tango-simlib: Easily generate TANGO device simulators¶

Introduction¶

tango-simlib is a library that aids the data-driven development of TANGO device simulators. It aims to make it easy to develop basic simulators while making it possible to implement more complex simulators. In addition to the simulated device interface, a separate TANGO simulation-control interface is generated, allowing the simulator to be manipulated via a back-channel to simulate e.g. failure conditions on the simulated device interface.

Using only the basic TANGO interface description captured via a POGO generated XMI file, a basic simulator with randomly varying attributes and no-op command handlers can be generated with no further coding. Attribute simulation parameters and simple command behaviour can be specified using a Simulator Description Datafile (SIMDD). The format of this file is currently a working proposal and subject to change. A more formal format specification is being worked on.

Note that tango-simlib does not generate simulator code. Rather, the simulator’s behaviour is driven by the description data at run-time using Python‘s dynamic programming features. If the description files (XMI or SIMDD) are modified, the simulator device server only needs to be restarted for the changes to take effect.

Rationale¶

During the development of the control and monitoring (CAM) systems for the KAT-7 (KAT-7-wiki) and MeerKAT (MeerKAT-wiki) at SKASA it was found that having control-interface simulators available for all hardware and subsystems that CAM needs to control and monitor is an incredibly valuable resource. In early CAM development it:

Makes it possible to start developing the CAM system before hardware or vendor-provided hardware simulators are available.
Allows gaps in interfaces to be identified early on in the development process.

As development progresses, the full, actual, MeerKAT/KAT-7 CAM is run against the simulated devices, allowing CAM functionality to be tested without the need of real telescope hardware. The simulators also expose a back-channel that can be used to modify the behaviour of the simulators during tests e.g. to simulate error conditions. This is exploited by CAM developers in their own development environments for day to day development tasks and also allows daily automated functional integration tests to be run. It was also found that initially having even a very simple simulator available is quite valuable, and that for many devices the simple simulator is always sufficient.

The KAT-7 and MeerKAT telescopes use the Karoo Array Telescope Control Protocol (KATCP) for inter-device, subsystem and component communications. In light of that a library was developed that makes it very easy to code a basic simulator, providing no-op command (KATCP request) handlers and randomly varying attribute (KATCP sensor) values along with the back-channel interface for “free”.

The planned SKA telescope project that the SKASA team is participating in has decided to standardise on the TANGO control systems framework. This library is an attempt to bring the same simulation approach used for the KAT-7 and MeerKAT telescope to the TANGO world.

Basic Usage¶

Installation¶

Note that installation requires the TANGO binary prerequisites to be installed. If you cannot install the PyTango package you will not be able to install tango-simlib.

Installation from source, working directory where source is checked out

$ pip install .

This package is available on PYPI, allowing

$ pip install tango-simlib

Device Simulators¶

Generating Simulators¶

The basic way of generating a TANGO device simulator using this library is to make use of the TANGO simulator generator module. Give it a path to the description files (XMI or SIMDD or both).

$ tango-simlib-generator --sim-data-file Weather.xmi\
                         --dserver-name weather-DS\
                         --directory .

This will generate a python executable file in your current working directory named weather-DS.

In order to run this generated device simulator code, you can execute the tango-launcher script, a helper script which will register the TANGO device server, setup any required device properties and in turn start up the device server process, all in one go.

$ tango-simlib-launcher --name mkat_sim/weather/1 --class Weather\
                        --name mkat_simcontrol/weather/1\
                        --class WeatherSimControl\
                        --server-command weather-DS --port 0\
                        --server-instance tango-launched\
                        --put-device-property mkat_simcontrol/weather/1:model_key:mkat_sim/weather/1

Ready-made Simulators¶

Weather simulators¶

A code snippet of starting the Weather simulator generated from the Weather.xmi file with a SimControl instance using the tango_launcher.py script. Change directory to tango_simlib/examples/

$ tango-simlib-launcher --name mkat_sim/weather/1 --class Weather\
                        --name mkat_simcontrol/weather/1\
                        --class WeatherSimControl\
                        --server-command weather1.py --port 0\
                        --server-instance tango-launched\
                        --put-device-property mkat_simcontrol/weather/1:model_key:mkat_sim/weather/1

An example of starting the Weather simulator generated from the Weather_SIMDD.json file with a SimControl instance using the tango_launcher.py script.

$ tango-simlib-launcher --name mkat_sim/weather/2 --class Weather\
                        --name mkat_simcontrol/weather/2\
                        --class WeatherSimControl\
                        --server-command weather2.py --port 0\
                        --server-instance tango-launched\
                        --put-device-property mkat_simcontrol/weather/2:model_key:mkat_sim/weather/2

MeerKAT Video Display System simulator¶

An example of starting the VDS simulator generated from both the MkatVds.xmi and the MkatVds_SIMDD.json files with a SimControl instance using the tango_launcher.py script.

$ tango-simlib-launcher --name mkat_sim/vds/1 --class MkatVds\
                        --name mkat_simcontrol/vds/1\
                        --class MkatVdsSimControl\
                        --server-command mkat_vds.py --port 0\
                        --server-instance tango-launched\
                        --put-device-property mkat_simcontrol/vds/1:model_key:mkat_sim/vds/1

Once the tango-simlib-tango-launcher script has been executed, the TANGO server will be created in the TANGO database. The TANGO device server will be registered along with its properties and the server process will be started. This will start the server instance which has the two classes Weather and WeatherSimControl registered under it, respectively, which in turn will start the devices from each of the TANGO classes.

Screenshots of Interfaces¶

This is what you would have in the TANGO DB once the device server has been registered

Figure 1. A snapshot of the TANGO DB viewed using JIVE - the TANGO-DB browser.

In this instance, we have the simulated device in an alarm state after executing the SetOffRainStorm command on the test device interface, or what we call the simulator controller.

Figure 2. A view of the sim device and its associated sim control interface using the TANGO Application ToolKit (ATK) client framework.