Using Python 3 to Build a Cloud Computing Service for

my Superboard II

David Beazley(http://www.dabeaz.com)

Presented at PyCon 2011Atlanta

http://pycon.blip.tv/file/4878868/

Note: This talk involves a number of live demonstrations. You will probably enjoy

it more by watching the PyCon 2011 video presentation

(Drumroll...)

It Begins

Byte Magazine, January, 1979

Personal History

• Superboard II was my family's first computer

• What I first learned to program (~1979)

• It had everything that a kid could want

Easy Setup!

Peripherals!

Potentially Lethal Suggestions!

Schematics!

You could get an electric

shockYou could

look inside!

Pure Awesome!You could program

Pure Awesome!You could hack!

Note the encouragement

Backstory

• 1982-2010. Superboard sits in mom's basement

• July 2010. Eric Floehr mentions SB at Scipy

• August 2010. Brother brings SB to Chicago

• It still works! (to my amazement)

Question• What do you do with an old Superboard II

• 1 Mhz 6502 CPU

• 8K RAM

• 8K Microsoft Basic (vers. 1.0)

• 300 Baud Cassette Audio Interface

• 1K Video Ram (24x24 visible characters)

• Not a modern powerhouse

TO THE CLOUD!

HOW?(with Python 3 awesomeness of course)

(plus some ØMQ and Redis)

(and some 6502 assembler)

Getting to the CloudThis is the only I/O

A pair of RCA audio jacks

Used for cassette tape storage

Not too promising

A Possible Solution

Cassette Interface

• Behind the RCA jacks, sits a real serial "port"

• Motorola 6850 ACIA

• Ports are a 300 baud audio stream encoded via Kansas City Standard

• Might be able to hack it

Byte, Feb. 1976

Python Audio Processing

• pyaudio

• http://http://people.csail.mit.edu/hubert/pyaudio/

• A Python interface to the portaudio C library

• Allows real-time access to audio line in/out

• I ported it to Python 3

Reading Audio Inputimport pyaudiop = pyaudio.PyAudio()stream = p.open(format=pyaudio.paInt8, channels=1, rate=9600, chunksize=1024, input=True)while True: sample = stream.read(1024) process_sample(sample)

Building a Python Modem

pyaudiowriter

pyaudioreader

byte encoder

byte decoder

TCP socket

client

reader thread

writer thread

• A network socket bridged to two real-time audio encoding/decoding threads

KCS Audio Encoding

0 = 1 =

(4 cycles @ 1200 Hz) (8 cycles @ 2400 Hz)

'A' = 0x41 (01000001)

0 0 0 0 0 0 1 1110

start data stop

KCS Audio Decoding

89, 103, 117, 151, 194, 141, 99, 64, 89, 112, 141, 203, 152, 107, 88, ...

samples (8-bit)

000111000111000111000111000111111000000111111000000111111000000111111...

sign bits (0 = neg, 1= pos)

0001001001001001001001001001000001000001000001000001000001000001000001...

Idea: Each 1 bit represents a 0-crossing

sign changes (XOR adjacent bits)

Example Code

def generate_sign_change_bits(stream): previous = 0 while True: samples = stream.read(CHUNKSIZE)

# Emit a stream of sign-change bits for byte in samples: signbit = byte & 0x80 yield 1 if (signbit^previous) else 0 previous = signbit

KCS Bit Decoding

1001001001001001001001001001

idle (constant 1)

data bytestart stop

1 1 10 0 0 0 0

1001001001001001 discard

Sample buffer (size = audio samples for 1 bit)

Sign Change Bits push

~ 8 sign changes ~ 16 sign changes

0 1

Example Codefrom collections import deque

# Sample buffersample = deque(maxlen=SAMPLES_PER_BIT)

for b in generate_sign_change_bits(stream): sample.append(b) nchanges = sum(sample) if nchanges < 10: # Detected a start bit # Sample next 8 data bits ...

