ds402: Support checking the homing status. (#248)

Implement a new method BaseNode402.is_homed() which will switch to the
corresponding operation mode HOMING and then examine the Statusword
for the homing status bits.

This allows to skip the homing procedure in case the drive controller
still knows its position, but e.g. the Python application was
restarted.

Co-authored-by: André Filipe Silva <af-silva@users.noreply.github.com>

Author: acolomb

canopen/profiles/p402.py

@@ -274,6 +274,21 @@ def is_faulted(self):
         bitmask, bits = State402.SW_MASK['FAULT']
         return self.statusword & bitmask == bits
 
+    def is_homed(self, restore_op_mode=False):
+        """Switch to homing mode and determine its status."""
+        previous_op_mode = self.op_mode
+        if previous_op_mode != 'HOMING':
+            logger.info('Switch to HOMING from %s', previous_op_mode)
+            self.op_mode = 'HOMING'
+        homingstatus = None
+        for key, value in Homing.STATES.items():
+            bitmask, bits = value
+            if self.statusword & bitmask == bits:
+                homingstatus = key
+        if restore_op_mode:
+            self.op_mode = previous_op_mode
+        return homingstatus in ('TARGET REACHED', 'ATTAINED')
+
     def homing(self, timeout=TIMEOUT_HOMING_DEFAULT, set_new_home=True):
         """Function to execute the configured Homing Method on the node
         :param int timeout: Timeout value (default: 30)