Allow aligning the mag to any rotation

Introduce 3 new variables which allow setting the decidegrees
for the mag sensor alignment. When any of these 3 variables
are non-zero, mag is assumed to be mounted off-board and
"align_mag" as well as the board alignment are ignored.

Settings are named align_mag_roll, align_mag_pitch and
align_mag_yaw.

Fixes #86
Fixes #1029

src/main/fc/settings.yaml

@@ -264,6 +264,18 @@ groups:
         condition: USE_DUAL_MAG
         min: 0
         max: 1
+      - name: align_mag_roll
+        field: rollDeciDegrees
+        min: -1800
+        max: 3600
+      - name: align_mag_pitch
+        field: pitchDeciDegrees
+        min: -1800
+        max: 3600
+      - name: align_mag_yaw
+        field: yawDeciDegrees
+        min: -1800
+        max: 3600
 
   - name: PG_BAROMETER_CONFIG
     type: barometerConfig_t

src/main/sensors/compass.c

@@ -72,7 +72,10 @@ PG_RESET_TEMPLATE(compassConfig_t, compassConfig,
     .mag_hardware = MAG_HARDWARE_DEFAULT,
     .mag_declination = 0,
     .mag_to_use = 0,
-    .magCalibrationTimeLimit = 30
+    .magCalibrationTimeLimit = 30,
+    .rollDeciDegrees = 0,
+    .pitchDeciDegrees = 0,
+    .yawDeciDegrees = 0,
 );
 
 #ifdef USE_MAG
@@ -368,8 +371,34 @@ void compassUpdate(timeUs_t currentTimeUs)
         }
     }
 
-    applySensorAlignment(mag.magADC, mag.magADC, mag.dev.magAlign);
-    applyBoardAlignment(mag.magADC);
+    if (compassConfig()->rollDeciDegrees != 0 ||
+        compassConfig()->pitchDeciDegrees != 0 ||
+        compassConfig()->yawDeciDegrees != 0) {
+
+        // Externally aligned compass
+        struct fp_vector v = {
+            .X = mag.magADC[X],
+            .Y = mag.magADC[Y],
+            .Z = mag.magADC[Z],
+         };
+
+         fp_angles_t r = {
+             .angles.roll = DECIDEGREES_TO_RADIANS(compassConfig()->rollDeciDegrees),
+             .angles.pitch = DECIDEGREES_TO_RADIANS(compassConfig()->pitchDeciDegrees),
+             .angles.yaw = DECIDEGREES_TO_RADIANS(compassConfig()->yawDeciDegrees),
+         };
+
+         rotateV(&v, &r);
+
+         mag.magADC[X] = v.X;
+         mag.magADC[Y] = v.Y;
+         mag.magADC[Z] = v.Z;
+
+    } else {
+        // On-board compass
+        applySensorAlignment(mag.magADC, mag.magADC, mag.dev.magAlign);
+        applyBoardAlignment(mag.magADC);
+    }
 
     magUpdatedAtLeastOnce = 1;
 }

src/main/sensors/compass.h

@@ -52,13 +52,16 @@ typedef struct mag_s {
 extern mag_t mag;
 
 typedef struct compassConfig_s {
-    int16_t mag_declination;                // Get your magnetic decliniation from here : http://magnetic-declination.com/
+    int16_t mag_declination;                // Get your magnetic declination from here : http://magnetic-declination.com/
                                             // For example, -6deg 37min, = -637 Japan, format is [sign]dddmm (degreesminutes) default is zero.
-    sensor_align_e mag_align;               // mag alignment
+    sensor_align_e mag_align;               // on-board mag alignment. Ignored if externally aligned via *DeciDegrees.
     uint8_t mag_hardware;                   // Which mag hardware to use on boards with more than one device
     flightDynamicsTrims_t magZero;
     uint8_t mag_to_use;
     uint8_t magCalibrationTimeLimit;        // Time for compass calibration (seconds)
+    int16_t rollDeciDegrees;                // Alignment for external mag on the roll (X) axis (0.1deg)
+    int16_t pitchDeciDegrees;               // Alignment for external mag on the pitch (Y) axis (0.1deg)
+    int16_t yawDeciDegrees;                 // Alignment for external mag on the yaw (Z) axis (0.1deg)
 } compassConfig_t;
 
 PG_DECLARE(compassConfig_t, compassConfig);