From 83c632787325e3a4bd812f34b36f3794a5e8f00e Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Sat, 23 May 2020 14:38:00 +1000
Subject: [PATCH] AP_Compass: revert change to RM3100 scale factor and increase
 scale limit

This reverts the change from #13895 and instead resolves the issue by
increasing the scale factor limit to 1.4

There is an open question as to why some RM3100 compasses show a
different scale factor (by about 1.25 times) to other versions of the
same sensor. As we haven't resolved this properly it seems the correct
thing to do is follow the datasheet but allow for a wider range of
scale factors to cope with the variation between sensors
---
 libraries/AP_Compass/AP_Compass_Backend.h  | 3 +--
 libraries/AP_Compass/AP_Compass_RM3100.cpp | 7 ++++++-
 libraries/AP_Compass/CompassCalibrator.h   | 2 +-
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/libraries/AP_Compass/AP_Compass_Backend.h b/libraries/AP_Compass/AP_Compass_Backend.h
index e52ee2ea3d..a3e4545b74 100644
--- a/libraries/AP_Compass/AP_Compass_Backend.h
+++ b/libraries/AP_Compass/AP_Compass_Backend.h
@@ -58,8 +58,7 @@ public:
         DEVTYPE_MAG3110  = 0x0E,
         DEVTYPE_SITL  = 0x0F,
         DEVTYPE_IST8308 = 0x10,
-        DEVTYPE_RM3100_OLD = 0x11,
-        DEVTYPE_RM3100 = 0x12,
+        DEVTYPE_RM3100 = 0x11,
     };
 
 
diff --git a/libraries/AP_Compass/AP_Compass_RM3100.cpp b/libraries/AP_Compass/AP_Compass_RM3100.cpp
index c39cdd4b29..3b69a7c19c 100644
--- a/libraries/AP_Compass/AP_Compass_RM3100.cpp
+++ b/libraries/AP_Compass/AP_Compass_RM3100.cpp
@@ -135,7 +135,7 @@ bool AP_Compass_RM3100::init()
     dev->write_register(RM3100_CCZ1_REG, CCP1, true); // cycle count z
     dev->write_register(RM3100_CCZ0_REG, CCP0, true); // cycle count z
 
-    _scaler = (1 / GAIN_CC200) * UTESLA_TO_MGAUSS / 200.0; // has to be changed if using a different cycle count
+    _scaler = (1 / GAIN_CC200) * UTESLA_TO_MGAUSS; // has to be changed if using a different cycle count
 
     // lower retries for run
     dev->set_retries(3);
@@ -204,6 +204,11 @@ void AP_Compass_RM3100::timer()
     magy = ((uint32_t)data.magy_2 << 24) | ((uint32_t)data.magy_1 << 16) | ((uint32_t)data.magy_0 << 8);
     magz = ((uint32_t)data.magz_2 << 24) | ((uint32_t)data.magz_1 << 16) | ((uint32_t)data.magz_0 << 8);
 
+    // right-shift signed integer back to get correct measurement value
+    magx >>= 8;
+    magy >>= 8;
+    magz >>= 8;
+
     // apply scaler and store in field vector
     field(magx * _scaler, magy * _scaler, magz * _scaler);
 
diff --git a/libraries/AP_Compass/CompassCalibrator.h b/libraries/AP_Compass/CompassCalibrator.h
index e4b3774d9d..329596477e 100644
--- a/libraries/AP_Compass/CompassCalibrator.h
+++ b/libraries/AP_Compass/CompassCalibrator.h
@@ -7,7 +7,7 @@
 #define COMPASS_CAL_NUM_SAMPLES             300     // number of samples required before fitting begins
 
 #define COMPASS_MIN_SCALE_FACTOR 0.85
-#define COMPASS_MAX_SCALE_FACTOR 1.3
+#define COMPASS_MAX_SCALE_FACTOR 1.4
 
 class CompassCalibrator {
 public: