accel: Fix accelerometer unit confusion

The original orientation code was based upon code that expected 1G to
roughly correspond to a reading of 256, to work-around the fact that the
input layer could not pass fractional values easily.

So the orientation_calc() code expected that too. But IIO readings after
scaling are properly in m/s², and our readings are integers.

We'll pass the scaling around to be applied at the last minute, when
doing calculations.

Closes: #100

src/drivers.h

@@ -40,6 +40,7 @@ typedef struct {
 	int accel_x;
 	int accel_y;
 	int accel_z;
+	gdouble scale;
 } AccelReadings;
 
 typedef struct {

src/drv-iio-buffer-accel.c

@@ -14,10 +14,6 @@
 #include <string.h>
 #include <errno.h>
 
-/* 1G (9.81m/s²) corresponds to "256"
- * value x scale is in m/s² */
-#define SCALE_TO_FF(scale) (scale * 256 / 9.81)
-
 typedef struct {
 	guint              timeout_id;
 	ReadingsUpdateFunc callback_func;
@@ -69,9 +65,10 @@ process_scan (IIOSensorData data, DrvData *or_data)
 	accel_y = -accel_y;
 
 	//FIXME report errors
-	readings.accel_x = accel_x * scale;
+	readings.accel_x = accel_x;
-	readings.accel_y = accel_y * scale;
+	readings.accel_y = accel_y;
-	readings.accel_z = accel_z * scale;
+	readings.accel_z = accel_z;
+	readings.scale = scale;
 	or_data->callback_func (&iio_buffer_accel, (gpointer) &readings, or_data->user_data);
 
 	return 1;

src/drv-iio-poll-accel.c

@@ -15,10 +15,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-/* 1G (9.81m/s²) corresponds to "256"
- * value x scale is in m/s² */
-#define SCALE_TO_FF(scale) (scale * 256 / 9.81)
-
 typedef struct DrvData {
 	guint               timeout_id;
 	ReadingsUpdateFunc  callback_func;
@@ -56,9 +52,10 @@ poll_orientation (gpointer user_data)
 	int accel_x, accel_y, accel_z;
 	AccelReadings readings;
 
-	accel_x = sysfs_get_int (data->dev, "in_accel_x_raw") * data->scale;
+	accel_x = sysfs_get_int (data->dev, "in_accel_x_raw");
-	accel_y = sysfs_get_int (data->dev, "in_accel_y_raw") * data->scale;
+	accel_y = sysfs_get_int (data->dev, "in_accel_y_raw");
-	accel_z = sysfs_get_int (data->dev, "in_accel_z_raw") * data->scale;
+	accel_z = sysfs_get_int (data->dev, "in_accel_z_raw");
+	readings.scale = data->scale;
 
 	//FIXME report errors
 	if (g_strcmp0 ("i2c-SMO8500:00", g_udev_device_get_sysfs_attr (data->dev, "name")) == 0) {
@@ -127,7 +124,7 @@ iio_poll_accel_open (GUdevDevice        *device,
 
 	drv_data->callback_func = callback_func;
 	drv_data->user_data = user_data;
-	drv_data->scale = SCALE_TO_FF(g_udev_device_get_sysfs_attr_as_double (device, "in_accel_scale"));
+	drv_data->scale = g_udev_device_get_sysfs_attr_as_double (device, "in_accel_scale");
 	if (drv_data->scale == 0.0)
 		drv_data->scale = 1.0;
 

src/drv-input-accel.c

@@ -76,6 +76,9 @@ accelerometer_changed (void)
 	readings.accel_x = accel_x;
 	readings.accel_y = accel_y;
 	readings.accel_z = accel_z;
+	/* Scale from 1G ~= 256 to a value in m/s² */
+	readings.scale = 1.0 / 256 * 9.81;
+
 	drv_data->callback_func (&input_accel, (gpointer) &readings, drv_data->user_data);
 }
 

src/iio-sensor-proxy.c

@@ -589,9 +589,10 @@ accel_changed_func (SensorDriver *driver,
 	OrientationUp orientation = data->previous_orientation;
 
 	//FIXME handle errors
-	g_debug ("Accel sent by driver (quirk applied): %d, %d, %d", readings->accel_x, readings->accel_y, readings->accel_z);
+	g_debug ("Accel sent by driver (quirk applied): %d, %d, %d (scale: %lf)",
+		 readings->accel_x, readings->accel_y, readings->accel_z, readings->scale);
 
-	orientation = orientation_calc (data->previous_orientation, readings->accel_x, readings->accel_y, readings->accel_z);
+	orientation = orientation_calc (data->previous_orientation, readings->accel_x, readings->accel_y, readings->accel_z, readings->scale);
 
 	data->accel_x = readings->accel_x;
 	data->accel_y = readings->accel_y;

src/orientation.c

@@ -56,12 +56,23 @@ string_to_orientation (const char *orientation)
 #define THRESHOLD_LANDSCAPE  35
 #define THRESHOLD_PORTRAIT  35
 
+/* First apply scale to get m/s², then
+ * convert to 1G ~= 256 as the code expects */
+#define SCALE(a) ((int) ((gdouble) a * scale * 256.0 / 9.81))
+
 OrientationUp
 orientation_calc (OrientationUp prev,
-                  int x, int y, int z)
+                  int in_x, int in_y, int in_z,
+                  gdouble scale)
 {
         int rotation;
         OrientationUp ret = prev;
+        int x, y, z;
+
+        /* this code expects 1G ~= 256 */
+        x = SCALE(in_x);
+        y = SCALE(in_y);
+        z = SCALE(in_z);
 
         /* Portrait check */
         rotation = round(atan((double) x / sqrt(y * y + z * z)) * RADIANS_TO_DEGREES);

src/orientation.h

@@ -30,4 +30,5 @@ OrientationUp  string_to_orientation (const char *orientation);
 OrientationUp  orientation_calc      (OrientationUp prev,
 				      int           x,
 				      int           y,
-				      int           z);
+				      int           z,
+				      gdouble       scale);