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Troup, E., Garrington, S. T., McKay, N. P. F., & Noble, R. G. 2000, in ASP Conf. Ser., Vol. 216, Astronomical Data
Analysis Software and Systems IX, eds. N. Manset, C. Veillet, D. Crabtree (San Francisco: ASP), 291
The MERLIN Correlator Software Project
E. Troup, S. T. Garrington, N. P. F. McKay, R. G. Noble
Jodrell Bank Observatory, University of Manchester, Macclesfield, SK11
9DL, UK
Abstract:
The MERLIN
1array is being upgraded with new correlator hardware and improved
monitoring, operating and control software. The aims of the upgrade are
to provide easy to use display and monitoring of all components of
MERLIN, including the astronomical data, to improve reliability and to
assist the MERLIN controllers in data quality monitoring. The project
design is based around object-oriented techniques and is being coded in
C++.
The project is being developed using elements of the
JIVE
correlator
software, also designed at Jodrell Bank.
The MERLIN array is a network of radio telescopes connected by microwave
links into a real-time interferometer. The radio telescopes are
located in England and controlled from Jodrell Bank Observatory via
land lines. A small team of operations staff schedule the running of
the array while controllers monitor the operation and safety of the
telescopes while the system is in use. The observing system is under
the overall control of a computer attached to the correlator and this
computer is responsible for sequencing the observations, configuring
the correlator and accumulating the correlated data. The project aims
to improve the reliability and efficiency of MERLIN operations by
upgrading the real-time correlator control computer and providing new
software for aiding astronomical data-quality and array subsystem
monitoring. The software is being designed using object-oriented
methods and is written in C++. Software analysis has proceeded using the
methodology described in Rumbaugh et al. (1991).
Wherever possible, the MERLIN upgrade project intends to re-use
software designed for the European VLBI Network
MkIV correlator.
The aims of the project include providing the following features:
- Correlator upgrade:
Install a new real-time control processor for the correlator.
Install a workstation to configure, control and monitor the system.
Re-use or adapt JIVE/EVN correlator software where possible.
- Array Monitoring:
A graphical display of the array including telescopes, modems,
L-band and microwave links.
- Data Analysis:
Scripts for the operators to automate the quality control of data
from calibrator scans.
Check and report on telescope gain, polarization performance, closure
phase, etc.
- Data Display:
Display correlation (amplitude and phase) for each baseline. Display
lag data in real time. Scrolling display of a single frequency
channel or the average of several channels.
- Data Processing and Archive:
Operators to scrutinize the majority of data within a few days. Scripts
to automate processing e.g. calibration, phase-referencing and
imaging. Operators will also be responsible for archiving the data
and maintaining the database of completed observations.
- Scheduling:
Flexible scheduling so that the controllers can reschedule important
scans if weather or equipment cause problems. The operators need a
simple view of the current schedule with highlighting for high
priority scans.
The development of the system has begun using software and software
models developed for the JIVE correlator, as well as MERLIN-specific
code. A large amount of work is still to be done, but the availability
of well-tested class libraries has sped up development and prototyping.
An example of an application developed for MERLIN is shown in
Figure 1.
Figure 1:
Real-time correlator data display.
 |
This display is the output from a test correlator and was built using
shared memory classes derived from JIVE classes and the Qt and Qwt
class libraries.
The class libraries being used to implement the MERLIN software
include the following:
- Shmem_Shared
- Using the Shmem_Shared class as a base, any
derived classes will reside in shared memory. Shared memory classes
can be used for fast, efficient transfer of bulk data, such as
correlator output data or monitor data between Jobs.
- Message
- The Message class is designed to implement a machine-
and transport-independent interprocess communication class. This is
used for such things as sending commands or the response to commands
between processes.
- Threads
- The Threads classes are used to implement concurrent
streams of control within a process.
- State_Machine
- The State_Machine class provides a framework for
building a state machine within a process. It can be used in
conjunction with the Threads classes to implement the states and
transitions of a software dynamic model.
- Utility
- A number of utility classes including a hash-table
class and a circular buffer class.
- Qt Free Edition
- Qt is a user-interface C++ class library produced by
TrollTech. It includes a
wide range of widgets and is designed for ease of use and customization.
- Qwt
- Qwt
is a widget set based on Qt and provides x-y graph
displays with both log and linear scales and includes scrollable data
plots that can be used for real-time data.
References
Rumbaugh, J., Blaha, M., Premerlani, W., Eddy, F., &
Lorensen, W. 1991, Object-Oriented Modeling and Design (New Jersey: Prentice Hall)
Footnotes
- ... MERLIN1
- MERLIN, The Multi-Element Radio Linked
Interferometer Network is operated by the University of Manchester on
behalf of PPARC
© Copyright 2000 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA
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