drivers/mma8652: convert raw data to milli g

drivers/include/mma8652.h

@@ -64,6 +64,7 @@ typedef struct {
     i2c_t i2c;              /**< I2C device, the accelerometer is connected to */
     uint8_t addr;           /**< the accelerometer's slave address on the I2C bus */
     bool initialized;       /**< accelerometer status, true if accelerometer is initialized */
+    int16_t scale;          /**< each count corresponds to (1/scale) g */
 } mma8652_t;
 
 /**
@@ -152,15 +153,15 @@ int mma8652_is_ready(mma8652_t *dev);
 
 /**
  * @brief Read accelerometer's data.
- * Acceleration can be calculated as:<br>
- *     \f$ a = \frac{value}{1024} \cdot g \f$ if full scale is set to 2g<br>
- *     \f$ a = \frac{value}{512} \cdot g \f$ if full scale is set to 4g<br>
- *     \f$ a = \frac{value}{256} \cdot g \f$ if full scale is set to 8g<br>
+ * Acceleration will be calculated as:<br>
+ *     \f$ a = \frac{value \cdot 1000}{1024} \cdot mg \f$ if full scale is set to 2g<br>
+ *     \f$ a = \frac{value \cdot 1000}{512} \cdot mg \f$ if full scale is set to 4g<br>
+ *     \f$ a = \frac{value \cdot 1000}{256} \cdot mg \f$ if full scale is set to 8g<br>
  *
  * @param[in]  dev          device descriptor of accelerometer
- * @param[out] x            x-axis value
- * @param[out] y            y-axis value
- * @param[out] z            z-axis value
+ * @param[out] x            x-axis value in mg
+ * @param[out] y            y-axis value in mg
+ * @param[out] z            z-axis value in mg
  * @param[out] status       accelerometer status register
  *
  * @return                  0 on success

drivers/mma8652/mma8652.c

@@ -97,6 +97,7 @@ int mma8652_init(mma8652_t *dev, i2c_t i2c, uint8_t address, uint8_t dr, uint8_t
     i2c_release(dev->i2c);
 
     dev->initialized = true;
+    dev->scale = 1024 >> range;
 
     return 0;
 }
@@ -216,9 +217,9 @@ int mma8652_read(mma8652_t *dev, int16_t *x, int16_t *y, int16_t *z, uint8_t *st
     i2c_release(dev->i2c);
 
     *status = buf[0];
-    *x = (int16_t)(((int16_t)buf[1] << 8) | buf[2]) / 16;
-    *y = (int16_t)(((int16_t)buf[3] << 8) | buf[4]) / 16;
-    *z = (int16_t)(((int16_t)buf[5] << 8) | buf[6]) / 16;
+    *x = (int32_t)((int16_t)(((int16_t)buf[1] << 8) | buf[2]) >> 4) * 1000 / dev->scale;
+    *y = (int32_t)((int16_t)(((int16_t)buf[3] << 8) | buf[4]) >> 4) * 1000 / dev->scale;
+    *z = (int32_t)((int16_t)(((int16_t)buf[5] << 8) | buf[6]) >> 4) * 1000 / dev->scale;
 
     return 0;
 }

tests/driver_mma8652/main.c

@@ -67,7 +67,7 @@ int main(void)
 
     while (1) {
         mma8652_read(&dev, &x, &y, &z, &status);
-        printf("Acceleration, raw: X: %d Y: %d Z: %d S: %2x\n", x, y, z, status);
+        printf("Acceleration, in mg: X: %d Y: %d Z: %d S: %2x\n", x, y, z, status);
         xtimer_usleep(SLEEP);
     }