axis: introduce steps_position_precision to motor controllers, and use it to...

axis: introduce steps_position_precision to motor controllers, and use it to determine delta in _get_motion

bliss/common/axis.py

@@ -1329,13 +1329,10 @@ class Axis:
 
     def _get_motion(self, user_target_pos):
         dial_target_pos = self.user2dial(user_target_pos)
-        delta = dial_target_pos - self.dial
-        if abs(delta) < 1e-6:
-            delta = 0.0
-
-        # check software limits
         target_pos = dial_target_pos * self.steps_per_unit
-        delta *= self.steps_per_unit
+        delta = target_pos - self.dial * self.steps_per_unit
+        if abs(delta) < self.controller.steps_position_precision(self):
+            delta = 0.0
         backlash = self.backlash / self.sign * self.steps_per_unit
         backlash_str = " (with %f backlash)" % self.backlash if backlash else ""
         low_limit_msg = "%s: move to `%f'%s would exceed low limit (%f)"
@@ -1344,13 +1341,14 @@ class Axis:
         low_limit = self.user2dial(user_low_limit) * self.steps_per_unit
         high_limit = self.user2dial(user_high_limit) * self.steps_per_unit
 
+        # check software limits
         if high_limit < low_limit:
             high_limit, low_limit = low_limit, high_limit
             user_high_limit, user_low_limit = user_low_limit, user_high_limit
             high_limit_msg, low_limit_msg = low_limit_msg, high_limit_msg
 
         if backlash:
-            if abs(delta) > 1e-6 and math.copysign(delta, backlash) != delta:
+            if abs(delta) > 0 and math.copysign(delta, backlash) != delta:
                 # move and backlash are not in the same direction;
                 # apply backlash correction, the move will happen
                 # in 2 steps

bliss/controllers/motor.py

@@ -114,6 +114,16 @@ class Controller:
     def config(self):
         return self.__config
 
+    def steps_position_precision(self, axis):
+        """
+        Return a float value representing the precision of the position in steps
+
+        * 1e-6 is the default value: it means the motor can deal with floating point
+        steps up to 6 digits 
+        * 1 means the motor controller can only deal with an integer number of steps
+        """
+        return 1e-6
+
     def check_limits(self, *axis_positions):
         """
         check limits for list of axis and positions

bliss/controllers/motors/icepap/__init__.py

@@ -115,6 +115,9 @@ class Icepap(Controller):
         if hasattr(axis, "_init_hardware"):
             axis._init_hardware()
 
+    def steps_position_precision(self, axis):
+        return 1
+
     # Axis power management
     def set_on(self, axis):
         """

bliss/controllers/motors/mockup.py

@@ -73,6 +73,10 @@ class Mockup(Controller):
         self.axis_settings.add("init_count", int)
         self.axis_settings.add("hw_position", float)
 
+    def steps_position_precision(self, axis):
+        """Mockup is really a stepper motor controller"""
+        return 1
+
     def read_hw_position(self, axis):
         return axis.settings.get("hw_position")