fix issue #2463: initialize _set_position with controller value, even if read mode is "encoder"

bliss/common/axis.py

@@ -930,7 +930,12 @@ class Axis(Scannable):
         sp = self.settings.get("_set_position")
         if sp is not None:
             return sp
-        position = self.position
+        if self._read_position_mode == self.READ_POSITION_MODE.ENCODER:
+            # no setting, first time pos is read, init with controller hw pos.
+            # issue 2463
+            position = self._do_read_hw_position()
+        else:
+            position = self.position
         self._set_position = position
         return position
 
@@ -1087,7 +1092,10 @@ class Axis(Scannable):
     def _hw_position(self):
         if self._read_position_mode == self.READ_POSITION_MODE.ENCODER:
             return self.dial_measured_position
+        return self._do_read_hw_position()
 
+    @lazy_init
+    def _do_read_hw_position(self):
         try:
             curr_pos = self.__controller.read_position(self) / self.steps_per_unit
         except NotImplementedError:

tests/motors/test_encoder.py

@@ -63,6 +63,14 @@ def test_move(m1):
     assert m1.position == pytest.approx(m1.encoder.read())
 
 
+def test_issue_2463(default_session):
+    default_session.config.get_config("m1")["read_position"] = "encoder"
+    m1 = default_session.config.get("m1")
+
+    with mock.patch.object(m1.controller, "read_encoder", return_value=1000):
+        assert m1._set_position == 0
+
+
 def test_encoder_counter(default_session, m1, m1enc):
     s = scans.loopscan(3, 0.1, m1enc)
     assert numpy.array_equal(s.get_data()["m1enc"], [m1enc.read()] * 3)