+#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;
+static struct ao_quaternion ao_pad_orientation;
+#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 >> 9;
+ ao_ground_yaw = ao_sample_yaw_sum >> 9;
+ ao_ground_roll = ao_sample_roll_sum >> 9;
+ 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_orient = 0;
+
+ /* No rotation yet */
+ ao_quaternion_init_zero_rotation(&ao_rotation);
+
+ /* Take the pad IMU acceleration values and compute our current direction
+ */
+ ao_quaternion_init_vector(&ao_pad_orientation,
+ 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(&ao_pad_orientation,
+ &ao_pad_orientation);
+
+#endif
+ nsamples = 0;
+}
+
+#if HAS_GYRO
+static void
+ao_sample_rotate(void)
+{
+#ifdef AO_FLIGHT_TEST
+ float dt = (ao_sample_tick - ao_sample_prev_tick) / 100.0;
+#else
+ static const float dt = 1/100.0;
+#endif
+ float x = ao_mpu6000_gyro(ao_sample_pitch - ao_ground_pitch) * dt;
+ float y = ao_mpu6000_gyro(ao_sample_yaw - ao_ground_yaw) * dt;
+ float z = ao_mpu6000_gyro(ao_sample_roll - ao_ground_roll) * dt;
+
+ float n_2, n;
+ float s, c;
+
+ struct ao_quaternion rot;
+ struct ao_quaternion point;
+
+ /* The amount of rotation is just the length of the vector. Now,
+ * here's the trick -- assume that the rotation amount is small. In this case,
+ * sin(x) ≃ x, so we can just make this the sin.
+ */
+
+ n_2 = x*x + y*y + z*z;
+ n = sqrtf(n_2);
+ s = n / 2;
+ if (s > 1)
+ s = 1;
+ c = sqrtf(1 - s*s);
+
+ /* Make unit vector */
+ if (n > 0) {
+ x /= n;
+ y /= n;
+ z /= n;
+ }
+
+ /* Now compute the unified rotation quaternion */
+
+ ao_quaternion_init_rotation(&rot,
+ x, y, z,
+ s, c);
+
+ /* Integrate with the previous rotation amount */
+ ao_quaternion_multiply(&ao_rotation, &ao_rotation, &rot);
+
+ /* 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
+ */
+
+ ao_quaternion_rotate(&point, &ao_pad_orientation, &ao_rotation);
+
+ ao_orient = acosf(point.z) * (float) (180.0/M_PI);
+}
+#endif