From 5e420e2adfc7913f289edceac32b0b73f86fe298 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Thu, 21 Mar 2019 17:48:40 +1100
Subject: [PATCH] AP_IneertialSensor: fixed startup race in SITL

---
 libraries/AP_InertialSensor/AP_InertialSensor.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libraries/AP_InertialSensor/AP_InertialSensor.cpp b/libraries/AP_InertialSensor/AP_InertialSensor.cpp
index 435258e2c3..6371a89c9e 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor.cpp
+++ b/libraries/AP_InertialSensor/AP_InertialSensor.cpp
@@ -1659,6 +1659,9 @@ AuxiliaryBus *AP_InertialSensor::get_auxiliary_bus(int16_t backend_id, uint8_t i
 void AP_InertialSensor::calc_vibration_and_clipping(uint8_t instance, const Vector3f &accel, float dt)
 {
     // check for clipping
+    if (_backends[instance] == nullptr) {
+        return;
+    }
     if (fabsf(accel.x) >  _backends[instance]->get_clip_limit() ||
         fabsf(accel.y) >  _backends[instance]->get_clip_limit() ||
         fabsf(accel.z) > _backends[instance]->get_clip_limit()) {