fix bad timestamp for API print event (#140)

* prevent latest timestamp from going back in time

It was possible for an analog message to enter the message processing queue and have its older timestamp assigned as the latest timestamp. If the timing was just right, this could occasionally cause the get_timestamp() function to produce an out of sequence/incorrect timestamp.

This commit fixes the problem by only updating the latest timestamp with the message's timestamp, if the message's timestamp is newer.

Author: alustig3

source/communication/pycboard.py

@@ -481,21 +481,23 @@ def process_data(self):
                     ID = int.from_bytes(content_bytes[:2], "little")
                     data = array(self.sm_info.analog_inputs[ID]["dtype"], content_bytes[2:])
                     content = (ID, data)
-                    message_sum = sum(message[:8]) + sum(data)
+                    msg_sum = sum(message[:8]) + sum(data)
                 else:
-                    message_sum = sum(message)
+                    msg_sum = sum(message)
                 # Process message.
-                if checksum == message_sum & 0xFFFF:  # Checksum OK.
-                    self.last_message_time = time.time()
-                    self.timestamp = int.from_bytes(message[:4], "little")
+                if checksum == (msg_sum & 0xFFFF):  # Checksum OK.
+                    msg_timestamp = int.from_bytes(message[:4], "little")
+                    if msg_timestamp > self.timestamp:
+                        self.last_message_time = time.time()
+                        self.timestamp = msg_timestamp
                     if msg_type in (MsgType.EVENT, MsgType.STATE):
                         content = int(content_bytes.decode())  # Event/state ID.
                     elif msg_type in (MsgType.PRINT, MsgType.WARNG):
                         content = content_bytes.decode()  # Print or error string.
                     elif msg_type == MsgType.VARBL:
                         content = content_bytes.decode()  # JSON string
                         self.sm_info.variables.update(json.loads(content))
-                    new_data.append(Datatuple(time=self.timestamp, type=msg_type, subtype=msg_subtype, content=content))
+                    new_data.append(Datatuple(time=msg_timestamp, type=msg_type, subtype=msg_subtype, content=content))
                 else:  # Bad checksum
                     new_data.append(
                         Datatuple(time=self.get_timestamp(), type=MsgType.WARNG, content="Bad data checksum.")
@@ -526,7 +528,7 @@ def trigger_event(self, event_name, source="u"):
     def get_timestamp(self):
         """Get the current pyControl timestamp in ms since start of framework run."""
         seconds_elapsed = time.time() - self.last_message_time
-        return self.timestamp + round(1000 * (seconds_elapsed))
+        return self.timestamp + round(1000 * seconds_elapsed)
 
     def send_serial_data(self, data, command, cmd_type=""):
         """Send data to the pyboard while framework is running."""