Merge pull request #173 from Sandyman/master

Allow for timestamps of other types than float

Author: christiansandberg

canopen/pdo/base.py

@@ -174,7 +174,7 @@ def __init__(self, pdo_node, com_record, map_array):
         #: Current message data
         self.data = bytearray()
         #: Timestamp of last received message
-        self.timestamp = 0
+        self.timestamp = None
         #: Period of receive message transmission in seconds
         self.period = None
         self.callbacks = []
@@ -268,7 +268,8 @@ def on_message(self, can_id, data, timestamp):
             with self.receive_condition:
                 self.is_received = True
                 self.data = data
-                self.period = timestamp - self.timestamp
+                if self.timestamp is not None:
+                    self.period = timestamp - self.timestamp
                 self.timestamp = timestamp
                 self.receive_condition.notify_all()
                 for callback in self.callbacks: