diff --git a/docs/configuration/config_yaml.rst b/docs/configuration/config_yaml.rst
index 11981684..c8640400 100644
--- a/docs/configuration/config_yaml.rst
+++ b/docs/configuration/config_yaml.rst
@@ -373,10 +373,18 @@ Use the following settings to enable or disable OctoPrint features:
      # during connect.
      waitForStartOnConnect: false
 
-     # Specifies whether OctoPrint should send linenumber + checksum with every command. Needed for
+     # Specifies whether OctoPrint should send linenumber + checksum with every printer command. Needed for
      # successful communication with Repetier firmware
      alwaysSendChecksum: false
 
+     # Specifies whether OctoPrint should also send linenumber + checksum with commands that are *not*
+     # detected as valid GCODE (as in, they do not match the regular expression "^\s*([GM]\d+|T)").
+     sendChecksumWithUnknownCommands: false
+
+     # Specifies whether OctoPrint should also use up acknowledgments ("ok") for commands that are *not*
+     # detected as valid GCODE (as in, they do not match the regular expression "^\s*([GM]\d+|T)").
+     unknownCommandsNeedAck: false
+
      # Whether to ignore the first ok after a resend response. Needed for successful communication with
      # Repetier firmware
      swallowOkAfterResend: false
diff --git a/src/octoprint/plugins/virtual_printer/virtual.py b/src/octoprint/plugins/virtual_printer/virtual.py
index 8f54cb28..a94afa93 100644
--- a/src/octoprint/plugins/virtual_printer/virtual.py
+++ b/src/octoprint/plugins/virtual_printer/virtual.py
@@ -149,6 +149,11 @@ class VirtualPrinter():
 				self._sendOk()
 				continue
 
+			if data.strip() == "version":
+				from octoprint._version import get_versions
+				self.outgoing.put("OctoPrint VirtualPrinter v" + get_versions()["version"])
+				continue
+
 			if len(data.strip()) > 0 and self._okBeforeCommandOutput:
 				self._sendOk()
 
@@ -394,7 +399,6 @@ class VirtualPrinter():
 				pass
 
 		if tool >= settings().getInt(["devel", "virtualPrinter", "numExtruders"]):
-			self._sendOk()
 			return
 
 		try:
@@ -406,7 +410,6 @@ class VirtualPrinter():
 			self._waitForHeatup("tool%d" % tool)
 		if settings().getBoolean(["devel", "virtualPrinter", "repetierStyleTargetTemperature"]):
 			self.outgoing.put("TargetExtr%d:%d" % (tool, self.targetTemp[tool]))
-		self._sendOk()
 
 	def _parseBedCommand(self, line):
 		try:
@@ -418,7 +421,6 @@ class VirtualPrinter():
 			self._waitForHeatup("bed")
 		if settings().getBoolean(["devel", "virtualPrinter", "repetierStyleTargetTemperature"]):
 			self.outgoing.put("TargetBed:%d" % self.bedTargetTemp)
-		self._sendOk()
 
 	def _performMove(self, line):
 		matchX = re.search("X([0-9.]+)", line)
diff --git a/src/octoprint/settings.py b/src/octoprint/settings.py
index 8257cb6a..331b3e8f 100644
--- a/src/octoprint/settings.py
+++ b/src/octoprint/settings.py
@@ -132,6 +132,8 @@ default_settings = {
 		"temperatureGraph": True,
 		"waitForStartOnConnect": False,
 		"alwaysSendChecksum": False,
+		"sendChecksumWithUnknownCommands": False,
+		"unknownCommandsNeedAck": False,
 		"sdSupport": True,
 		"sdAlwaysAvailable": False,
 		"swallowOkAfterResend": True,
diff --git a/src/octoprint/util/comm.py b/src/octoprint/util/comm.py
index f1155bb1..13bbd783 100644
--- a/src/octoprint/util/comm.py
+++ b/src/octoprint/util/comm.py
@@ -155,6 +155,8 @@ class MachineCom(object):
 		self._timeout = None
 
 		self._alwaysSendChecksum = settings().getBoolean(["feature", "alwaysSendChecksum"])
+		self._sendChecksumWithUnknownCommands = settings().getBoolean(["feature", "sendChecksumWithUnknownCommands"])
+		self._unknownCommandsNeedAck = settings().getBoolean(["feature", "unknownCommandsNeedAck"])
 		self._currentLine = 1
 		self._resendDelta = None
 		self._lastLines = deque([], 50)
@@ -1498,6 +1500,9 @@ class MachineCom(object):
 				# fetch command and optional linenumber from queue
 				command, linenumber, _ = entry
 
+				# some firmwares (e.g. Smoothie) might support additional in-band communication that will not
+				# stick to the acknowledgement behaviour of GCODE, so we check here if we have a GCODE command
+				# at hand here and only clear our clear_to_send flag later if that's the case
 				gcode_match = self._regex_command.search(command)
 				is_gcode = gcode_match is not None
 
@@ -1509,7 +1514,7 @@ class MachineCom(object):
 					# line number predetermined, use that
 					self._doSendWithChecksum(command, linenumber)
 				else:
-					if self.isPrinting() or self._alwaysSendChecksum:
+					if (is_gcode or self._sendChecksumWithUnknownCommands) and (self.isPrinting() or self._alwaysSendChecksum):
 						linenumber = self._currentLine
 						self._addToLastLines(command)
 						self._currentLine += 1
@@ -1517,12 +1522,17 @@ class MachineCom(object):
 					else:
 						self._doSendWithoutChecksum(command)
 
+				use_up_clear = not self._unknownCommandsNeedAck
 				if is_gcode:
-					# trigger "sent" phase
+					# trigger "sent" phase and use up one "ok"
 					self._process_command_phase("sent", command, gcode=gcode_match.group(1))
+					use_up_clear = True
+
+				# if we need to use up a clear, do that now
+				if use_up_clear:
+					self._clear_to_send.clear()
 
 				# wait for the next clear
-				self._clear_to_send.clear()
 				self._clear_to_send.wait()
 			except:
 				self._logger.exception("Caught an exception in the send loop")