Slides for my presentation "Python on a chip" at KiwiPycon 2011.

1. 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

2. 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
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

3. 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
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

4. 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)
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

5. 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
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

6. 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
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

7. 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)
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

8. 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 '+'
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

9. 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
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

10. 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...
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

11. 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
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

12. 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
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

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

14. Robots!
m3pi from Pololu
•Easy to set up
•Ideal for getting started
•Cost:
– m3pi Robot $150 USD
– mbed Micro $60 USD
•Surprisingly Fast!!
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

15. 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!
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

16. 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
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz

17. Thank You
Any Questions?
Kiwi Pycon 2011 Python on a Chip jeremy@stott.co.nz