REPLACEMENT OF OUTDATED VME BOARDS AS STARTING POINT FOR CONTROL SYSTEM MODERNIZATION
L. Hechler, K. Höppner, P. Kainberger, U. Krause, Gerhard Schwarz · 2005
Control systems are operational for quite a long time, easily spanning more than a decade. Along the way facilities are extended and operations are more and more refined. The control system has to be modified and extended accordingly. This has to be done on the background of rapidly evolving technology. Hardware components and software products on which the system originally was based are no longer available while progress in the IT area eases implementing additionally requested features. Preparation for continuous evolution was not a primary aspect in the design of the GSI control system. As a consequence, introduction of new hard- and software components were avoided whenever possible. The system depends on many components which dated from the beginning of operation. Replacing a no longer available VME board was taken as an occasion for a general renovation of the system. Rebuilding the middle layer of the control system allows much simpler integration of new components and prepares the system for future extensions. PRESENT GSI CONTROL SYSTEM Architecture The control system was designed as a decentralized distributed system (Fig. 1), according to the nowadays well established standard model. The accelerator's equipment is connected by a field bus to front-end controllers which communicate by Ethe rnet with operation workstations. M68020 VME boards are used at the front-end level while the operations level uses OpenVMS Alphas. In contrast to many other systems; the front end side is divided in two layers, device presentation computers (DPC) as access points for operations requests and equipment control (EC) computers to service the devices. Assigning the tasks to different processors eases ensuring precisely timed device control. Synchronized by signals from the timing system, only the ECs have to implement real-time functionality.