diff --git a/migen/sim/__init__.py b/migen/sim/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/migen/sim/ipc.py b/migen/sim/ipc.py
new file mode 100644
index 000000000..ad89ce111
--- /dev/null
+++ b/migen/sim/ipc.py
@@ -0,0 +1,127 @@
+import socket
+import os
+
+#
+# Message classes
+#
+
+class Message:
+	def __init__(self, *pvalues):
+		for parameter, value in zip(self.parameters, pvalues):
+			assert(isinstance(value, parameter[0]))
+			setattr(self, parameter[1], value)
+
+class MessageTick(Message):
+	code = 0
+	parameters = []
+
+class MessageGo(Message):
+	code = 1
+	parameters = []
+
+class MessageWrite(Message):
+	code = 2
+	parameters = [(str, "signal"), (int, "value")]
+
+class MessageRead(Message):
+	code = 3
+	parameters = [(str, "signal")]
+
+class MessageReadReply(Message):
+	code = 4
+	parameters = [(int, "value")]
+
+message_classes = [MessageTick, MessageGo, MessageWrite, MessageRead, MessageReadReply]
+
+#
+# Packing
+#
+
+def _pack_int(v):
+	# TODO
+	return []
+
+def _pack_str(v):
+	# TODO
+	return []
+
+def _pack(message):
+	r = [message.code]
+	for p, t in message.parameters:
+		value = getattr(message, p)
+		assert(isinstance(value, t))
+		if t == int:
+			r += _pack_int(value)
+		elif t == str:
+			r += _pack_str(value)
+		else:
+			raise TypeError
+	return bytes(r)
+
+#
+# Unpacking
+#
+
+def _unpack_int(i):
+	# TODO
+	return 0
+
+def _unpack_str(i):
+	# TODO
+	return ""
+
+def _unpack(message):
+	i = iter(message)
+	code = next(i)
+	msgclass = next(filter(lambda x: x.code == code, message_classes))
+	pvalues = []
+	for p, t in msgclass.parameters:
+		if t == int:
+			v = _unpack_int(i)
+		elif t == str:
+			v = _unpack_str(i)
+		else:
+			raise TypeError
+		pvalues.append(v)
+	return msgclass(*pvalues)
+
+#
+# I/O
+#
+
+class PacketTooLarge(Exception):
+	pass
+	
+class Initiator:
+	def __init__(self, sockaddr="simsocket"):
+		self.sockaddr = sockaddr
+		self.socket = socket.socket(socket.AF_UNIX, socket.SOCK_SEQPACKET)
+		self._cleanup_file()
+		self.socket.bind(self.sockaddr)
+		self.socket.listen(1)
+	
+	def _cleanup_file(self):
+		try:
+			os.remove(self.sockaddr)
+		except OSError:
+			pass
+	
+	def accept(self):
+		self.conn, addr = self.socket.accept()
+	
+	def send(self, message):
+		self.conn.send(_pack(message))
+	
+	def recv(self):
+		maxlen = 4096
+		packet = self.conn.recv(maxlen)
+		if len(packet) >= maxlen:
+			raise PacketTooLarge
+		return _unpack(packet)
+
+	def __del__(self):
+		if hasattr(self, "conn"):
+			self.conn.close()
+		if hasattr(self, "socket"):
+			self.socket.close()
+		self._cleanup_file()