diff --git a/VM registers.xlsx b/VM registers.xlsx
new file mode 100644
index 0000000..9bf3218
Binary files /dev/null and b/VM registers.xlsx differ
diff --git a/scope.py b/scope.py
index d171c94..8d12787 100644
--- a/scope.py
+++ b/scope.py
@@ -5,9 +5,7 @@ from streams import SerialStream
 
 class Scope(object):
 
-    def __init__(self, stream=None):
-        if stream is None:
-            stream = SerialStream()
+    def __init__(self, stream):
         self._stream = stream
 
     async def reset(self):
@@ -23,7 +21,7 @@ class Scope(object):
 
 
 async def main():
-    s = Scope()
+    s = Scope(SerialStream())
     await s.reset()
     print(await s.get_revision())
 
diff --git a/streams.py b/streams.py
index 9fb4f3a..8f60ec1 100644
--- a/streams.py
+++ b/streams.py
@@ -1,18 +1,29 @@
 
 import asyncio
-import glob
+import os
 import serial
+import serial.tools.list_ports
 
 
-class SerialStream(object):
-    
-    def __init__(self, device=None, loop=None, **kwargs):
-        if device is None:
-            device = (glob.glob('/dev/tty.usb*') + glob.glob('/dev/ttyUSB*'))[0]
-        self._connection = serial.Serial(device, timeout=0, write_timeout=0, **kwargs)
+class SerialStream:
+
+    @staticmethod
+    def available_ports():
+        return [port.device for port in serial.tools.list_ports.comports()]
+
+    def __init__(self, port=-1, loop=None, **kwargs):
+        self._device = self.available_ports()[port]
+        self._connection = serial.Serial(self._device, timeout=0, write_timeout=0, **kwargs)
         self._loop = loop if loop is not None else asyncio.get_event_loop()
         self._input_buffer = b''
 
+    def __repr__(self):
+        return '<{}:{}>'.format(self.__class__.__name__, self._device)
+
+    def close(self):
+        self._connection.close()
+        self._connection = None
+
     async def write(self, data):
         while data:
             n = await self._write(data)
@@ -24,7 +35,9 @@ class SerialStream(object):
         return future
 
     def _feed_data(self, data, future):
-        future.set_result(self._connection.write(data))
+        n = self._connection.write(data)
+        print('<write: {}>'.format(repr(data[:n])))
+        future.set_result(n)
         self._loop.remove_writer(self._connection)
 
     async def read(self, n=None):
@@ -62,7 +75,9 @@ class SerialStream(object):
         return future
 
     def _handle_data(self, n, future):
-        future.set_result(self._connection.read(n if n is not None else self._connection.in_waiting))
+        data = self._connection.read(n if n is not None else self._connection.in_waiting)
+        print('<read: {}>'.format(repr(data)))
+        future.set_result(data)
         self._loop.remove_reader(self._connection)
 
