Improved handshake procedure on comm layer

"Hello" command sent to printer to trigger initial handshake can now be
configured. Commands that _always_ necessitate to be sent with checksum/
line number (e.g. M110 on Marlin) can be configured as such too.

Also fixed an issue causing the "Hello" command to not be actually enqueued
first thing on opening a connection. Seems to not have caused harm in the
wild, but was unintentional.

docs/configuration/config_yaml.rst

@@ -613,8 +613,30 @@ Use the following settings to configure the serial connection to the printer:
 
      # Use this to define additional baud rates to offer for connecting to serial ports. Must be a
      # valid integer. Defaults to not set
+     additionalBaudrates:
      - 123456
 
+     # Commands which are known to take a long time to be acknowledged by the firmware. E.g.
+     # homing, dwelling, auto leveling etc. Defaults to the below commands.
+     longRunningCommands:
+     - G4
+     - G28
+     - G29
+     - G30
+     - G32
+     - M400
+     - M226
+
+     # Commands which need to always be send with a checksum. Defaults to only M110
+     checksumRequiringCommands:
+     - M110
+
+     # Command to send in order to initiate a handshake with the printer.
+     # Defaults to "M110 N0" which simply resets the line numbers in the firmware and which
+     # should be acknowledged with a simple "ok".
+     helloCommand:
+     - M110 N0
+
 .. _sec-configuration-config_yaml-server:
 
 Server

src/octoprint/settings.py

@@ -84,7 +84,9 @@ default_settings = {
 		},
 		"additionalPorts": [],
 		"additionalBaudrates": [],
-		"longRunningCommands": ["G4", "G28", "G29", "G30", "G32", "M400", "M226"]
+		"longRunningCommands": ["G4", "G28", "G29", "G30", "G32", "M400", "M226"],
+		"checksumRequiringCommands": ["M110"],
+		"helloCommand": "M110 N0"
 	},
 	"server": {
 		"host": "0.0.0.0",

src/octoprint/util/comm.py

@@ -165,6 +165,8 @@ class MachineCom(object):
 
 		self._timeout = None
 
+		self._hello_command = settings().get(["serial", "helloCommand"])
+
 		self._alwaysSendChecksum = settings().getBoolean(["feature", "alwaysSendChecksum"])
 		self._sendChecksumWithUnknownCommands = settings().getBoolean(["feature", "sendChecksumWithUnknownCommands"])
 		self._unknownCommandsNeedAck = settings().getBoolean(["feature", "unknownCommandsNeedAck"])
@@ -175,6 +177,7 @@ class MachineCom(object):
 		self._lastResendNumber = None
 		self._currentResendCount = 0
 		self._resendSwallowNextOk = False
+		self._checksum_requiring_commands = settings().get(["serial", "checksumRequiringCommands"])
 
 		self._clear_to_send = CountedEvent(max=10, name="comm.clear_to_send")
 		self._send_queue = TypedQueue()
@@ -478,7 +481,7 @@ class MachineCom(object):
 	def fakeOk(self):
 		self._clear_to_send.set()
 
-	def sendCommand(self, cmd, cmd_type=None, processed=False):
+	def sendCommand(self, cmd, cmd_type=None, processed=False, force=False):
 		cmd = cmd.encode('ascii', 'replace')
 		if not processed:
 			cmd = process_gcode_line(cmd)
@@ -487,7 +490,7 @@ class MachineCom(object):
 
 		if self.isPrinting() and not self.isSdFileSelected():
 			self._commandQueue.put((cmd, cmd_type))
-		elif self.isOperational():
+		elif self.isOperational() or force:
 			self._sendCommand(cmd, cmd_type=cmd_type)
 
 	def sendGcodeScript(self, scriptName, replacements=None):
@@ -559,7 +562,7 @@ class MachineCom(object):
 
 			self._changeState(self.STATE_PRINTING)
 
-			self.sendCommand("M110 N0")
+			self.resetLineNumbers()
 
 			payload = {
 				"file": self._currentFile.getFilename(),
@@ -757,6 +760,16 @@ class MachineCom(object):
 		self._callback.on_comm_sd_state_change(self._sdAvailable)
 		self._callback.on_comm_sd_files(self._sdFiles)
 
+	def sayHello(self):
+		self.sendCommand(self._hello_command, force=True)
+		self._clear_to_send.set()
+
+	def resetLineNumbers(self, number=0):
+		if not self.isOperational():
+			return
+
+		self.sendCommand("M110 N%d" % number)
+
 	##~~ communication monitoring and handling
 
 	def _parseTemperatures(self, line):
@@ -865,10 +878,9 @@ class MachineCom(object):
 		connection_timeout = settings().getFloat(["serial", "timeout", "connection"])
 		detection_timeout = settings().getFloat(["serial", "timeout", "detection"])
 
-		# enqueue an M105 first thing
+		# enqueue the "hello command" first thing
 		if try_hello:
-			self._sendCommand("M110")
+			self.sayHello()
-			self._clear_to_send.set()
 
 		while self._monitoring_active:
 			try:
@@ -1089,8 +1101,7 @@ class MachineCom(object):
 							self._baudrateDetectRetry -= 1
 							self._serial.write('\n')
 							self._log("Baudrate test retry: %d" % (self._baudrateDetectRetry))
-							self._sendCommand("M110")
+							self.sayHello()
-							self._clear_to_send.set()
 						elif len(self._baudrateDetectList) > 0:
 							baudrate = self._baudrateDetectList.pop(0)
 							try:
@@ -1101,8 +1112,7 @@ class MachineCom(object):
 								self._baudrateDetectRetry = 5
 								self._timeout = get_new_timeout("communication")
 								self._serial.write('\n')
-								self._sendCommand("M110")
+								self.sayHello()
-								self._clear_to_send.set()
 							except:
 								self._log("Unexpected error while setting baudrate: %d %s" % (baudrate, get_exception_string()))
 						else:
@@ -1118,8 +1128,7 @@ class MachineCom(object):
 				elif self._state == self.STATE_CONNECTING:
 					if "start" in line and not startSeen:
 						startSeen = True
-						self._sendCommand("M110")
+						self.sayHello()
-						self._clear_to_send.set()
 					elif "ok" in line:
 						self._onConnected()
 					elif time.time() > self._timeout:
@@ -1241,6 +1250,8 @@ class MachineCom(object):
 
 		self._changeState(self.STATE_OPERATIONAL)
 
+		self.resetLineNumbers()
+
 		if self._sdAvailable:
 			self.refreshSdFiles()
 		else:
@@ -1588,7 +1599,11 @@ class MachineCom(object):
 							continue
 
 						# now comes the part where we increase line numbers and send stuff - no turning back now
-						if (gcode is not None or self._sendChecksumWithUnknownCommands) and (self.isPrinting() or self._alwaysSendChecksum):
+						command_requiring_checksum = gcode is not None and gcode in self._checksum_requiring_commands
+						command_allowing_checksum = gcode is not None or self._sendChecksumWithUnknownCommands
+						checksum_enabled = self.isPrinting() or self._alwaysSendChecksum
+
+						if command_requiring_checksum or (command_allowing_checksum and checksum_enabled):
 							linenumber = self._currentLine
 							self._addToLastLines(command)
 							self._currentLine += 1