From 1309b7332a47323949f23f87be1d13074fc267d2 Mon Sep 17 00:00:00 2001
From: James Bielman <jamesjb@galois.com>
Date: Fri, 4 Jan 2013 15:43:17 -0800
Subject: [PATCH] MPU6000: Use signed addition when accumulating readings.

- Fixes very erratic accel readings on the PX4 board.
---
 libraries/AP_InertialSensor/AP_InertialSensor_MPU6000.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_MPU6000.cpp b/libraries/AP_InertialSensor/AP_InertialSensor_MPU6000.cpp
index e824695152..b7016fad93 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_MPU6000.cpp
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_MPU6000.cpp
@@ -374,9 +374,9 @@ void AP_InertialSensor_MPU6000::_read_data_transaction() {
     memset(tx,0,15);
     tx[0] = MPUREG_ACCEL_XOUT_H | 0x80;
     _spi->transaction(tx, rx, 15);
-    
+
     for (uint8_t i = 0; i < 7; i++) {
-        _sum[i] += ((rx[2*i+1] << 8) | rx[2*i+2]);
+        _sum[i] += (int16_t)(((uint16_t)rx[2*i+1] << 8) | rx[2*i+2]);
     }   
     
     _count++;