From c127712c5e4c90ad17ffe721ccbe025fb2d0cb21 Mon Sep 17 00:00:00 2001
From: jgromes <jgromes@users.noreply.github.com>
Date: Thu, 19 Nov 2020 17:07:32 +0100
Subject: [PATCH] [SX127x] Added check for LoRa header CRC mismatch (#200)

---
 src/TypeDef.h                 |  5 +++++
 src/modules/SX127x/SX1272.cpp |  1 +
 src/modules/SX127x/SX1278.cpp |  1 +
 src/modules/SX127x/SX127x.cpp | 11 +++++++++--
 src/modules/SX127x/SX127x.h   |  1 +
 5 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/TypeDef.h b/src/TypeDef.h
index aa4c41af..a2726ded 100644
--- a/src/TypeDef.h
+++ b/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
 
 /*!
diff --git a/src/modules/SX127x/SX1272.cpp b/src/modules/SX127x/SX1272.cpp
index ca1cc5a0..4cfa2e07 100644
--- a/src/modules/SX127x/SX1272.cpp
+++ b/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 {
diff --git a/src/modules/SX127x/SX1278.cpp b/src/modules/SX127x/SX1278.cpp
index 938118ac..ca0b8fab 100644
--- a/src/modules/SX127x/SX1278.cpp
+++ b/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 {
diff --git a/src/modules/SX127x/SX127x.cpp b/src/modules/SX127x/SX127x.cpp
index 0b877fd3..c6fa95a9 100644
--- a/src/modules/SX127x/SX127x.cpp
+++ b/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);
     }
 
diff --git a/src/modules/SX127x/SX127x.h b/src/modules/SX127x/SX127x.h
index f7f44166..27bf3f6c 100644
--- a/src/modules/SX127x/SX127x.h
+++ b/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();