From 3f4c5e243e050ac35c7703e1df5f1c2ad1b2bc2c Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Wed, 28 Sep 2022 13:26:27 +1000
Subject: [PATCH] AP_CANManager: disable SLCAN when armed

this disables SLCAN if enabled using CAN_SLCAN_CPORT and
SERIALn_PROTOCOL=22 when we are armed, to reduce load on the CAN
thread from the very inefficient SLCAN processing
---
 libraries/AP_CANManager/AP_SLCANIface.cpp | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/libraries/AP_CANManager/AP_SLCANIface.cpp b/libraries/AP_CANManager/AP_SLCANIface.cpp
index da89d24937..8688ae6507 100644
--- a/libraries/AP_CANManager/AP_SLCANIface.cpp
+++ b/libraries/AP_CANManager/AP_SLCANIface.cpp
@@ -511,12 +511,17 @@ inline void SLCAN::CANIface::addByte(const uint8_t byte)
 
 void SLCAN::CANIface::update_slcan_port()
 {
+    const bool armed = hal.util->get_soft_armed();
     if (_set_by_sermgr) {
-        // Once we pick SerialManager path we hold on 
-        // to that until reboot
+        if (armed && _port != nullptr) {
+            // auto-disable when armed
+            _port->lock_port(0, 0);
+            _port = nullptr;
+            _set_by_sermgr = false;
+        }
         return;
     }
-    if (_port == nullptr) {
+    if (_port == nullptr && !armed) {
          _port = AP::serialmanager().find_serial(AP_SerialManager::SerialProtocol_SLCAN, 0);
         if (_port != nullptr) {
             _port->lock_port(_serial_lock_key, _serial_lock_key);