diff --git a/stm32loader/emulated/fake.py b/stm32loader/emulated/fake.py
index e69de29..4a49c6b 100644
--- a/stm32loader/emulated/fake.py
+++ b/stm32loader/emulated/fake.py
@@ -0,0 +1,136 @@
+import struct
+
+from stm32loader.bootloader import Stm32Bootloader
+
+
+class FakeConnection:
+
+    ACK = Stm32Bootloader.Reply.ACK.value
+    Command = Stm32Bootloader.Command
+
+    COMMAND_RESPONSES = {
+        # Return length, bootloader version, commands
+        # Version 5, 0x0=GET 0x01=GET_VERSION 0x02=GET_ID 0x11=READ_MEMORY 0x31=WRITE_MEMORY
+        # 0x43=ERASE 0x44=EXTENDED_ERASE
+        Command.GET: [7, 0x05, [0x0, 0x01, 0x02, 0x11, 0x31, 0x43, 0x44], ACK],
+        # Product ID: 0x422
+        Command.GET_ID: [1, [0x04, 0x22]],
+    }
+
+    READ_RESPONSES = {
+        # Read flash size, F1.
+        (0x_1FFF_F7E0, 2): [[0x00, 0x01]],
+
+        # Read flash size, F3.
+        (0x_1FFF_F7CC, 2): [[0x00, 0x01]],
+
+        # Read device UID, F1.
+        (0x_1FFF_F7E8, 12):  [[1, 0, 3, 2, 7, 6, 5, 4, 0xB, 0xA, 9, 8]],
+
+        # Read device UID, F3.
+        (0x_1FFF_F7AC, 12): [[1, 0, 3, 2, 7, 6, 5, 4, 0xB, 0xA, 9, 8]],
+
+        # Read Bootloader ID.
+        (0x_1FFF_F796, 1): [0x41],
+    }
+
+    def __init__(self):
+        self.next_return = []
+        self.timeout = 2
+        self.receiver = self.receive()
+
+        self.flash_offset = 0x_0800_0000
+        self.flash_size = 2 * 1024 * 1024
+        self.flash_memory = bytearray(2 * 1024 * 1024)
+
+        # Start coroutine.
+        next(self.receiver)
+
+    def ack(self):
+        self.next_return.append(self.ACK)
+
+    def receive(self):
+        while True:
+            # Receive a command coming in.
+            command_bytes = yield
+            command_value = struct.unpack("B", command_bytes)[0]
+
+            # Receive CRC byte.
+            yield
+            self.ack()
+
+            if command_value in self.COMMAND_RESPONSES:
+                self.next_return.extend(self.COMMAND_RESPONSES[command_value])
+            elif command_value == self.Command.READ_MEMORY.value:
+                # Receive address with CRC.
+                address_bytes = yield
+                address = struct.unpack(">I", address_bytes[0:4])[0]
+                self.ack()
+
+                # Receive number of bytes
+                length_bytes = yield
+                length = struct.unpack("B", length_bytes)[0] + 1
+
+                # Receive CRC
+                yield
+                self.ack()
+
+                # Set up data to respond.
+                if self.flash_offset <= address < self.flash_offset + self.flash_size:
+                    # Return flash data.
+                    flash_offset = address - self.flash_offset
+                    self.next_return.append(list(self.flash_memory[flash_offset: flash_offset + length]))
+                else:
+                    self.next_return.extend(self.READ_RESPONSES[(address, length)])
+            elif command_value == self.Command.EXTENDED_ERASE.value:
+                pages_bytes = yield
+                pages = struct.unpack(">H", pages_bytes[0:2])
+                if pages == 0xFFFF:
+                    # Erase all.
+                    self.flash_memory[:] = 0xFF
+                    self.next_return.append(self.ACK)
+            elif command_value == self.Command.WRITE_MEMORY.value:
+                address_bytes = yield
+                address = struct.unpack(">I", address_bytes[0:4])[0]
+                size_bytes = yield
+                byte_count = struct.unpack("B", size_bytes)[0] + 1
+                data = yield
+                crc = yield
+
+                assert len(data) == byte_count, f"Length does not match byte count: {len(data)} vs {byte_count}"
+
+                # Record data in flash memory.
+                flash_offset = address - 0x_0800_0000
+                self.flash_memory[flash_offset: flash_offset + byte_count] = data
+            else:
+                raise NotImplementedError()
+
+    def write(self, data):
+        # Send to coroutine.
+        self.receiver.send(data)
+
+    def read(self, length=1):
+        if self.next_return:
+            value = self.next_return.pop(0)
+            if isinstance(value, int):
+                return [value]
+            return value
+
+        return [self.ACK]
+
+
+class FakeConfiguration:
+
+    def __init__(self, erase, write, verify, firmware_file, family=None):
+        self.erase = erase
+        self.write = write
+        self.verify = verify
+        self.data_file = firmware_file
+        self.unprotect = False
+        self.protect = False
+        self.length = None
+        self.verbosity = 5
+        self.address = 0x_0800_0000
+        self.go_address = None
+        self.family = family
+