pybricks.common.Control: Restore arg order.

The integral_range argument was dropped in
3f0042f.

While this setting was virtually never used, the pid()
method is used in some example projects. Typically, all 5 parameters
are unpacked to easily read the existing PID parameters. Removing one
argument would break these projects.

This commit restores the order and number of arguments to avoid a
breaking change. The setting may be reserved for future use instead.

CHANGELOG.md

@@ -4,6 +4,15 @@
 
 ## [Unreleased]
 
+### Changed:
+- Dropped `integral_range` argument from `Control.pid()`. This setting was
+  ineffective and never used. When set incorrectly, the motor could get stuck
+  for certain combinations of `kp` and `ki`.
+- Improved motor behavior for cases with low-speed, low-load, but high
+  inertia. ([support#366])
+
+[support#366]: https://github.com/pybricks/support/issues/366
+
 ## [3.1.0b1] - 2021-08-21
 
 ### Added

pybricks/common/pb_type_control.c

@@ -96,6 +96,7 @@ STATIC mp_obj_t common_Control_pid(size_t n_args, const mp_obj_t *pos_args, mp_m
         PB_ARG_DEFAULT_NONE(kp),
         PB_ARG_DEFAULT_NONE(ki),
         PB_ARG_DEFAULT_NONE(kd),
+        PB_ARG_DEFAULT_NONE(reserved),
         PB_ARG_DEFAULT_NONE(integral_rate));
 
     // Read current values
@@ -104,14 +105,16 @@ STATIC mp_obj_t common_Control_pid(size_t n_args, const mp_obj_t *pos_args, mp_m
     pbio_control_settings_get_pid(&self->control->settings, &kp, &ki, &kd, &integral_rate);
 
     // If all given values are none, return current values
+    (void)reserved_in;
     if (kp_in == mp_const_none && ki_in == mp_const_none && kd_in == mp_const_none &&
         integral_rate_in == mp_const_none) {
-        mp_obj_t ret[4];
+        mp_obj_t ret[5];
         ret[0] = mp_obj_new_int(kp);
         ret[1] = mp_obj_new_int(ki);
         ret[2] = mp_obj_new_int(kd);
-        ret[3] = mp_obj_new_int(integral_rate);
-        return mp_obj_new_tuple(4, ret);
+        ret[3] = mp_const_none;
+        ret[4] = mp_obj_new_int(integral_rate);
+        return mp_obj_new_tuple(5, ret);
     }
 
     // Assert control is not active