Jacques Altaber

Suggested Principles for the Control of Future Accelerators

The SPS at CERN has a control system which incorporates a number of features which were novel at the time of its design 1). This system has been in use for the commissioning and operation of the accelerator and its experimental areas over the last three years, during which time considerable experience has been gained, and some modifications and changes have been made 2). Some of the principles have been adopted for subsequent control systems for accelerators and other processes, with various modifications to suit the particular circumstances. The purpose of this paper is to combine this experience with the predicted trends in microprocessor electronics to suggest a direction in which the design of control systems for large processes of this type may go. We will start with a brief description of the main features of the present system.

A Multiprocessor Bus Architecture for the LEP Control System

The architecture and the system aspects of the multi-master bus used for the construction of the process computer assemblies and the message handling assemblies of the LEP control system are presented. This bus architecture provides a fully distributed reservation mechanism and a protected access of the peripherals to prevent processor interferences. To achieve this, a channel concept is proposed, using a system bus for communication between processors and with their peripherals. The architecture is microprocessor independent, provides dynamic bus allocation amongst several microcomputers, offers processor position independence and has a multimaster bus extension to several crates with a homogeneous addressing. A global system concept, called E3S, has been developed including the definition of software primitives. The bus access software is organised in a layered structure matching the module functionality.

Accelerator Control Systems without Minicomputers

A paper given last year described in general terms a plan for the control of a large machine using assemblies of microcomputer units which simulate a conventional minicomputer by multiprocessing. In every other way the SPS control philosophy is followed. The design of a model assembly has allowed us to learn something about the protocols needed inside and between assemblies, as well as to assess more accurately what level of technology it is reasonable to apply. In any control system of this kind it would be desirable to allow engineering contributions from a variety of sources, and yet ensure the homogeneity needed for the system to remain reliable and comprehensible. Methods of achieving this are discussed.

An Interpretive Approach for Interactive Real-Time Control Through a Network

Abstract The CERN Super Proton Synchrotron (SPS) accelerator represents a large industrial control problem, with the additional complication that the control strategies are not fixed. Right from the beginning, it was decided to use an interpretive language for the control process. The main goal of this approach was to reduce the amount of programming effort needed for a proper control of the accelerator, by allowing the actual users — physicists, engineers and technicians — to write the control programs they needed. It very quickly appeared that this method was ideal for providing interactive tools for a control system based on a network. The requirement for interactive network control has been implemented by leaving to the user the choice of those parts of the network best suited for the execution of sections of his program. For that reason interpreter instructions have been defined, allowing the user to define where in the network a logical unit of his algorithm should be executed, and where individual items of the data should be stored. This strategy allows easy access to all the hardware through a distributed data-base. The interpreter being basically a string handler, equipment control can be packed into a module which is called from the program through a name with a standard input-output scheme. All this allows algorithm exportation, while network transfers are minimized. Such a system has been in operation since 1976. Many non-professional programmers are regularly writing or modifying ‘network procedures’ for ever-changing control purposes. The simplicity and flexibility of the interpretive method has enabled many technical innovations to be installed over the years, and some of these are described.

The Message Architecture of the LEP Control System

The LEP control system will be constructed as a global communication system where microprocessors will be used everywhere, from the management of the communication mechanisms, the execution of complex control procedures, and the supervision of the equipment. To achieve this, the global control problem has been cut into sizeable functions which will be encapsulated into microprocessor modules containing enough hardware for the function to be mostly self-contained. This leads to a function architecture where messages are exchanged between the functions on miscellaneous media. It will be shown how these message exchanges can be organized into a uniform flow of data all through the system.

Multi-microprocessor architecture for the LEP storage ring controls

Abstract The new CERN Large Electron Positron (LEP) storage ring control system follows the concepts developed for the Super Proton Synchrotron (SPS) accelerator but making use of present day technology. A multi-tasking computer is replaced by an assembly of microprocessor based modules performing a unique, single stream type of task. Each module is a general purpose processing unit (GPU) containing a 68000 microprocessor, private memory, protected memory accessible by others GPUs, a programmable and adressable interrupt logic and a distributed arbitration mechanism. Communication amongst GPUs is done by a message protocol, the medium being the VME multi-master parallel bus. Dedicated Input/Output modules can be associated privately with the GPUs thus forming specialized functional modules, or providing additional private memory. All these functional modules communicate over the VMEbus in a protected access mode with resource reservation to prevent processor interferences. A global system concept has been developed which will be detailed in this paper. The improvement in performance, flexibility, processor independence, minimization of integration effort required, as well as error diagnostics in such a multiprocessor architecture are also discussed.

ESSENTIAL FEATURES OF THE CERN SPS DISTRIBUTED CONTROL SYSTEM

ABSTRACT The SPS accelerator presents a considerable industrial control problem with the additional complication that the control procedures are never fixed. Right from the beginning it was decided to base the control system on a distributed network making use of an interpretive language for the control processes. The success of these decisions can be seen from the fact that over the last six years, the system has grown to a network of more tha~ 50 computers spread over a ten square kilometer site, all the time controlling an ever-changing accelerator complex. This paper will discuss the major elements of the strategy used and explain the reason for their choice. Microprocessors have become very popular in the field of. industrial control and the SPS control system is going to integrate this trend with little difficulty. The paper will show that the SPS approach is ideally suited to the construction of a real-time control network making use only of microprocessor based units.