(The actual code is more optimized)

DemoMy Mac (linked via audio)

Interlude• It's Alive!

• Basic communication is just the start!

This is uploading machine code

~500 lines of 6502 assembler...getvar_copy_string:! ;; Move the variable address to INDIRECT where we can use it! LDA![0x95, Y]! ; Length! STA!%MEM_LENGTH! INY! LDA![0x95, Y]! ; address (low)! STA!%INDIRECT! INY! LDA![0x95, Y]! ; address (high)! STA!%INDIRECT+1! LDY!#0x00...

Wrote a 6502 assembler

~500 lines of Python 3

This is uploading machine code

~500 lines of 6502 assembler...getvar_copy_string:! ;; Move the variable address to INDIRECT where we can use it! LDA![0x95, Y]! ; Length! STA!%MEM_LENGTH! INY! LDA![0x95, Y]! ; address (low)! STA!%INDIRECT! INY! LDA![0x95, Y]! ; address (high)! STA!%INDIRECT+1! LDY!#0x00...

Wrote a 6502 assembler

~500 lines of Python 3

Under the covers

msgdrv.asm

asm6502.py

msgdrv.hex

.1C00/2005AEEE1E1EAD1E1E8D

pymodem

This is uploading machine code

~500 lines of 6502 assembler...getvar_copy_string:! ;; Move the variable address to INDIRECT where we can use it! LDA![0x95, Y]! ; Length! STA!%MEM_LENGTH! INY! LDA![0x95, Y]! ; address (low)! STA!%INDIRECT! INY! LDA![0x95, Y]! ; address (high)! STA!%INDIRECT+1! LDY!#0x00...

Wrote a 6502 assembler

~500 lines of Python 3

Under the covers

msgdrv.asm

asm6502.py

msgdrv.hex

.1C00/2005AEEE1E1EAD1E1E8D

pymodem

Messaging Driver

Superboard II Client

request

control

• Superboard issues requests

• Client responds and gets control

• Driver coexists with BASIC

message driver

BASIC Workspace7168 bytes

1024 bytes

This is uploading machine code

~500 lines of 6502 assembler...getvar_copy_string:! ;; Move the variable address to INDIRECT where we can use it! LDA![0x95, Y]! ; Length! STA!%MEM_LENGTH! INY! LDA![0x95, Y]! ; address (low)! STA!%INDIRECT! INY! LDA![0x95, Y]! ; address (high)! STA!%INDIRECT+1! LDY!#0x00...

Wrote a 6502 assembler

~500 lines of Python 3

Under the covers

msgdrv.asm

asm6502.py

msgdrv.hex

.1C00/2005AEEE1E1EAD1E1E8D

pymodem

Messaging Driver

Superboard II Client

request

control

• Superboard issues requests

• Client responds and gets control

• Driver coexists with BASIC

message driver

BASIC Workspace7168 bytes

1024 bytes

Example of making a request

10 A = 9620 B = 4230 C$ = "FOO"40 S = USR(37)

Client controlPEEK - Get a memory regionPOKE - Set a memory regionGET - Get a BASIC variableSET - Set a BASIC variableRETURN - Return to BASIC

Distributed shared memory!

Messaging Architecture• There are two parts (driver and a client)

superboardmessagedriver

BASIC

message client

Python 3

pymodemsocketaudio

• Uses a binary message protocol

USR(37) : \x20 \x06 \x01 \x25 \x00 \x02

Command Size Seq LRCData

• Protocol details not so interesting

Message Driver

• Interacts directly with Microsoft BASIC

• Uses "Undocumented" ROM routines

• Accesses BASIC interpreter memory

• For this, some resources online

• http://osiweb.org

Client Architecture• Client bridges Superboard II to the outside world

• Uses ØMQ (http://www.zeromq.com)

• And pyzmq (http://github.com/zeromq/pyzmq)

Message client

Python 3

pymodemsocketaudio

ØMQ

Services

Request Publishing• Requests are broadcast on a ØMQ PUB socket

• Retransmitted every few seconds if no response

Message client

Python 3

ØMQ PUBUSR(37) "37 1" "37 1" "37 1"To the

"Cloud"

• Requests include the USR code and a sequence #

...

