From 518388c9c375045ec07bfbc3f7b207e0ad5fbeb9 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Tue, 7 Feb 2023 08:08:46 +1100
Subject: [PATCH] AP_RCProtocol: on IOMCU don't allow protocol to change once
 detected

this prevents a crash where in-flight noise causes an incorrect
protocol detection, such as DSM for a SBUS input
---
 libraries/AP_RCProtocol/AP_RCProtocol.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libraries/AP_RCProtocol/AP_RCProtocol.cpp b/libraries/AP_RCProtocol/AP_RCProtocol.cpp
index 8bd660bbf2..5e1ee3d5cd 100644
--- a/libraries/AP_RCProtocol/AP_RCProtocol.cpp
+++ b/libraries/AP_RCProtocol/AP_RCProtocol.cpp
@@ -72,6 +72,11 @@ bool AP_RCProtocol::should_search(uint32_t now_ms) const
     if (_detected_protocol != AP_RCProtocol::NONE && !rc().multiple_receiver_support()) {
         return false;
     }
+#else
+    // on IOMCU don't allow protocol to change once detected
+    if (_detected_protocol != AP_RCProtocol::NONE) {
+        return false;
+    }
 #endif
     return (now_ms - _last_input_ms >= 200);
 }