step_size instead of speed_factor

no longer need to pre configure a speed_factor,
the proper units of speed and accel are taken from
the hardware

secop_psi/phytron.py

@@ -37,7 +37,7 @@ class PhytronIO(StringIO):
     def communicate(self, command, expect_response=True):
         for ntry in range(5, 0, -1):
             try:
-                head, _, reply = super().communicate('\x02' + command).partition('\x02')
+                _, _, reply = super().communicate('\x02' + command).partition('\x02')
                 if reply[0] == '\x06':  # ACK
                     if len(reply) == 1 and expect_response:
                         raise CommunicationFailedError('empty response')
@@ -53,7 +53,6 @@ class PhytronIO(StringIO):
 class Motor(PersistentMixin, HasIO, Drivable):
     axis = Property('motor axis X or Y', StringType(), default='X')
     address = Property('address', IntRange(0, 15), default=0)
-    speed_factor = Property('steps / degree', FloatRange(0, None), default=2000)
 
     encoder_mode = Parameter('how to treat the encoder', EnumType('encoder', NO=0, READ=1, CHECK=2),
                              default=1, readonly=False)
@@ -78,6 +77,7 @@ class Motor(PersistentMixin, HasIO, Drivable):
     _backlash_pending = False
     _mismatch_count = 0
     _rawlimits = None
+    _step_size = None
 
     def earlyInit(self):
         super().earlyInit()
@@ -147,29 +147,39 @@ class Motor(PersistentMixin, HasIO, Drivable):
             return self.value
         return float(self.get('P22R')) * self.sign - self.offset
 
+    def write_sign(self, value):
+        self.sign = value
+        self.saveParameters()
+        return Done
+
+    def get_step_size(self):
+        self._step_size = float(self.get('P03R'))
+
     def read_speed(self):
-        return float(self.get('P14R')) / self.speed_factor
+        if self._step_size is None:
+            # avoid repeatedly reading step size, as this is polled and will not change
+            self.get_step_size()
+        return float(self.get('P14R')) * self._step_size
 
     def write_speed(self, value):
-        inv_factor = float(self.get('P03R'))
+        self.get_step_size()  # read step size anyway, it does not harm
-        if abs(inv_factor * self.speed_factor - 1) > 0.001:
+        return float(self.set_get('P14S', round(value / self._step_size), 'P14R')) * self._step_size
-            raise HardwareError('speed factor does not match %g' % (1.0 / inv_factor))
-        return float(self.set_get('P14S', int(value * self.speed_factor), 'P14R')) / self.speed_factor
 
     def read_accel(self):
-        return float(self.get('P15R')) / self.speed_factor
+        if not self._step_size:
+            self.get_step_size()
+        return float(self.get('P15R')) * self._step_size
 
     def write_accel(self, value):
-        if abs(float(self.get('P03R')) * self.speed_factor - 1) > 0.001:
+        self.get_step_size()
-            raise HardwareError('speed factor does not match')
+        return float(self.set_get('P15S', round(value / self._step_size), 'P15R')) * self._step_size
-        return float(self.set_get('P15S', int(value * self.speed_factor), 'P15R')) / self.speed_factor
 
     def _check_limits(self, *values):
         for name, (mn, mx) in ('user', self._rawlimits), ('abs', self.abslimits):
             mn -= self.offset
             mx -= self.offset
             for v in values:
-                if not (mn <= v <= mx):
+                if not mn <= v <= mx:
                     raise BadValueError('%s limits violation: %g <= %g <= %g' % (name, mn, v, mx))
                 v += self.offset