Service Subscription• Services simply subscribe to the request feed

import zmqcontext = zmq.Context()requests = context.socket(zmq.SUB)requests.connect("tcp://msgclient:21001")requests.setsockopt(zmq.SUBSCRIBE,b"37 ")

• Now wait for the requests to arrivewhile True: request = requests.recv()

• Clients are separate programs--live anywhere

Request Response• Message client has a separate ØMQ REP socket

• Used by services to respond

Message client

Python 3

ØMQ PUBUSR(37) "37 1"

• Service initially acks by echoing request back

• On success, can issue more commands

ØMQ REP Service (subscribed to 37)commands

driver

Command Connection• Setting up the command socket

commands = context.socket(zmq.REQ)commands.connect("tcp://msgclient:21002")

• Complete request/response cycle

while True: request = requests.recv() commands.send(request) # Echo back resp = commands.recv() if resp[:2] == b'OK': # In control of Superboard # Do evil stuff ...

Commands• Commands are just simple byte strings

b"RETURN VALUE"b"PEEK ADDR SIZE"b"POKE ADDR DATA"b"GET VARNAME"b"SET VARNAME VALUE"

• Response codesb"OK DATA"b"FAIL MSG"b"IGNORE"b"BUSY"

Interactive Demo>>> request_sock.recv()b'37 1'>>> command_sock.send(b'37 1')>>> command_sock.recv()b'OK'>>> command_sock.send(b'GET A')>>> command_sock.recv()b'OK 96.0'>>> command_sock.send(b'GET B')>>> command_sock.recv()b'OK 42.0'>>> command_sock.send(b'SET Q 2')>>> command_sock.recv()b'OK'>>> command_sock.send(b'SET R 12')>>> command_sock.recv()b'OK'>>> command_sock.send(b'RET 0')>>> command_sock.recv()b'OK'>>>

Big PictureMessage client

ØMQ PUB

ØMQ REPUSR(N)

Up to 65536 Service IDs (N)

• Services can live anywhere

• Written in any language

• No real limit except those imposed by ØMQ

Big Iron

Superboard Emulation• I dumped the BASIC and system ROMS

• Loaded them into Py65

• Py65 : A 6502 Emulator Written in Python

https://github.com/mnaberez/py65

• Work of Mike Naberezny

• I ported it to Python 3

Emulation in 60 SecondsYou start with the

Superboard II memory map (provided)

Emulation in 60 Seconds

You identify hardware devices

Emulation in 60 SecondsYou read

(about keyboards)

Emulation in 60 SecondsYou read

(about video ram)

Emulation in 60 SecondsYou read

(about ACIA chips)

Emulation in 60 SecondsThen you just plug it into py65 (sic)def map_hardware(self,m): # Video RAM at 0xd000-xd400 m.subscribe_to_write(range(0xd000,0xd400), self.video_output)

# Monitor the polled keyboard port m.subscribe_to_read([0xdf00], self.keyboard_read) m.subscribe_to_write([0xdf00], self.keyboard_write)

# ACIA Interface m.subscribe_to_read([0xf000], self.acia_status) m.subscribe_to_read([0xf001], self.acia_read) m.subscribe_to_write([0xf001], self.acia_write)

# Bad memory address to force end to memory check m.subscribe_to_read([0x2000], lambda x: 0)

Interactive Demo

Question

• What do you do with an emulated Superboard?

