From 502b6ee0f73e55828086177a89f954253e7290cf Mon Sep 17 00:00:00 2001
From: DrZiplok <DrZiplok@f9c3cf11-9bcb-44bc-f272-b75c42450872>
Date: Sun, 17 Oct 2010 21:07:25 +0000
Subject: [PATCH] Teach the compass init code how to detect whether there is a
 compass present at all.  This lets systems where it's optional decide whether
 to try to use it or not...

git-svn-id: https://arducopter.googlecode.com/svn/trunk@684 f9c3cf11-9bcb-44bc-f272-b75c42450872
---
 libraries/APM_Compass/APM_Compass.cpp | 7 +++++--
 libraries/APM_Compass/APM_Compass.h   | 2 +-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/libraries/APM_Compass/APM_Compass.cpp b/libraries/APM_Compass/APM_Compass.cpp
index c04fd13997..71d72f5936 100644
--- a/libraries/APM_Compass/APM_Compass.cpp
+++ b/libraries/APM_Compass/APM_Compass.cpp
@@ -1,3 +1,4 @@
+// -*- tab-width: 4; Mode: C++; c-basic-offset: 3; indent-tabs-mode: t -*-
 /*
 	APM_Compass.cpp - Arduino Library for HMC5843 I2C Magnetometer
 	Code by Jordi Muņoz and Jose Julio. DIYDrones.com
@@ -78,7 +79,7 @@ APM_Compass_Class::APM_Compass_Class() : orientation(0), declination(0.0)
 }
 
 // Public Methods //////////////////////////////////////////////////////////////
-void APM_Compass_Class::Init(void)
+bool APM_Compass_Class::Init(void)
 {
   unsigned long currentTime = millis();  // record current time
   int numAttempts = 0;
@@ -102,7 +103,8 @@ void APM_Compass_Class::Init(void)
 	  Wire.beginTransmission(CompassAddress);
 	  Wire.send(ConfigRegA);
 	  Wire.send(PositiveBiasConfig);
-	  Wire.endTransmission();
+	  if (0 != Wire.endTransmission())
+		 continue;			// compass not responding on the bus
 	  delay(50);
 	  
 	  // set gains
@@ -146,6 +148,7 @@ void APM_Compass_Class::Init(void)
 	  Wire.endTransmission();                 // End transmission
 	  delay(50);
   }
+  return(success);
 }
 
 // Read Sensor data
diff --git a/libraries/APM_Compass/APM_Compass.h b/libraries/APM_Compass/APM_Compass.h
index f5d0ef3cf3..b6b11fde79 100644
--- a/libraries/APM_Compass/APM_Compass.h
+++ b/libraries/APM_Compass/APM_Compass.h
@@ -35,7 +35,7 @@ class APM_Compass_Class
 	unsigned long lastUpdate;	
 	
 	APM_Compass_Class();  // Constructor
-	void Init();
+	bool Init();
 	void Read();
 	void Calculate(float roll, float pitch);
 	void SetOrientation(int newOrientation);