pbio/drivebase: Fix order of passive actuation.

If passive actuation is required at the end of a
maneuver (brake or coast), this stops control
automatically.

Changing integration states at that point is
not a valid operation, so we need to put this
after the return on passive actuation.

This fixes coast and brake not working on
drivebases.

Author: laurensvalk

CHANGELOG.md

@@ -11,6 +11,7 @@
 ### Fixed
 - Fixed direction for `DriveBase.turn()` and `Drivebase.curve()` for some
   arguments ([support#535]).
+- Fixed `then=Stop.COAST` not working in `DriveBase` methods ([support#535]).
 
 [support#535]: https://github.com/pybricks/support/issues/535
 [support#536]: https://github.com/pybricks/support/issues/536

lib/pbio/src/drivebase.c

@@ -239,6 +239,15 @@ pbio_error_t pbio_drivebase_update(pbio_drivebase_t *db) {
     pbio_control_update(&db->control_distance, time_now, &state_distance, &ref_distance, &sum_actuation, &sum_torque);
     pbio_control_update(&db->control_heading, time_now, &state_heading, &ref_heading, &dif_actuation, &dif_torque);
 
+    // If either controller coasts, coast both, thereby also stopping control.
+    if (sum_actuation == PBIO_ACTUATION_COAST || dif_actuation == PBIO_ACTUATION_COAST) {
+        return pbio_drivebase_actuate(db, PBIO_ACTUATION_COAST, 0, 0);
+    }
+    // If either controller brakes, brake both, thereby also stopping control.
+    if (sum_actuation == PBIO_ACTUATION_BRAKE || dif_actuation == PBIO_ACTUATION_BRAKE) {
+        return pbio_drivebase_actuate(db, PBIO_ACTUATION_BRAKE, 0, 0);
+    }
+
     // The leading controller is able to pause when it stalls. The following controller does not do its own stall,
     // but follows the leader. This ensures they complete at exactly the same time.
 
@@ -254,15 +263,6 @@ pbio_error_t pbio_drivebase_update(pbio_drivebase_t *db) {
         return err;
     }
 
-    // If either controller coasts, coast both
-    if (sum_actuation == PBIO_ACTUATION_COAST || dif_actuation == PBIO_ACTUATION_COAST) {
-        return pbio_drivebase_actuate(db, PBIO_ACTUATION_COAST, 0, 0);
-    }
-    // If either controller brakes, brake both
-    if (sum_actuation == PBIO_ACTUATION_BRAKE || dif_actuation == PBIO_ACTUATION_BRAKE) {
-        return pbio_drivebase_actuate(db, PBIO_ACTUATION_BRAKE, 0, 0);
-    }
-
     // The left servo drives at a torque and speed of sum / 2 + dif / 2
     int32_t feed_forward_left = pbio_observer_get_feedforward_torque(&db->left->observer, ref_distance.rate / 2 + ref_heading.rate / 2, ref_distance.acceleration / 2 + ref_heading.acceleration / 2);
     err = pbio_servo_actuate(db->left, sum_actuation, sum_torque / 2 + dif_torque / 2 + feed_forward_left);