Copter: do not adjust trims while landed

Closes #1282

Also cancels autotrim if you change modes, disarm the vehicle or land
again.

ArduCopter/Copter.h

@@ -473,6 +473,7 @@ private:
 
     // Used to exit the roll and pitch auto trim function
     uint8_t auto_trim_counter;
+    bool auto_trim_started = false;
 
     // Camera
 #if CAMERA == ENABLED
@@ -845,9 +846,10 @@ private:
     void winch_init();
     void winch_update();
 
-    // switches.cpp
+    // RC_Channel.cpp
     void save_trim();
     void auto_trim();
+    void auto_trim_cancel();
 
     // system.cpp
     void init_ardupilot() override;

ArduCopter/RC_Channel.cpp

@@ -580,14 +580,41 @@ void Copter::save_trim()
 
 // auto_trim - slightly adjusts the ahrs.roll_trim and ahrs.pitch_trim towards the current stick positions
 // meant to be called continuously while the pilot attempts to keep the copter level
+void Copter::auto_trim_cancel()
+{
+    auto_trim_counter = 0;
+    AP_Notify::flags.save_trim = false;
+    gcs().send_text(MAV_SEVERITY_INFO, "AutoTrim cancelled");
+}
+
 void Copter::auto_trim()
 {
     if (auto_trim_counter > 0) {
-        auto_trim_counter--;
+        if (copter.flightmode != &copter.mode_stabilize ||
+            !copter.motors->armed()) {
+            auto_trim_cancel();
+            return;
+        }
 
         // flash the leds
         AP_Notify::flags.save_trim = true;
 
+        if (!auto_trim_started) {
+            if (ap.land_complete) {
+                // haven't taken off yet
+                return;
+            }
+            auto_trim_started = true;
+        }
+
+        if (ap.land_complete) {
+            // landed again.
+            auto_trim_cancel();
+            return;
+        }
+
+        auto_trim_counter--;
+
         // calculate roll trim adjustment
         float roll_trim_adjustment = ToRad((float)channel_roll->get_control_in() / 4000.0f);
 
@@ -601,6 +628,7 @@ void Copter::auto_trim()
         // on last iteration restore leds and accel gains to normal
         if (auto_trim_counter == 0) {
             AP_Notify::flags.save_trim = false;
+            gcs().send_text(MAV_SEVERITY_INFO, "AutoTrim: Trims saved");
         }
     }
 }

ArduCopter/motors.cpp

@@ -52,7 +52,9 @@ void Copter::arm_motors_check()
 
         // arm the motors and configure for flight
         if (arming_counter == AUTO_TRIM_DELAY && motors->armed() && control_mode == Mode::Number::STABILIZE) {
+            gcs().send_text(MAV_SEVERITY_INFO, "AutoTrim start");
             auto_trim_counter = 250;
+            auto_trim_started = false;
             // ensure auto-disarm doesn't trigger immediately
             auto_disarm_begin = millis();
         }