diff --git a/awlsim-test b/awlsim-test
index f8c90dd79..b12945b5e 100755
--- a/awlsim-test
+++ b/awlsim-test
@@ -110,7 +110,8 @@ def usage():
 def writeStdout(message):
 	if Logging.loglevel >= Logging.LOG_INFO:
 		sys.stdout.write(message)
-		sys.stdout.flush()
+		if not isMicroPython:
+			sys.stdout.flush()
 
 nextScreenUpdate = 0.0
 lastDump = ""
diff --git a/awlsim/common/compat.py b/awlsim/common/compat.py
index 31a54e69f..f8b9d1907 100644
--- a/awlsim/common/compat.py
+++ b/awlsim/common/compat.py
@@ -241,3 +241,13 @@ def __exit__(self, *unused):
 		lambda d: d.keys())
 dictValues = py23(lambda d: d.viewvalues(),
 		  lambda d: d.values())
+
+if isMicroPython: #@nocov
+	import select
+	if not hasattr(select, "select"):
+		select.select = None # Dummy
+
+	try:
+		IOError
+	except NameError:
+		IOError = OSError
diff --git a/awlsim/common/dynamic_import.py b/awlsim/common/dynamic_import.py
index eb701af41..1b834b12d 100644
--- a/awlsim/common/dynamic_import.py
+++ b/awlsim/common/dynamic_import.py
@@ -37,10 +37,13 @@ def importModule(moduleName):
 	May raise importError."""
 
 	import awlsim_loader.cython_helper as cython_helper
-	try:
-		import importlib
-	except ImportError as e: #@nocov
+	if isMicroPython:
 		importlib = None
+	else:
+		try:
+			import importlib
+		except ImportError as e: #@nocov
+			importlib = None
 
 	# If we are running in cython module,
 	# translate the moduleName to its cython name.
diff --git a/awlsim/common/util.py b/awlsim/common/util.py
index de54b42d1..b4bdb334c 100644
--- a/awlsim/common/util.py
+++ b/awlsim/common/util.py
@@ -129,7 +129,8 @@ def __print(cls, stream, text):
 				stream.write("[%.3f] " % cls._getUptime())
 				stream.write(text)
 				stream.write("\n")
-				stream.flush()
+				if not isMicroPython:
+					stream.flush()
 
 	@classmethod
 	def printDebug(cls, text): #@nocov
@@ -188,7 +189,6 @@ def safeFileRead(filename):
 	try:
 		with open(filename, "rb") as fd:
 			data = fd.read()
-			fd.close()
 	except IOError as e: #@nocov
 		raise AwlSimError("Failed to read '%s': %s" %\
 			(filename, str(e)))
@@ -206,7 +206,6 @@ def safeFileWrite(filename, data):
 		with open(tmpFile, "wb") as fd:
 			fd.write(data)
 			fd.flush()
-			fd.close()
 		if not osIsPosix: #@nocov
 			# Can't use safe rename on non-POSIX.
 			# Must unlink first.
diff --git a/awlsim/core/systemblocks/tables.py b/awlsim/core/systemblocks/tables.py
index fa0a603b4..f0087dc22 100644
--- a/awlsim/core/systemblocks/tables.py
+++ b/awlsim/core/systemblocks/tables.py
@@ -23,8 +23,8 @@
 #from awlsim.common.cython_support cimport * #@cy
 from awlsim.common.compat import *
 
-from awlsim.core.systemblocks.system_sfb import * #+cimport
-from awlsim.core.systemblocks.system_sfc import * #+cimport
+from awlsim.core.systemblocks.system_sfc import _SFC_table #+cimport
+from awlsim.core.systemblocks.system_sfb import _SFB_table #+cimport
 
 __all__ = [
 	"SFC_table",
diff --git a/awlsim/coreserver/messages.py b/awlsim/coreserver/messages.py
index 0002b85be..fe728bbaa 100644
--- a/awlsim/coreserver/messages.py
+++ b/awlsim/coreserver/messages.py
@@ -702,11 +702,11 @@ def fromBytes(cls, payload):
 class AwlSimMessage_BUILD(AwlSimMessage):
 	msgId = AwlSimMessage.MSG_ID_BUILD
 
-	plStruct = struct.Struct(str(">32x"))
+	plStruct = struct.Struct(str(">8I"))
 
 	def toBytes(self):
 		try:
-			pl = self.plStruct.pack()
+			pl = self.plStruct.pack(0, 0, 0, 0, 0, 0, 0, 0)
 			return AwlSimMessage.toBytes(self, len(pl)) + pl
 		except (ValueError, struct.error) as e:
 			raise TransferError("BUILD: Invalid data format")
@@ -1536,14 +1536,14 @@ class AwlSimMessage_IDENTS(AwlSimMessage):
 	#	reserved (32 bit)
 	#	reserved (32 bit)
 	#	reserved (32 bit)
-	plHdrStruct = struct.Struct(str(">6I40x"))
+	plHdrStruct = struct.Struct(str(">16I"))
 
 	# Payload module header struct:
 	#	Number of parameters (32 bit)
 	#	reserved (32 bit)
 	#	reserved (32 bit)
 	#	reserved (32 bit)
-	plModStruct = struct.Struct(str(">I12x"))
+	plModStruct = struct.Struct(str(">4I"))
 
 	# awlSources: List of AwlSource()s
 	# symTabSources: List of SymTabSource()s
@@ -1563,7 +1563,9 @@ def toBytes(self):
 						  len(self.hwMods),
 						  len(self.libSelections),
 						  len(self.fupSources),
-						  len(self.kopSources)) ]
+						  len(self.kopSources),
+						  0, 0, 0, 0, 0,
+						  0, 0, 0, 0, 0) ]
 		def addSrcs(srcs):
 			for src in srcs:
 				payload.append(self.packString(src.name))
@@ -1573,7 +1575,7 @@ def addSrcs(srcs):
 		addSrcs(self.symTabSources)
 		for hwmodDesc in self.hwMods:
 			params = hwmodDesc.getParameters()
-			payload.append(self.plModStruct.pack(len(params)))
+			payload.append(self.plModStruct.pack(len(params), 0, 0, 0))
 			payload.append(self.packString(hwmodDesc.getModuleName()))
 			for pName, pVal in dictItems(params):
 				payload.append(self.packString(pName))
@@ -1595,7 +1597,8 @@ def fromBytes(cls, payload):
 			fupSources = []
 			kopSources = []
 			offset = 0
-			nrAwl, nrSym, nrHw, nrLib, nrFup, nrKop = cls.plHdrStruct.unpack_from(
+			nrAwl, nrSym, nrHw, nrLib, nrFup, nrKop,\
+			_, _, _, _, _, _, _, _, _, _ = cls.plHdrStruct.unpack_from(
 								payload, offset)
 			offset += cls.plHdrStruct.size
 			def unpackSrcs(srcClass, sourcesList, count, offset):
@@ -1613,7 +1616,7 @@ def unpackSrcs(srcClass, sourcesList, count, offset):
 			offset = unpackSrcs(AwlSource, awlSources, nrAwl, offset)
 			offset = unpackSrcs(SymTabSource, symTabSources, nrSym, offset)
 			for i in range(nrHw):
-				(nrParam, ) = cls.plModStruct.unpack_from(
+				nrParam, _, _, _ = cls.plModStruct.unpack_from(
 						payload, offset)
 				offset += cls.plModStruct.size
 				modName, count = cls.unpackString(payload, offset)