modbus_tk.patch

--- modbus-tk-dist/modbus_tk/modbus.py	2018-02-19 12:32:57.786042390 +0100
+++ modbus/modbus-tk/modbus_tk/modbus.py	2018-02-22 10:47:44.106280248 +0100
@@ -175,7 +175,7 @@
             if expected_length < 0:
                 # No length was specified and calculated length can be used:
                 # slave + func + bytcodeLen + bytecode x 2 + crc1 + crc2
-                expected_length = 2 * quantity_of_x + 5
+                expected_length = 2 * quantity_of_x + 6
 
         elif (function_code == defines.WRITE_SINGLE_COIL) or (function_code == defines.WRITE_SINGLE_REGISTER):
             if function_code == defines.WRITE_SINGLE_COIL:
@@ -289,7 +289,6 @@
             request = retval
         if self._verbose:
             LOGGER.debug(get_log_buffer("-> ", request))
-            print("Expect bytes: %i" % expected_length )
         self._send(request)
 
         call_hooks("modbus.Master.after_send", (self, ))
@@ -302,13 +301,24 @@
                 response = retval
             if self._verbose:
                 LOGGER.debug(get_log_buffer("<- ", response))
+                _deb= ""
+                buff = bytearray(response[0:])
+                for i in buff:
+                  _deb += '{0:02x}'.format(int(i)) + "-"
+                print("DEBUG: Values in hex " + _deb )
+
+            # My adapter suddenly started receiving a leading '0' 
+            #  - can't be bothered to figure out why
+            #  - it happened after playing with FTDI direct drivers
+            #  - so, we'll just drop it
+            if response[0] == b'\x00':
+              response = response[1:]
+              if self._verbose:
+                print("Dropping leading 0")
 
             # extract the pdu part of the response
             response_pdu = query.parse_response(response)
 
-            if self._verbose:
-                LOGGER.debug(get_log_buffer("<- ", response_pdu))
-
             # analyze the received data
             (return_code, byte_2) = struct.unpack(">BB", response_pdu[0:2])