 
diff --git a/vm.py b/vm.py
new file mode 100644
index 0000000..3ecec3b
--- /dev/null
+++ b/vm.py
@@ -0,0 +1,252 @@
+
+
+import asyncio
+import numpy as np
+import struct
+
+
+class VirtualMachine:
+
+    class Transaction:
+        def __init__(self, vm):
+            self._vm = vm
+        def append(self, cmd):
+            self._data += cmd
+        async def __aenter__(self):
+            self._data = b''
+            self._vm._transactions.append(self)
+            return self
+        async def __aexit__(self, exc_type, exc_value, traceback):
+            self._vm._transactions.pop()
+            if exc_type is None:
+                await self._vm.issue(self._data)
+            return False
+
+    Registers = {
+        "vrTriggerLogic": (1, 0x05, '''Trigger Logic, one bit per channel (0 => Low, 1 => High)''', 'uint'),
+        "vrTriggerMask": (1, 0x06, '''Trigger Mask, one bit per channel (0 => Don’t Care, 1 => Active)''', 'uint'),
+        "vrSpockOption": (1, 0x07, '''Spock Option Register (see bit definition table for details)''', 'uint'),
+        "vrSampleAddress": (3, 0x08, '''Sample address (write) 24 bit''', 'uint'),
+        "vrSampleCounter": (3, 0x0b, '''Sample address (read) 24 bit''', 'uint'),
+        "vrTriggerIntro": (2, 0x32, '''Edge trigger intro filter counter (samples/2)''', 'uint'),
+        "vrTriggerOutro": (2, 0x34, '''Edge trigger outro filter counter (samples/2)''', 'uint'),
+        "vrTriggerValue": (2, 0x44, '''Digital (comparator) trigger (signed)''', 'int'),
+        "vrTriggerTime": (4, 0x40, '''Stopwatch trigger time (ticks)''', 'uint'),
+        "vrClockTicks": (2, 0x2e, '''Master Sample (clock) period (ticks)''', 'uint'),
+        "vrClockScale": (2, 0x14, '''Clock divide by N (low byte)''', 'uint'),
+        "vrTraceOption": (1, 0x20, '''Trace Mode Option bits''', 'uint'),
+        "vrTraceMode": (1, 0x21, '''Trace Mode (see Trace Mode Table)''', 'uint'),
+        "vrTraceIntro": (2, 0x26, '''Pre-trigger capture count (samples)''', 'uint'),
+        "vrTraceDelay": (4, 0x22, '''Delay period (uS)''', 'uint'),
+        "vrTraceOutro": (2, 0x2a, '''Post-trigger capture count (samples)''', 'uint'),
+        "vrTimeout": (2, 0x2c, '''Auto trace timeout (auto-ticks)''', 'uint'),
+        "vrPrelude": (2, 0x3a, '''Buffer prefill value''', 'uint'),
+        "vrBufferMode": (1, 0x31, '''Buffer mode''', 'uint'),
+        "vrDumpMode": (1, 0x1e, '''Dump mode''', 'uint'),
+        "vrDumpChan": (1, 0x30, '''Dump (buffer) Channel (0..127,128..254,255)''', 'uint'),
+        "vrDumpSend": (2, 0x18, '''Dump send (samples)''', 'uint'),
+        "vrDumpSkip": (2, 0x1a, '''Dump skip (samples)''', 'uint'),
+        "vrDumpCount": (2, 0x1c, '''Dump size (samples)''', 'uint'),
+        "vrDumpRepeat": (2, 0x16, '''Dump repeat (iterations)''', 'uint'),
+        "vrStreamIdent": (1, 0x36, '''Stream data token''', 'uint'),
+        "vrStampIdent": (1, 0x3c, '''Timestamp token''', 'uint'),
+        "vrAnalogEnable": (1, 0x37, '''Analog channel enable (bitmap)''', 'uint'),
+        "vrDigitalEnable": (1, 0x38, '''Digital channel enable (bitmap)''', 'uint'),
+        "vrSnoopEnable": (1, 0x39, '''Frequency (snoop) channel enable (bitmap)''', 'uint'),
+        "vpCmd": (1, 0x46, '''Command Vector''', 'uint'),
+        "vpMode": (1, 0x47, '''Operation Mode (per command)''', 'uint'),
+        "vpOption": (2, 0x48, '''Command Option (bits fields per command)''', 'uint'),
+        "vpSize": (2, 0x4a, '''Operation (unit/block) size''', 'uint'),
+        "vpIndex": (2, 0x4c, '''Operation index (eg, P Memory Page)''', 'uint'),
+        "vpAddress": (2, 0x4e, '''General purpose address''', 'uint'),
+        "vpClock": (2, 0x50, '''Sample (clock) period (ticks)''', 'uint'),
+        "vpModulo": (2, 0x52, '''Modulo Size (generic)''', 'uint'),
+        "vpLevel": (2, 0x54, '''Output (analog) attenuation (unsigned)''', 'uint'),
+        "vpOffset": (2, 0x56, '''Output (analog) offset (signed)''', 'int'),
