MeerKAT Tango integration and experimentation

Work relating to the use of tango in MeerKAT (MKAT) and for SKA. This package contains:

simulators: Simulators of "real" telescope devices with TANGO interfaces. They can be used to test a telescope control system in a simulated environment without having to use any "real" hardware.
translators: Components that allow bidrectional communications between KATCP and TANGO based control systems. Also provides some helper utilities for integrating TANGO components into the MKAT system.

Simulators

Weather simulator

The weather simulator is built using tango_simlib . It provides the tango Weather device class. The weather simulator's behaviour can be modified by attaching a standard SimControl class to it. The SimControl class must run in the same device server instance as the Weather class. The SimControl class finds the Weather instance by getting its name from the model_key property. Most of the weather simulator attributes are implemented as GaussianSlewRateLimited quantities.

Example of starting a weather simulator with a SimControl instance using tango_launcher

mkat-tango-tango_launcher --name mkat_sim/weather/2 --class Weather\
                        --name mkat_simcontrol/weather/2 --class SimControl\
                        --server-command mkat-tango-weather-DS --port 0\
                        --server-instance tango-launched\
--put-device-property  mkat_simcontrol/weather/2:model_key:mkat_sim/weather/2

MKAT TANGO AP simulator

The actual MKAT antenna positioner (AP) devices have KATCP interfaces. To aid testing and development of the MKAT CAM (i.e TM) system, a fairly detailed simulator that mimics the MKAT AP behaviour and exposes a TANGO interface was developed.

Translators

tangodevice2katcp

Allows a KATCP client to talk to a TANGO device. Translates TANGO commands to KATCP requests and TANGO attributes to KATCP sensors. Subscribes to all attribute events and sets up polling if neccesary.

Example of launching a translator that connects as client to the Tango device mkat_sim/weather/1 and exposes it as a KATCP device server listening on TCP port 2051

mkat-tango-tangodevice2katcp --katcp-server-address :2051 mkat_sim/weather/1

Types

KATCP and TANGO both have defined data types, but the KATCP protocol (being text based) has less strict definitions. E.g. KATCP only defines a singular integer type with no specific bounds, while TANGO distinguishes between signed and unsigned, and between 8, 16, 32 or 64-bit integers. The KATCP library does, however, provide features for enforcing bounds and other checks on typed quantities, and these are used to enforce the appropriate bounds. E.g. if the TANGO device exposes a command that takes an 8-bit unsigned integer parameter, the KATCP translator will enforce the corresponding KATCP parameter to have a value of between 0 and 255.

Limitations

Easily removable limitations:

Does not handle TANGO commands that take or return arrayed values.

More difficult limitations:

Does not support IMAGE attributes. KATCP does not define how sensors with 2-D arrayed values should be handled.

Note:

For SPECTRUM attributes, the 1-D array is decomposed into individual KATCP sensors and the indices are appended to the end of the names of the generated sensors e.g. test.0, test.1 etc.

katcpdevice2tango

Allows a TANGO client to talk to a KATCP device. Currently only translates KATCP sensors to TANGO attributes. Sets up event strategies on all KATCP sensors so that all updates are received. The KATCP server is located by reading the TANGO device property katcp_address.

Example of launching a translator that connects as client to the KATCP device running on host localhost, TCP port 5000 and exposing it as a TANGO device named katcp/basic/1

mkat-tango-tango_launcher --name katcp/basic/1 --class TangoDeviceServer\
--server-command mkat-tango-katcpdevice2tango-DS --server-instance basic\
--port 0 --put-device-property katcp/basic/1:katcp_address:localhost:5000

If katcp/basic/ is already registered in the tango DB (class: TangoDeviceServer, device server mkat-tango-katcpdevice2tango-DS, property katcp_address = localhost:5000, server instance: basic)

mkat-tango-katcpdevice2tango-DS basic

tango_launcher

A helper script (mkat-tango-tango_launcher) is provided for registering, setting device properties, and starting a TANGO device server in a single step. This is useful when starting a TANGO device in the MKAT system, since the MKAT system has no direct understanding of the TANGO database and manages system interconnections through command-line parameters when starting various telescope processes. MKAT also has its own TCP port allocation method, which could conflict with the TANGO system's automatic port allocation. For this reason mkat-tango-tango_launcher requires a --port flag to be passed, controlling the TCP port where the TANGO device server will listen. To use the standard TANGO port allocation, use --port 0.

Run mkat-tango-tango_launcher --help for more information, or see examples in the sections above.

Notes on running tests

TANGO segfaults when restarting a device main function

PyTango segfaults if a device server is started more than once in a single process. This means that it is not possible to start/stop a tango device server as part of a test fixture. To work around this, the nose process plugin along with the tango.test_context module is used. Adding --processes=1 --process-restartworker --process-timeout=300 to a nose command line will cause each test tango device class (tango device fixtures are handled per-class) to be run in a new process.

Events and Polling

To run tests speedily, it is useful to have attributes refresh as quickly as possible, hence the polling period is set faster than usual. It was noted that when polling at a period of less than 50 ms, updates become inconsistent. I.e. the observed time difference between updates fluctuates (50+-20 ms), and sometime updates are skipped.

Periodic event type: An event is sent at a fixed periodic interval. The frequency of this event is determined by the event_period property of the attribute and the polling frequency. The polling frequency determines the highest frequency at which the attribute is read. This event_period determines the highest frequency at which the periodic, or any other, event is sent.

Docker images for development and testing

Introduction

Docker containers are useful for developing mkat-tango locally due its package requirements. This provides the information on how to , and the Docker images provide a similar environment to that used by Jenkins for the Continuous Integration tests.

Building the Docker image

Run commands like the following:

docker build -t mkat-tango .

Access a bash shell inside the docker container

docker run -ti mkat-tango '/bin/bash'

Using a container with an IDE

Once the image has been built, it can be used with IDEs like PyCharm (Professional version only)

PyCharm(with Dockerfile):

Add a new interpreter:

Open the Add Interpreter... dialog
Select Docker
Pick the image to use, e.g., mkat-tango:mkat-tango
Select python interpreter python2 or python3

PyCharm(with docker-compose):