     int16_t configFSK();
     void errataFix(bool rx) override;

src/modules/SX127x/SX1278.cpp

@@ -535,11 +535,13 @@ int16_t SX1278::autoLDRO() {
 }
 
 int16_t SX1278::implicitHeader(size_t len) {
-  return(setHeaderType(RADIOLIB_SX1278_HEADER_IMPL_MODE, len));
+  this->implicitHdr = true;
+  return(setHeaderType(RADIOLIB_SX1278_HEADER_IMPL_MODE, 0, len));
 }
 
 int16_t SX1278::explicitHeader() {
-  return(setHeaderType(RADIOLIB_SX1278_HEADER_EXPL_MODE));
+  this->implicitHdr = false;
+  return(setHeaderType(RADIOLIB_SX1278_HEADER_EXPL_MODE, 0));
 }
 
 int16_t SX1278::setBandwidthRaw(uint8_t newBandwidth) {
@@ -559,11 +561,13 @@ int16_t SX1278::setSpreadingFactorRaw(uint8_t newSpreadingFactor) {
   // write registers
   Module* mod = this->getMod();
   if(newSpreadingFactor == RADIOLIB_SX127X_SF_6) {
+    this->implicitHdr = true;
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_MODEM_CONFIG_1, RADIOLIB_SX1278_HEADER_IMPL_MODE, 0, 0);
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_MODEM_CONFIG_2, RADIOLIB_SX127X_SF_6 | RADIOLIB_SX127X_TX_MODE_SINGLE, 7, 3);
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_DETECT_OPTIMIZE, RADIOLIB_SX127X_DETECT_OPTIMIZE_SF_6, 2, 0);
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_DETECTION_THRESHOLD, RADIOLIB_SX127X_DETECTION_THRESHOLD_SF_6);
   } else {
+    this->implicitHdr = false;
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_MODEM_CONFIG_1, RADIOLIB_SX1278_HEADER_EXPL_MODE, 0, 0);
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_MODEM_CONFIG_2, newSpreadingFactor | RADIOLIB_SX127X_TX_MODE_SINGLE, 7, 3);
     state |= mod->SPIsetRegValue(RADIOLIB_SX127X_REG_DETECT_OPTIMIZE, RADIOLIB_SX127X_DETECT_OPTIMIZE_SF_7_12, 2, 0);
@@ -582,27 +586,6 @@ int16_t SX1278::setCodingRateRaw(uint8_t newCodingRate) {
   return(state);
 }
 
-int16_t SX1278::setHeaderType(uint8_t headerType, size_t len) {
-  // check active modem
-  if(getActiveModem() != RADIOLIB_SX127X_LORA) {
-    return(RADIOLIB_ERR_WRONG_MODEM);
-  }
-
-  // set requested packet mode
-  Module* mod = this->getMod();
-  int16_t state = mod->SPIsetRegValue(RADIOLIB_SX127X_REG_MODEM_CONFIG_1, headerType, 0, 0);
-  RADIOLIB_ASSERT(state);
-
-  // set length to register
-  state = mod->SPIsetRegValue(RADIOLIB_SX127X_REG_PAYLOAD_LENGTH, len);
-  RADIOLIB_ASSERT(state);
-
-  // update cached value
-  SX127x::packetLength = len;
-
-  return(state);
-}
-
 int16_t SX1278::configFSK() {
   // configure common registers
   int16_t state = SX127x::configFSK();

src/modules/SX127x/SX1278.h

@@ -328,7 +328,6 @@ class SX1278: public SX127x {
     int16_t setBandwidthRaw(uint8_t newBandwidth);
     int16_t setSpreadingFactorRaw(uint8_t newSpreadingFactor);
     int16_t setCodingRateRaw(uint8_t newCodingRate);
-    int16_t setHeaderType(uint8_t headerType, size_t len = 0xFF);
 
     int16_t configFSK();
     void errataFix(bool rx) override;

src/modules/SX127x/SX127x.cpp

@@ -417,8 +417,9 @@ int16_t SX127x::startReceive(uint32_t timeout, RadioLibIrqFlags_t irqFlags, Radi
       state = this->mod->SPIsetRegValue(RADIOLIB_SX127X_REG_DIO_MAPPING_1, RADIOLIB_SX127X_DIO1_LORA_FHSS_CHANGE_CHANNEL, 5, 4);
     }
 
-    // set expected packet length for SF6
-    if(this->spreadingFactor == 6) {
+    // in implicit header mode, use the provided length if it is nonzero
+    // otherwise we trust the user has previously set the payload length manually
+    if((this->implicitHdr) && (len != 0)) {
       state |= this->mod->SPIsetRegValue(RADIOLIB_SX127X_REG_PAYLOAD_LENGTH, len);
       this->packetLength = len;
     }
@@ -1211,12 +1212,12 @@ size_t SX127x::getPacketLength(bool update) {
   int16_t modem = getActiveModem();
 
   if(modem == RADIOLIB_SX127X_LORA) {
-    if(this->spreadingFactor != 6) {
-      // get packet length for SF7 - SF12
+    if(!this->implicitHdr) {
+      // get packet length for explicit header mode
       return(this->mod->SPIreadRegister(RADIOLIB_SX127X_REG_RX_NB_BYTES));
 
     } else {
-      // return the cached value for SF6
+      // return the cached value for implicit header mode
       return(this->packetLength);
     }
 
@@ -1860,6 +1861,27 @@ float SX127x::getRSSI(bool packet, bool skipReceive, int16_t offset) {
   }
 }
 
+int16_t SX127x::setHeaderType(uint8_t headerType, uint8_t bitIndex, size_t len) {
+  // check active modem
+  if(getActiveModem() != RADIOLIB_SX127X_LORA) {
+    return(RADIOLIB_ERR_WRONG_MODEM);
+  }
+
+  // set requested packet mode
+  Module* mod = this->getMod();
+  int16_t state = mod->SPIsetRegValue(RADIOLIB_SX127X_REG_MODEM_CONFIG_1, headerType, bitIndex, bitIndex);
+  RADIOLIB_ASSERT(state);
+
+  // set length to register
+  state = mod->SPIsetRegValue(RADIOLIB_SX127X_REG_PAYLOAD_LENGTH, len);
+  RADIOLIB_ASSERT(state);
+
+  // update cached value
+  SX127x::packetLength = len;
+
+  return(state);
+}
+
 int16_t SX127x::setLowBatteryThreshold(int8_t level, uint32_t pin) {
   // check disable
   if(level < 0) {

src/modules/SX127x/SX127x.h

@@ -1249,12 +1249,14 @@ class SX127x: public PhysicalLayer {
     uint8_t codingRate = 0;
     bool crcEnabled = false;
     bool ookEnabled = false;
+    bool implicitHdr = false;
 
     int16_t configFSK();
     int16_t getActiveModem();
     int16_t setFrequencyRaw(float newFreq);
     int16_t setBitRateCommon(float br, uint8_t fracRegAddr);
     float getRSSI(bool packet, bool skipReceive, int16_t offset);
+    int16_t setHeaderType(uint8_t headerType, uint8_t bitIndex, size_t len = 0xFF);
 
 #if !RADIOLIB_GODMODE
   private: