diff --git a/artiq/devices/corecom_serial.py b/artiq/devices/corecom_serial.py
index f17a94672..9d3712c34 100644
--- a/artiq/devices/corecom_serial.py
+++ b/artiq/devices/corecom_serial.py
@@ -1,6 +1,23 @@
-import os
-import struct
-import termios
+import os, termios, struct
+from enum import Enum
+
+class _MsgType(Enum):
+	KERNEL_FINISHED		= 0x01
+	RPC_REQUEST			= 0x02
+
+def _write_exactly(f, data):
+	remaining = len(data)
+	pos = 0
+	while remaining:
+		written = f.write(data[pos:])
+		remaining -= written
+		pos += written
+
+def _read_exactly(f, n):
+	r = bytes()
+	while(len(r) < n):
+		r += f.read(n - len(r))
+	return r
 
 class CoreCom:
 	def __init__(self, dev="/dev/ttyUSB1", baud=115200):
@@ -31,5 +48,43 @@ class CoreCom:
 		self.close()
 
 	def run(self, kcode):
-		self.port.write(struct.pack(">LL", 0x5a5a5a5a, len(kcode)))
-		self.port.write(kcode)
+		_write_exactly(self.port, struct.pack(">ll", 0x5a5a5a5a, len(kcode)))
+		_write_exactly(self.port, kcode)
+		# FIXME: when loading immediately after a board reset, we erroneously get some zeros back.
+		# Ignore them with a warning for now.
+		spurious_zero_count = 0
+		while True:
+			(reply, ) = struct.unpack("b", _read_exactly(self.port, 1))
+			if reply == 0:
+				spurious_zero_count += 1
+			elif reply == 0x4f:
+				break
+			else:
+				raise IOError("Incorrect reply from device: "+hex(reply))
+		if spurious_zero_count:
+			print("Warning: received {} spurious zeros".format(spurious_zero_count))
+
+	def _wait_sync(self):
+		recognized = 0
+		while recognized < 4:
+			(c, ) = struct.unpack("b", _read_exactly(self.port, 1))
+			if c == 0x5a:
+				recognized += 1
+			else:
+				recognized = 0
+
+	def serve(self, rpc_map):
+		while True:
+			self._wait_sync()
+			msg = _MsgType(*struct.unpack("b", _read_exactly(self.port, 1)))
+			if msg == _MsgType.KERNEL_FINISHED:
+				return
+			elif msg == _MsgType.RPC_REQUEST:
+				rpc_num, n_args = struct.unpack(">hb", _read_exactly(self.port, 3))
+				args = []
+				for i in range(n_args):
+					args.append(*struct.unpack(">l", _read_exactly(self.port, 4)))
+				r = rpc_map[rpc_num](*args)
+				if r is None:
+					r = 0
+				_write_exactly(self.port, struct.pack(">l", r))