AP_Compass: add expected DEV_ID parameters

libraries/AP_Compass/AP_Compass.cpp

@@ -453,6 +453,24 @@ const AP_Param::GroupInfo Compass::var_info[] = {
     // @Description: When enabled this will automatically check the orientation of compasses on successful completion of compass calibration. If set to 2 then external compasses will have their orientation automatically corrected.
     // @Values: 0:Disabled,1:CheckOnly,2:CheckAndFix
     AP_GROUPINFO("AUTO_ROT", 35, Compass, _rotate_auto, HAL_COMPASS_AUTO_ROT_DEFAULT),
+
+    // @Param: EXP_DID
+    // @DisplayName: Compass device id expected
+    // @Description: The expected value of COMPASS_DEV_ID, used by arming checks. Setting this to -1 means "don't care."
+    // @User: Advanced
+    AP_GROUPINFO("EXP_DID",  36, Compass, _state[0].expected_dev_id, -1),
+
+    // @Param: EXP_DID2
+    // @DisplayName: Compass2 device id expected
+    // @Description: The expected value of COMPASS_DEV_ID2, used by arming checks. Setting this to -1 means "don't care."
+    // @User: Advanced
+    AP_GROUPINFO("EXP_DID2", 37, Compass, _state[1].expected_dev_id, -1),
+
+    // @Param: EXP_DID3
+    // @DisplayName: Compass3 device id expected
+    // @Description: The expected value of COMPASS_DEV_ID3, used by arming checks. Setting this to -1 means "don't care."
+    // @User: Advanced
+    AP_GROUPINFO("EXP_DID3", 38, Compass, _state[2].expected_dev_id, -1),
     
     AP_GROUPEND
 };
@@ -1234,6 +1252,11 @@ bool Compass::configured(uint8_t i)
         return false;
     }
 
+    // if expected_dev_id is configured and the detected dev_id is different, return false
+    if (_state[i].expected_dev_id != -1 && _state[i].expected_dev_id != _state[i].dev_id) {
+        return false;
+    }
+
     // if we got here then it must be configured
     return true;
 }

libraries/AP_Compass/AP_Compass.h

@@ -431,6 +431,7 @@ private:
         // saved to eeprom when offsets are saved allowing ram &
         // eeprom values to be compared as consistency check
         AP_Int32    dev_id;
+        AP_Int32    expected_dev_id;
         int32_t detected_dev_id;
 
         AP_Int8     use_for_yaw;