Poverty, a quasar extension module

by Piotr P. Nikiel piotr@nikiel.info

What is this?

Quasar is an open-source framework for rapid creation of OPC-UA software components.

Poverty (this project) is an extension module of Quasar. It solves the problem of loading your quasar-made OPC-UA servers from a Python program with a Python interface which supports:

• controlling the server (start it, stop it, etc ...)
• "operate" its Address-Space, i.e. publish data via OPC-UA from that Python program or read the cached data.

Basic usage mode

Note: tested with quasar version nebula.B1 (shall correspond to 1.5+)

1. Steps to do in your quasar project
   1. add -fPIC in the add_definitions of your build config
   2. in ProjectSettings.cmake (root of your quasar project):
      1. set BUILD_SERVER_SHARED_LIB to ON.
      2. add Poverty to CUSTOM_SERVER_MODULES.
      3. add python3 to ADDITIONAL_BOOST_LIBS.
      4. set POVERTY_STRICTLY_PYTHON3 in case your system can have both python2 and python3 (most systems). I.e. your system needs to have python3-config command visible!
   3. Poverty current only works with open62541 backend of quasar. Thus if you are with UA-SDK, switch to open62541.
2. clone Poverty (this GitHub repo) in your quasar project, or add it as a git submodule,
3. build your OPC-UA server (e.g. ./quasar.py build)

To test it:

1. in your quasar project, copy the test python script Poverty/extra/test.py into build/bin
2. copy, or symlink, build/Poverty.so into build/bin
3. run the test program: python3 test.py

Distributing your Poverty+quasar based OPC-UA server

You need the following files in your target application:

• Poverty.so (builds in build/Poverty)
• libOpcUaServer.so (builds in build/bin)
• the particular config file of the server (which has instanced of quasar objects ...), normally called config.xml
• the particular ServerConfig.xml where stuff like endpoints and OPC-UA certificates are defined.

Why Poverty and not a custom, pure Python OPC-UA solution?

There are reasons to use Poverty rather than a pure-Python OPC-UA solution:

• by embedding a quasar made server, you enter the quasar ecosystem which will bring you benefits of other quasar modules. For example, you could quickly do WinCC OA integration (Cacophony quasar module) or generate C++ clients (UaObjects for Quasar) or so.

• by making a quasar-based OPC-UA you use carefully tested OPC-UA components, same as these used in for example LHC experiments controls at CERN.

Why not to use Poverty?

There are also reasons that might prevent you from using Poverty:

• currently, there is no possibly of any call-backs into Python.
• some data types are not supported from Python yet, for example OPC-UA arrays.