+#if HAS_GYRO
+__pdata int32_t ao_sample_accel_along_sum;
+__pdata int32_t ao_sample_accel_across_sum;
+__pdata int32_t ao_sample_accel_through_sum;
+__pdata int32_t ao_sample_pitch_sum;
+__pdata int32_t ao_sample_yaw_sum;
+__pdata int32_t ao_sample_roll_sum;
+static struct ao_quaternion ao_rotation;
+#endif
+
+static void
+ao_sample_preflight_add(void)
+{
+#if HAS_ACCEL
+ ao_sample_accel_sum += ao_sample_accel;
+#endif
+ ao_sample_pres_sum += ao_sample_pres;
+#if HAS_GYRO
+ ao_sample_accel_along_sum += ao_sample_accel_along;
+ ao_sample_accel_across_sum += ao_sample_accel_across;
+ ao_sample_accel_through_sum += ao_sample_accel_through;
+ ao_sample_pitch_sum += ao_sample_pitch;
+ ao_sample_yaw_sum += ao_sample_yaw;
+ ao_sample_roll_sum += ao_sample_roll;
+#endif
+ ++nsamples;
+}
+
+static void
+ao_sample_preflight_set(void)
+{
+#if HAS_ACCEL
+ ao_ground_accel = ao_sample_accel_sum >> 9;
+ ao_sample_accel_sum = 0;
+#endif
+ ao_ground_pres = ao_sample_pres_sum >> 9;
+ ao_ground_height = pres_to_altitude(ao_ground_pres);
+ ao_sample_pres_sum = 0;
+#if HAS_GYRO
+ ao_ground_accel_along = ao_sample_accel_along_sum >> 9;
+ ao_ground_accel_across = ao_sample_accel_across_sum >> 9;
+ ao_ground_accel_through = ao_sample_accel_through_sum >> 9;
+ ao_ground_pitch = ao_sample_pitch_sum;
+ ao_ground_yaw = ao_sample_yaw_sum;
+ ao_ground_roll = ao_sample_roll_sum;
+ ao_sample_accel_along_sum = 0;
+ ao_sample_accel_across_sum = 0;
+ ao_sample_accel_through_sum = 0;
+ ao_sample_pitch_sum = 0;
+ ao_sample_yaw_sum = 0;
+ ao_sample_roll_sum = 0;
+ ao_sample_orient = 0;
+
+ struct ao_quaternion orient;
+
+ /* Take the pad IMU acceleration values and compute our current direction
+ */
+
+ ao_quaternion_init_vector(&orient,
+ (ao_ground_accel_across - ao_config.accel_zero_across),
+ (ao_ground_accel_through - ao_config.accel_zero_through),
+ (ao_ground_accel_along - ao_config.accel_zero_along));
+
+ ao_quaternion_normalize(&orient,
+ &orient);
+
+ /* Here's up */
+
+ struct ao_quaternion up = { .r = 0, .x = 0, .y = 0, .z = 1 };
+
+ if (ao_config.pad_orientation != AO_PAD_ORIENTATION_ANTENNA_UP)
+ up.z = -1;
+
+ /* Compute rotation to get from up to our current orientation, set
+ * that as the current rotation vector
+ */
+ ao_quaternion_vectors_to_rotation(&ao_rotation, &up, &orient);
+#endif
+ nsamples = 0;
+}
+
+#if HAS_GYRO
+
+#define TIME_DIV 200.0f
+
+static void
+ao_sample_rotate(void)
+{
+#ifdef AO_FLIGHT_TEST
+ float dt = (ao_sample_tick - ao_sample_prev_tick) / TIME_DIV;
+#else
+ static const float dt = 1/TIME_DIV;
+#endif
+ float x = ao_mpu6000_gyro((float) ((ao_sample_pitch << 9) - ao_ground_pitch) / 512.0f) * dt;
+ float y = ao_mpu6000_gyro((float) ((ao_sample_yaw << 9) - ao_ground_yaw) / 512.0f) * dt;
+ float z = ao_mpu6000_gyro((float) ((ao_sample_roll << 9) - ao_ground_roll) / 512.0f) * dt;
+ struct ao_quaternion rot;
+
+ ao_quaternion_init_half_euler(&rot, x, y, z);
+ ao_quaternion_multiply(&ao_rotation, &rot, &ao_rotation);
+
+ /* And normalize to make sure it remains a unit vector */
+ ao_quaternion_normalize(&ao_rotation, &ao_rotation);
+
+ /* Compute pitch angle from vertical by taking the pad
+ * orientation vector and rotating it by the current total
+ * rotation value. That will be a unit vector pointing along
+ * the airframe axis. The Z value will be the cosine of the
+ * change in the angle from vertical since boost.
+ *
+ * rot = ao_rotation * vertical * ao_rotation°
+ * rot = ao_rotation * (0,0,0,1) * ao_rotation°
+ * = ((a.z, a.y, -a.x, a.r) * (a.r, -a.x, -a.y, -a.z)) .z
+ *
+ * = (-a.z * -a.z) + (a.y * -a.y) - (-a.x * -a.x) + (a.r * a.r)
+ * = a.z² - a.y² - a.x² + a.r²
+ *
+ * rot = ao_rotation * (0, 0, 0, -1) * ao_rotation°
+ * = ((-a.z, -a.y, a.x, -a.r) * (a.r, -a.x, -a.y, -a.z)) .z
+ *
+ * = (a.z * -a.z) + (-a.y * -a.y) - (a.x * -a.x) + (-a.r * a.r)
+ * = -a.z² + a.y² + a.x² - a.r²
+ */
+
+ float rotz;
+ rotz = ao_rotation.z * ao_rotation.z - ao_rotation.y * ao_rotation.y - ao_rotation.x * ao_rotation.x + ao_rotation.r * ao_rotation.r;
+
+ ao_sample_orient = acosf(rotz) * (float) (180.0/M_PI);
+}
+#endif