From 1103a3c842f2af9328b4fc79f7d52ca222ff2908 Mon Sep 17 00:00:00 2001
From: Risto <rotorman@users.noreply.github.com>
Date: Sun, 21 Nov 2021 23:09:47 +0100
Subject: [PATCH] Bluetooth trainer byte parsing: catch XOR state errors

In XOR state only 0x7E ^ 0x20 = 0x5E or 0x7D ^ 0x20 = 0x5D are expected.
Copy of my https://github.com/opentx/opentx/pull/8427
---
 radio/src/bluetooth.cpp | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/radio/src/bluetooth.cpp b/radio/src/bluetooth.cpp
index a6463f548..72aaab1d0 100644
--- a/radio/src/bluetooth.cpp
+++ b/radio/src/bluetooth.cpp
@@ -208,8 +208,22 @@ void Bluetooth::processTrainerByte(uint8_t data)
       break;
 
     case STATE_DATA_XOR:
-      appendTrainerByte(data ^ STUFF_MASK);
-      dataState = STATE_DATA_IN_FRAME;
+      switch (data) {
+        case BYTE_STUFF ^ STUFF_MASK:
+        case START_STOP ^ STUFF_MASK:
+          // Expected content, save the data
+          appendTrainerByte(data ^ STUFF_MASK);
+          dataState = STATE_DATA_IN_FRAME;
+          break;
+        case START_STOP:  // Illegal situation, as we have START_STOP, try to start from the beginning
+          bufferIndex = 0;
+          dataState = STATE_DATA_IN_FRAME;
+          break;
+        default:  
+          // Illegal situation, start looking for a new START_STOP byte
+          dataState = STATE_DATA_START;
+          break;
+      }
       break;
 
     case STATE_DATA_IDLE: