Python on a chip

Python on a Chip
PyMite, a Python Virtual Machine

Jeremy Stott
jeremy@stott.co.nz

Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

Microcontrollers

• Programming Microcontrollers is
fun!

• You can build your own toys / evil
robots

• Even getting lights to blink is fun

• Usually programmed in C,
sometimes C++

http://lighttrees.com/wordpress/archives/category/sculpture

What's wrong with C?!
#include <stdio.h>
int l;int main(int o,char **O,
• Nothing is wrong with C int I){char c,*D=O[1];if(o>0){
for(l=0;D[l ];D[l
++]-=10){D [l++]-=120;D[l]-=
• It's up to the programmer to write good 110;while (!main(0,O,l))D[l]
+= 20; putchar((D[l]+1032)
code /20 ) ;}putchar(10);}else{
c=o+ (D[I]+82)%10-(I>l/2)*
(D[I-l+I]+72)/10-9;D[I]+=I<0?0
• Programmers may suffer from object :!(o=main(c/10,O,I-1))*((c+999
)%10-(D[I]+92)%10);}return o;}
oriented withdrawal syndrome

• Prolonged use of C may cause
inappropriate outbursts of semi-colons;

• You can't do [Python reference] in C

http://www0.us.ioccc.org/years.html#2001

Introducing: Python-On-A-Chip

●
http://code.google.com/p/python-on-a-chip/
●
A project developing PyMite, a Python Virtual Machine
designed to run on Microcontrollers
●
A small growing group > 256 mailing list members
●
Uses 55KB of ROM and 5KB of RAM for "Hello World!"
●
License:
●
Tools: GNU LGPL v2.1 (Lesser GPL)
●
Virtual Machine: GPL v2 (Non Commercial)


Features
It Does:

• Support integers, floats, lists, dicts, functions, modules,
classes, generators, decorators and closures

• Support 25 out of 29 keywords and 89 out of 112 byte codes
from Python 2.6

• Stackless green threads

It Doesn't:

• Have a built in compiler

• Support any of Python's standard libraries

25 out of 29 Keywords?

PyMite supports the following set of Python's keywords
    and      assert    break     class     continue
    def      del       elif      else      for
    from     global    if        import    in
    is       lambda    not       or        pass
    print    raise     return    while     yield

PyMite does not support these keywords
    except exec   finally   try

However, they are working on Exceptions


No Standard Libraries?

Instead of supporting Python's libraries, PyMite offer its own set
of modules. Some of which have the same name as their
Python counterparts.

PyMite Modules
    dict   func   list   string   sys
As well as many built in functions
    abs(x), bytearray(seq), bytearray(len), chr(i),
    eval(co), globals(), id(o), len(obj), locals(),
    map(f,s), ord(c), pow(x,y), range(...), sum(s),
    type(obj)


Other Interesting Bits

• PyMite only supports 8-bit character strings, so no
Unicode

• PyMite supports 32-bit signed integers, floats (if
enabled) but not longs

• You can't override type operators. Eg '__add__()'
doesn't override '+'


Installing under Ubuntu 11.04

The easiest way to get PyMite is to check it out using Mercurial:
$ hg clone https://code.google.com/p/python-on-a-chip/

Install Python 2.6, setuptools and virtualenv
$ sudo apt-get install python2.6 python-setuptools
$ sudo easy_install virtualenv

Create the virtual environment and activate it
$ virtualenv -p python2.6 --no-site-packages ./pymite
$ source pymite/bin/activate


Windows? Almost

Download GNU Make, Python 2.6, SetupTools, and VirtualEnv
http://gnuwin32.sourceforge.net/packages/make.htm
http://www.python.org/getit/releases/2.6.6/
http://pypi.python.org/pypi/setuptools

Install and add their paths to your Path Environment Variable
c:Python26
c:Python26Scripts
c:Program FilesGnuWin32bin

Install and activate VirtualEnv
> easy_install.exe virtualenv
> virtualenv.exe --no-site-packages c:pymite
> c:pymiteScriptsactivate.bat

And then you install a C compiler...

Interactive Prompt

To compile for the desktop and launch the interactive prompt
$ make ipm

(make sure you have activated the Python2.6 VirtualEnv)
Test it out
ipm> class Robot():
.... def walk(self, direction):
.... print "Walking %s" % (direction,)
....
ipm> pybot = Robot()
ipm> pybot.walk("to the shops")
Walking to the shops


Microcontrollers?

mBed Microcontroller

• 32-bit ARM Processor

• Built-in USB interface

• Powered via USB

• Implements a Mass Storage Device, so programming is as
easy as copying the binary onto the Flash drive

• Many peripherals eg Ethernet, USB, Can, SPI, etc…

• Online Compiler

Robots!

m3pi from Pololu

•Easy to set up

•Ideal for getting started

•Cost:
– m3pi Robot $150 USD

– mbed Micro $60 USD

•Surprisingly Fast!!


What about Wireless?

Nobody likes to follow their robot around with a laptop…

The m3pi has a handy slot for a Digi Zigbee module.

But these $35 WiFi modules fit in the same slot:

RN-XV from Roving Networks
http://rovingnetworks.com/XVee.php

• Have the same pin-out
• Support WPA2
• Make the project awesome!


Putting it all together

Compile PyMite for the mbed target
$ make PLATFORM=mbed

Import the resulting .zip archive into the mbed IDE

Import the m3pi library into the mbed IDE

Compile and save the binary onto the mbed microcontroller

Turn on the Robot and connect to the ipm using a python
socket
$ tools/ipm.py –-ipaddress 192.168.1.3 –-port 2000


Thank You

Any Questions?


Python on a chip

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