Mark Plesko

The ALMA common software: a developer-friendly CORBA-based framework

The ALMA Common Software (ACS) is a set of application frameworks built on top of CORBA. It provides a common software infrastructure to all partners in the ALMA collaboration. The usage of ACS extends from high-level applications such as the Observation Preparation Tool [7] that will run on the desk of astronomers, down to the Control Software [6] domain. The purpose of ACS is twofold: from a system perspective, it provides the implementation of a coherent set of design patterns and services that will make the whole ALMA software [1] uniform and maintainable; from the perspective of an ALMA developer, it provides a friendly programming environment in which the complexity of the CORBA middleware and other libraries is hidden and coding is drastically reduced. The evolution of ACS is driven by a long term development plan, however on the 6-months release cycle the plan is adjusted based on incoming requests from ALMA subsystem development teams. ACS was presented at SPIE 2002[2]. In the two years since then, the core services provided by ACS have been extended, while the coverage of the application framework has been increased to satisfy the needs of high-level and data flow applications. ACS is available under the LGPL public license. The patterns implemented and the services provided can be of use also outside the astronomical community; several projects have already shown their interest in ACS. This paper presents the status of ACS and the progress over the last two years. Emphasis is placed on showing how requests from ACS users have driven the selection of new features.

Application development using the ALMA common software

The ALMA Common Software (ACS) provides the software infrastructure used by ALMA and by several other telescope projects, thanks also to the choice of adopting the LGPL public license. ACS is a set of application frameworks providing the basic services needed for object oriented distributed computing. Among these are transparent remote object invocation, object deployment and location based on a container/component model, distributed error, alarm handling, logging and events. ACS is based on CORBA and built on top of free CORBA implementations. Free software is extensively used wherever possible. The general architecture of ACS was presented at SPIE 2002. ACS has been under development for 6 years and it is midway through its development life. Many applications have been written using ACS; the ALMA test facility, APEX and other telescopes are running systems based on ACS. This is therefore a good time to look back and see what have been until now the strong and the weak points of ACS in terms of architecture and implementation. In this perspective, it is very important to analyze the applications based on ACS, the feedback received by the users and the impact that this feedback has had on the development of ACS itself, by favoring the development of some features with respect to others. The purpose of this paper is to describe the results of this analysis and discuss what we would like to do in order to extend and improve ACS in the coming years, in particular to make application development easier and more efficient.

CORBA-based Common Software for the ALMA project

The Atacama Large Millimeter Array (ALMA) is a joint project between astronomical organizations in Europe and North America. ALMA will consist of at least 64 12-meter antennas operating in the millimeter and sub-millimeter range, with baselines up to 14 km. It will be located at an altitude above 5000m in the Chilean Atacama desert. The ALMA Common Software (ACS) provides a software infrastructure common to all partners and consists of a documented collection of common patterns and of components that implement those patterns. The heart of ACS is an object model based on Distributed Objects (DOs), implemented as CORBA objects. The teams responsible for the control system development use DOs as the basis for components and devices such as an antenna mount control. ACS provides common CORBA-based services such as logging, error and alarm management, configuration database and lifecycle management. A code generator creates a Java Bean for each DO. Programmers can write Java client applications by connecting those Beans with data-manipulation and visualization Beans. ACS is based on the experience gained in the astronomical and particle accelerator domains, and reuses and extends proven concepts and components. Although designed for ALMA, ACS can be used in other new control systems, since it implements proven design patterns using state of the art, stable and reliable technology. This paper presents the architecture of ACS and its status, detailing the object model and major services.

An embeddable control system for astronomical instrumentation

Large experimental facilities, like telescopes and focal plane instrumentation in the astronomical domain, are becoming more and more complex and expensive, as well as control systems for managing such instruments. The general trend, as can be learned by realizations carried out in the most recent years, clearly drives to most cost-effective solutions: widespread, stable standards in the software field, COTS (commercial off-the-shelf) components and industry standards in the hardware field. Therefore a new generation of control system products needs to be developed, in order to help the scientific community to minimize the cost and efforts required for maintenance and control of their facilities. In the spirit of the aforementioned requirements and to provide a low-cost software and hardware environment we present a working prototype of a control system, based on RTAI Linux and on ACS (Advanced Control System) framework ported to an embedded platform. The hardware has been chosen among COTS components: a PC/104+ platform equipped with a PMAC2A motion controller card and a commercial StrongARM single board controller. In this way we achieved a very powerful, inexpensive and robust real-time control system which can be used as a general purpose building block in the design of new instruments and could also be proposed as a standard in the field.