Rover: Check all EKF cores for health on arming

APMrover2/AP_Arming.cpp

@@ -42,6 +42,18 @@ bool AP_Arming_Rover::pre_arm_rc_checks(const bool display_failure)
 // performs pre_arm gps related checks and returns true if passed
 bool AP_Arming_Rover::gps_checks(bool display_failure)
 {
+    const AP_AHRS &ahrs = AP::ahrs();
+
+    // always check if inertial nav has started and is ready
+    if (!ahrs.prearm_healthy()) {
+        const char *reason = ahrs.prearm_failure_reason();
+        if (reason == nullptr) {
+            reason = "AHRS not healthy";
+        }
+        check_failed(ARMING_CHECK_NONE, display_failure, "%s", reason);
+        return false;
+    }
+
     if (!rover.control_mode->requires_position() && !rover.control_mode->requires_velocity()) {
         // we don't care!
         return true;
@@ -55,7 +67,7 @@ bool AP_Arming_Rover::gps_checks(bool display_failure)
 
     // ensure position esetimate is ok
     if (!rover.ekf_position_ok()) {
-        const char *reason = AP::ahrs().prearm_failure_reason();
+        const char *reason = ahrs.prearm_failure_reason();
         if (reason == nullptr) {
             reason = "Need Position Estimate";
         }