+        "vpMask": (2, 0x58, '''Translate source modulo mask''', 'uint'),
+        "vpRatio": (4, 0x5a, '''Translate command ratio (phase step)''', 'uint'),
+        "vpMark": (2, 0x5e, '''Mark count/phase (ticks/step)''', 'uint'),
+        "vpSpace": (2, 0x60, '''Space count/phase (ticks/step)''', 'uint'),
+        "vpRise": (2, 0x82, '''Rising edge clock (channel 1) phase (ticks)''', 'uint'),
+        "vpFall": (2, 0x84, '''Falling edge clock (channel 1) phase (ticks)''', 'uint'),
+        "vpControl": (1, 0x86, '''Clock Control Register (channel 1)''', 'uint'),
+        "vpRise2": (2, 0x88, '''Rising edge clock (channel 2) phase (ticks)''', 'uint'),
+        "vpFall2": (2, 0x8a, '''Falling edge clock (channel 2) phase (ticks)''', 'uint'),
+        "vpControl2": (1, 0x8c, '''Clock Control Register (channel 2)''', 'uint'),
+        "vpRise3": (2, 0x8e, '''Rising edge clock (channel 3) phase (ticks)''', 'uint'),
+        "vpFall3": (2, 0x90, '''Falling edge clock (channel 3) phase (ticks)''', 'uint'),
+        "vpControl3": (1, 0x92, '''Clock Control Register (channel 3)''', 'uint'),
+        "vrEepromData": (1, 0x10, '''EE Data Register''', 'uint'),
+        "vrEepromAddress": (1, 0x11, '''EE Address Register''', 'uint'),
+        "vrConverterLo": (2, 0x64, '''VRB ADC Range Bottom (D Trace Mode)''', 'uint'),
+        "vrConverterHi": (2, 0x66, '''VRB ADC Range Top (D Trace Mode)''', 'uint'),
+        "vrTriggerLevel": (2, 0x68, '''Trigger Level (comparator, unsigned)''', 'uint'),
+        "vrLogicControl": (1, 0x74, '''Logic Control''', 'uint'),
+        "vrRest": (2, 0x78, '''DAC (rest) level''', 'uint'),
+        "vrKitchenSinkA": (1, 0x7b, '''Kitchen Sink Register A''', 'uint'),
+        "vrKitchenSinkB": (1, 0x7c, '''Kitchen Sink Register B''', 'uint'),
+    }
+
+    def __init__(self, stream):
+        self._stream = stream
+        self._transactions = []
+
+    def new_transaction(self):
+        return self.Transaction(self)
+
+    async def issue(self, cmd):
+        if isinstance(cmd, str):
+            cmd = cmd.encode('ascii')
+        if not self._transactions:
+            await self._stream.write(cmd)
+            await self._stream.readuntil(cmd)
+        else:
+            self._transactions[-1].append(cmd)
+
+    async def read_reply(self):
+        return (await self.read_replies(1))[0]
+
+    async def read_replies(self, n):
+        await self._stream.readuntil(b'\r')
+        replies = []
+        for i in range(n):
+            replies.append((await self._stream.readuntil(b'\r'))[:-1])
+        return replies
+
+    async def reset(self):
+        await self._stream.write(b'!')
+        await self._stream.readuntil(b'!')
+
+    async def set_register(self, name, value):
+        width, base, desc, dtype = self.Registers[name]
+        bs = struct.pack('<i' if dtype == 'int' else '<I', value)
+        cmd = '{:02x}@'.format(base) + 'z'.join('{:02x}'.format(bs[i]) for i in range(width)) + 's'
+        await self.issue(cmd)
+
+    async def set_registers(self, **kwargs):
+        async with self.new_transaction():
+            for name, value in kwargs.items():
+                await self.set_register(name, value)
+
+    async def get_register(self, name):
+        width, base, desc, dtype = self.Registers[name]
+        await self.issue('{:02x}@p'.format(base))
+        bs = []
+        for i in range(width):
+            bs.append(int(await self.read_reply(), 16))
+            if i < width-1:
+                await self.issue(b'np')
+        for i in range(4 - width):
+            bs.append(0)
+        value = struct.unpack('<i' if dtype == 'int' else '<I', bytes(bs))[0]
+        return value
+
+    async def get_revision(self):
+        await self.issue(b'?')
+        return await self.read_reply()
+
+    async def capture_spock_registers(self):
+        await self.issue(b'<')
+
+    async def program_spock_registers(self):
+        await self.issue(b'>')
+
+    async def configure_device_hardware(self):