A Superboard Cloud

StoredInstances(images of running

machines)

Program Storage

10 PRINT "I WILL THINK OF A"15 PRINT "NUMBER BETWEEN 1 AND 100"20 PRINT "TRY TO GUESS WHAT IT IS"25 N = 030 X = INT(RND(56)*99+1)35 PRINT40 PRINT "WHATS YOUR GUESS ";50 INPUT G

10 PRINT "HELLO WORLD"20 END

10 FOR I = 1 TO 100020 PRINT I30 NEXT I20 END

DatastoreCloudService

VirtualizedSuperboard CPUs

Building The Cloud

• I built it using Redis (http://redis.io)

• Ported py-redis to Python 3

• Redis is cool

• Can use it as a key-value store

• Has other data structures (sets, hashes, etc.)

• Queuing

• Atomic operations

Redis Example

import redisdb = redis.Redis()

# Key-value storedb.set('foo',data)data = db.get('foo')

# Queuingdb.lpush('queue',work)work = db.brpop('queue')

Superboard Cloud Features

• Remote program store

• Load/save programs

• Instance creation

• Creation

• Run with input

• Distributed shared memory

• It must be usable from the Superboard II

Program Load/Store

• BASIC program & workspace memory directly manipulated by the message driver

• Stored in Python object and pickled to Redis

settings

program

stringsBASIC

redis

msgdriver

cloudservice get

set

Instances

• Instances are a running Superboard

• 8K Program Memory

• 1K Video RAM

• Stored CPU context (registers, etc.)

• Stored in a Python object

• Pickled to Redis when inactive

Instance Execution• "Runner" programs watch a Redis queue

import redisr = redis.Redis()...while True: work = r.brpop("queue") # Wait for work ... inst = load_instance() # Get instance run_emulation(work) # Run emulation save_instance(inst) # Save instance

• Based on supplying keyboard input to SB

• Instance runs until no more input available

Instance Concurrency

• Can have arbitrary number of runners

Runners

Redis

• Asynchronous execution (w/ Superboard)

• Uses Redis setnx() for locking

import superboard as skynet

ØMQ PUB

ØMQ REP

Up to 65536 Service IDs (N)

Big Iron

pymodem

CloudService

StoredInstances

VirtualizedSuperboard CPUs

10 PRINT "I WILL THINK OF A"15 PRINT "NUMBER BETWEEN 1 AND 100"20 PRINT "TRY TO GUESS WHAT IT IS"25 N = 030 X = INT(RND(56)*99+1)35 PRINT40 PRINT "WHATS YOUR GUESS ";50 INPUT G

10 PRINT "HELLO WORLD"20 END

10 FOR I = 1 TO 100020 PRINT I30 NEXT I20 END

programs

redis

WHY?!

Non-Answer

• I don't actually want to use my Superboard II

• It's awful!

• It was painful even in 1980

A Better Answer• For fun

• Also to create a glorious mess!

• Everything a systems hacker could want!

• Hardware, device drivers, signal processing, protocols, networks, message passing, threads, synchronization, debugging, software design, testing, deployment, etc.

• Awesome!

Real Answer : Python 3

• Can Python 3 be used for anything real?

• I needed to check it out myself

• On a non-trivial project with many moving parts

• And with a variety of library dependencies

Lessons Learned

• You can use Python 3 to do real work

• However, it’s bleeding edge

• You really have to know what you’re doing

• Especially with respect to bytes/unicode

• Must be prepared to port and/or patch

Porting Experience

• py65 (easy, some bytes issues)

• pyredis (easy, bytes/unicode issues)

• pypng (hard, really messy I/O)

• pyaudio (hard, C extensions)

• pyzmq (worked, Cython patch for Py3.2)

Finding Python 3 Code

• Every single package I used was downloaded from development repositories (github, subversion, etc, etc)

• You can often find Python 3 compatible libraries in project forks or issue trackers if you look for it

My Thoughts

• Python 3 is cool

• It keeps getting better

>>> import numpy>>>

• It’s different and fun

• It might be a great language for distributed computing, messaging, and other applications

That’s All Folks!• Thanks for listening!

• Look for the “Python Cookbook, 3rd” edition in late 2011!

• More info on my blog

• http://www.dabeaz.com