drivers: sensor: ams_as5600: Fix calculation of fractional part

commit 98903d4 upstream.

The original calculation has two bugs. One is the calculated value, and the
other is that the value is not in one-millionth parts.

What the original calculation does is compute a scaled position value by
multiplying the raw sensor value (`dev_data->position`) by
`AS5600_FULL_ANGLE`, which represents a full rotation in degrees. It then
subtracts the product of the whole number of pulses (`val->val1`) and
`AS5600_PULSES_PER_REV` from this scaled position value.

    ((int32_t)dev_data->position * AS5600_FULL_ANGLE)
    - (val->val1 * AS5600_PULSES_PER_REV);

What you actually need is to extract the fractional part of the value by
taking the modulo of AS5600_PULSES_PER_REV from the scaled value of the
position.

   (((int32_t)dev_data->position * AS5600_FULL_ANGLE)
   % AS5600_PULSES_PER_REV)

Then convert the value to one-millionth part.

   * (AS5600_MILLION_UNIT / AS5600_PULSES_PER_REV);

Signed-off-by: Yasushi SHOJI <[email protected]>

drivers/sensor/ams_as5600/ams_as5600.c

@@ -19,6 +19,7 @@ LOG_MODULE_REGISTER(ams_as5600, CONFIG_SENSOR_LOG_LEVEL);
 #define AS5600_ANGLE_REGISTER_H 0x0E
 #define AS5600_FULL_ANGLE		360
 #define AS5600_PULSES_PER_REV	4096
+#define AS5600_MILLION_UNIT	1000000
 
 struct as5600_dev_cfg {
 	struct i2c_dt_spec i2c_port;
@@ -60,8 +61,8 @@ static int as5600_get(const struct device *dev, enum sensor_channel chan,
 		val->val1 = ((int32_t)dev_data->position * AS5600_FULL_ANGLE) /
 							AS5600_PULSES_PER_REV;
 
-		val->val2 = ((int32_t)dev_data->position * AS5600_FULL_ANGLE) -
-					(val->val1 * AS5600_PULSES_PER_REV);
+		val->val2 = (((int32_t)dev_data->position * AS5600_FULL_ANGLE) %
+			     AS5600_PULSES_PER_REV) * (AS5600_MILLION_UNIT / AS5600_PULSES_PER_REV);
 	} else {
 		return -ENOTSUP;
 	}