+        await self.issue(b'U')
+
+    async def streaming_trace(self):
+        await self.issue(b'T')
+
+    async def triggered_trace(self):
+        await self.issue(b'D')
+
+    async def cancel_trace(self):
+        await self.issue(b'K')
+
+    async def sample_dump_csv(self):
+        await self.issue(b'S')
+
+    async def analog_dump_binary(self):
+        await self.issue(b'S')
+
+    async def read_wavetable(self, size=1024, address=0):
+        async with self.new_transaction():
+            await self.set_registers(vpSize=size, vpAddress=address)
+            await self.issue(b'R')
+        return await self._stream.readexactly(size)
+
+    async def write_wavetable(self, data, address=0):
+        async with self.new_transaction():
+            await self.set_registers(vpSize=1, vpAddress=address)
+            for byte in data:
+                await self.issue('{:02x}W'.format(byte))
+
+    async def synthesize_wavetable(self, mode='sine', ratio=0.5):
+        mode = {'sine': 0, 'sawtooth': 1, 'exponential': 2, 'square': 3}[mode.lower()]
+        async with self.new_transaction():
+            await self.set_registers(vpCmd=0, vpMode=mode, vpRatio=int(max(0, min(ratio, 1))*65535))
+            await self.issue(b'Y')
+
+    async def translate_wavetable(self, ratio, level=1, offset=0, size=0, index=0, address=0):
+        async with self.new_transaction():
+            await self.set_registers(vpCmd=0, vpMode=0, vpLevel=int(65535*level), vpOffset=int(65535*offset), vpRatio=ratio,
+                                     vpSize=size, vpIndex=index, vpAddress=address)
+            await self.issue(b'X')
+
+    async def stop_waveform_generator(self):
+        async with self.new_transaction():
+            await self.set_registers(vpCmd=1, vpMode=0)
+            await self.issue(b'Z')
+
+    async def start_waveform_generator(self, clock, modulo, mark, space, rest, option):
+        async with self.new_transaction():
+            await self.set_registers(vpCmd=2, vpMode=0, vpClock=clock, vpModulo=modulo, 
+                                     vpMark=mark, vpSpace=space, vrRest=rest, vpOption=option)
+            await self.issue(b'Z')
+
+    async def start_clock_generator(self):
+        async with self.new_transaction():
+            await self.set_registers(vpCmd=3, vpMode=0)
+            await self.issue(b'Z')
+
+    async def read_eeprom(self, address):
+        async with self.new_transaction():
+            await self.set_registers(vrEepromAddress=address)
+            await self.issue(b'r')
+        return int(await self.read_reply(), 16)
+
+    async def write_eeprom(self, address, data):
+        async with self.new_transaction():
+            await self.set_registers(vrEepromAddress=address, vrEepromData=data)
+            await self.issue(b'w')
+        return int(await self.read_reply(), 16)
+
+
+async def main():
+    from streams import SerialStream
+    vm = VirtualMachine(SerialStream())
+    await vm.reset()
+    print(await vm.get_revision())
+    print(await vm.get_register('vrConverterLo'))
+    print(await vm.get_register('vrTriggerLevel'))
+    print(await vm.get_register('vrConverterHi'))
+    await vm.set_register('vrTriggerLevel', 15000)
+    print(await vm.get_register('vrTriggerLevel'))
+    n = await vm.read_eeprom(0)
+    print(n)
+    print(await vm.write_eeprom(0, n+1))
+    print(await vm.read_eeprom(0))
+    async with vm.new_transaction():
+        await vm.set_registers(vrKitchenSinkB=0x40)
+        await vm.configure_device_hardware()
+    await vm.synthesize_wavetable('sawtooth')
+    #data = await vm.read_wavetable()
+    #global array
+    #array = np.ndarray(buffer=data, shape=(len(data),), dtype='uint8')
+    #print(array)
+    await vm.translate_wavetable(671088)
+    await vm.start_waveform_generator(clock=40, modulo=1000, mark=10, space=1, rest=0x7f00, option=0x8004)
+
+if __name__ == '__main__':
+    asyncio.get_event_loop().run_until_complete(main())
+