OpenWRT¶

This page describes how to get the relayr Python API running on OpenWRT, a popular open, minimized Linux distribution for embedded systems. One of the widely available boards running OpenWRT is the WRTnode which includes a WiFi controller and therefore seems especially well-suited for IoT applications.

Although OpenWRT is heavily minimized (running in only 16 MB of memory) it has its own package management system (see opkg -h) with dependancy tracking and many interesting packages, including a MQTT broker named Mosquitto. It is also a nice platform for Python (versions 2.7 and 3.4) since it provides many packages, either separate (big) ones from the Python standard library or by third parties, like even OpenCV!

Install or upgrade Python¶

Before installing the Python-SDK on OpenWRT a few additional steps are necessary to establish the baseline. If a Python interpreter is already installed it might well be Python 2.7.3. For security reasons it is recommended to replace this with Python 2.7.9 (or Python 3.4.3), or install it from scratch. Two extra packages are also needed, namely python-codecs and python-openssl (the names may have a python3- prefix if you prefer Python 3 - the relayr Python API runs on Python 2.7 and 3.4).

You can install these packages like this (shown here for Python 2.7):

opkg install python-base
opkg install python-codecs
opkg install python-light
opkg install python-openssl

Then you should see this list when asking for installed Python packages with opkg list-installed | grep python:

python-base - 2.7.9-5
python-codecs - 2.7.9-5
python-light - 2.7.9-5
python-openssl - 2.7.9-5

This will eat some of your memory, but you can include these packages into a custom firmware image (which will be heavily compressed) and flash your board with it in order to gain space, again, if you need it.

Install temporary tools¶

Since OpenWRT contains only minimal versions of some common GNU/Linux tools, we need to install the real ones in a preliminary step like this (first updating the package menagement system):

opkg update
opkg install wget tar

Later, when everything needed is installed, you can remove these packages and their dependancies again with:

opkg remove wget libpcre
opkg remove tar bzip2 libbz2 libacl

If, for whatever reasons, you don’t want to install these helpers, you can, of course, download a source code tarball on a normal machine and transfer the unpacked directory via scp -r to your board.

Install dependancies¶

The usual way of installing Python packages is pip or easy_install where the latter builds on the setuptools package, an alternative for the distutils package in the Python standard library. While there are opkg packages for pip and setuptools these are pretty heavy and bring in other dependancies. Therefore they are not used here, but instead all the dependancies for the relayr Python API are installed individually.

For the packages to build and install now it is recommended to create a source directory in the volatile RAM of your board (the WRTnode has 128 MB), for example like this:

mkdir /tmp/src
cd /tmp/src

MQTT¶

OpenWRT does not provide the Python package paho-mqtt, but it’s very simple to build and install from source:

wget --no-check-certificate https://pypi.python.org/packages/source/p/paho-mqtt/paho-mqtt-1.1.tar.gz
tar xfz paho-mqtt-1.1.tar.gz
cd paho-mqtt-1.1
python setup.py install
cd ..

You have successfully installed it if you can run this in Python without any error: import paho.

Requests¶

wget --no-check-certificate https://pypi.python.org/packages/source/r/requests/requests-2.7.0.tar.gz
tar xfz requests-2.7.0.tar.gz
cd requests-2.7.0
python setup.py install
cd ..

Certifi¶

wget --no-check-certificate https://github.com/certifi/python-certifi/archive/2015.04.28.tar.gz
tar xfz 2015.04.28.tar.gz
cd python-certifi-2015.04.28
cp -r certifi /usr/lib/python2.7/site-packages
cd ..

Miscellaneous¶

The remaining modules are not strictly needed for being able to use the relayr Python API, like termcolor (used in a demo). Or they are not strictly needed yet, like isodate.

wget --no-check-certificate https://pypi.python.org/packages/source/t/termcolor/termcolor-1.1.0.tar.gz
tar xfz termcolor-1.1.0.tar.gz
cd termcolor-1.1.0
python setup.py install
cd ..

wget --no-check-certificate https://pypi.python.org/packages/source/i/isodate/isodate-0.5.1.tar.gz
tar xfz isodate-0.5.1.tar.gz
cd isodate-0.5.1/src
cp -r isodate /usr/lib/python2.7/site-packages
cd ../..

relayr Python API¶

Since we don’t want to use pip or easy_install you can fetch a tarball from Github or PyPI and unpack it as usual. After that you need to copy the relayr folder manually into the site-packages folder as shown here for Python 2.7:

wget --no-check-certificate https://github.com/relayr/python-sdk/archive/0.3.0.tar.gz
# or wget --no-check-certificate https://pypi.python.org/packages/source/r/relayr/relayr-0.2.4.tar.gz
tar xfz 0.3.0.tar.gz
cd 0.3.0
cp -r relayr /usr/lib/python2.7/site-packages

If everything worked fine you can run e.g. these commands from the unpacked directory to test that the installation was successful:

python demos/api_pulse.py
python runtests.py tests/test_anonymous.py

If you edit the file tests/fixture_registered.py and provide IDs of your WunderBar you can run the entire testsuite like this: python runtests.py tests.

Digression on minimizing Python code¶

Code minimization is usually performed on Javacript libraries to reduce download times in webbrowsers. On embedded devices the precious resource is memory (on a WRTnode it’s 16 MB of flash user memory). Therefore, it can sometimes be helpful to reduce the size of any larger Python software to be installed, too, either by a third party or by yourself.

The recommended tool for minimizing Python code is pyminifier which in its simple forms will strip-off docstrings and comments and minimize the indentation of Python source files. You can use it on the relayr Python-SDK for example as follows, before installing it on OpenWRT:

pip install pyminifier
wget --no-check-certificate https://github.com/relayr/python-sdk/archive/0.3.0.tar.gz
tar xfz 0.3.0.tar.gz
cd 0.3.0
pyminifier *.py