workaround for LR1110 shift issue

it seems that if the LR1110 radio hears a packet corrupted in a specific way, it'll report a packet of 0 length and with the header error IRQ set. every packet received afterwards will then be shifted to the right by 4 bytes on top of the radio's reported offset. this can occur multiple times with the shift increasing by 4 bytes each time. thus, this patch will read from an additional offset after hearing the trigger packet.
transmitting seems to reset the shift - unsure exactly what operation resets it but standby() is called after tx so patch assumes shift is 0 after standby(). more investigation may be needed here.

Author: Woodie-07

platformio.ini

@@ -18,7 +18,7 @@ monitor_speed = 115200
 lib_deps =
   SPI
   Wire
-  jgromes/RadioLib @ ^7.1.2
+  jgromes/RadioLib @ ^7.3.0
   rweather/Crypto @ ^0.4.0
   adafruit/RTClib @ ^2.1.3
   melopero/Melopero RV3028 @ ^1.1.0

src/helpers/radiolib/CustomLR1110.h

@@ -9,6 +9,74 @@ class CustomLR1110 : public LR1110 {
   public:
     CustomLR1110(Module *mod) : LR1110(mod) { }
 
+    uint8_t shiftCount = 0;
+
+    int16_t standby() override {
+      // tx resets the shift, standby is called on tx completion
+      // this might not actually be what resets it, but it seems to work
+      // more investigation needed
+      this->shiftCount = 0;
+      return LR1110::standby();
+    }
+
+    size_t getPacketLength(bool update) override {
+      size_t len = LR1110::getPacketLength(update);
+      if (len == 0) {
+        uint32_t irq = getIrqStatus();
+        if (irq & RADIOLIB_LR11X0_IRQ_HEADER_ERR) {
+          Serial.println(F("got possible bug packet"));
+          this->shiftCount += 4; // uint8 will loop around to 0 at 256, perfect as rx buffer is 256 bytes
+        } else {
+          Serial.println(F("got zero-length packet without header err irq"));
+        }
+      }
+      return len;
+    }
+
+    int16_t readData(uint8_t *data, size_t len) override {
+      // check active modem
+      uint8_t modem = RADIOLIB_LR11X0_PACKET_TYPE_NONE;
+      int16_t state = getPacketType(&modem);
+      RADIOLIB_ASSERT(state);
+      if((modem != RADIOLIB_LR11X0_PACKET_TYPE_LORA) && 
+        (modem != RADIOLIB_LR11X0_PACKET_TYPE_GFSK)) {
+        return(RADIOLIB_ERR_WRONG_MODEM);
+      }
+
+      // check integrity CRC
+      uint32_t irq = getIrqStatus();
+      int16_t crcState = RADIOLIB_ERR_NONE;
+      // Report CRC mismatch when there's a payload CRC error, or a header error and no valid header (to avoid false alarm from previous packet)
+      if((irq & RADIOLIB_LR11X0_IRQ_CRC_ERR) || ((irq & RADIOLIB_LR11X0_IRQ_HEADER_ERR) && !(irq & RADIOLIB_LR11X0_IRQ_SYNC_WORD_HEADER_VALID))) {
+        crcState = RADIOLIB_ERR_CRC_MISMATCH;
+      }
+
+      // get packet length
+      // the offset is needed since LR11x0 seems to move the buffer base by 4 bytes on every packet
+      uint8_t offset = 0;
+      size_t length = LR1110::getPacketLength(true, &offset);
+      if((len != 0) && (len < length)) {
+        // user requested less data than we got, only return what was requested
+        length = len;
+      }
+
+      // read packet data
+      state = readBuffer8(data, length, (uint8_t)(offset + this->shiftCount));  // add shiftCount to offset - only change from radiolib
+      RADIOLIB_ASSERT(state);
+
+      // clear the Rx buffer
+      state = clearRxBuffer();
+      RADIOLIB_ASSERT(state);
+
+      // clear interrupt flags
+      state = clearIrqState(RADIOLIB_LR11X0_IRQ_ALL);
+
+      // check if CRC failed - this is done after reading data to give user the option to keep them
+      RADIOLIB_ASSERT(crcState);
+
+      return(state);
+    }
+
     RadioLibTime_t getTimeOnAir(size_t len) override {
   // calculate number of symbols
   float N_symbol = 0;