klippy: Support FIRMWARE_RESTART command

Add initial support for micro-controller resets via the Arduino reset
mechanism.  Also, automatically attempt a firmware restart if the
printer CRC does not match.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/serialhdl.py

@@ -3,7 +3,7 @@
 # Copyright (C) 2016  Kevin O'Connor <kevin@koconnor.net>
 #
 # This file may be distributed under the terms of the GNU GPLv3 license.
-import logging, threading
+import logging, threading, time
 import serial
 
 import msgproto, chelper, util
@@ -325,3 +325,16 @@ def stk500v2_leave(ser, reactor):
     res = ser.read(4096)
     logging.debug("Got %s from stk500v2" % (repr(res),))
     ser.baudrate = origbaud
+
+# Attempt an arduino style reset on a serial port
+def arduino_reset(serialport, reactor):
+    # First try opening the port at 1200 baud
+    ser = serial.Serial(serialport, 1200, timeout=0)
+    ser.read(1)
+    time.sleep(0.100)
+    # Then try toggling DTR
+    ser.dtr = True
+    time.sleep(0.100)
+    ser.dtr = False
+    time.sleep(0.100)
+    ser.close()