The CEBAF Control System

CEBAF has recently upgraded its accelerator control system to use EPICS, a control system toolkit being developed by a collaboration among laboratories in the US and Europe. The migration to EPICS has taken place during a year of intense commissioning activity, with new and old control systems operating concurrently. Existing CAMAC hardware was preserved by adding a CAMAC serial highway link to VME; newer hardware developments are now primarily in VME. Software is distributed among three tiers of computers: first, workstations and X terminals for operator interfaces and high level applications; second, VME single board computers for distributed access to hardware and for local control processing (complex sequences, limit checking, some process control); third, embedded processors where needed for faster closed loop operation. In some cases, multiple VME processors transparently access a single serial highway for improved performance. This system has demonstrated the ability to scale EPICS to controlling thousands of devices, including hundreds of embedded processors, with control distributed among dozens of VME processors executing more than 125,000 EPICS database records. To deal with the large size of the control system, CEBAF has integrated an object oriented database, providing data management capabilities for both low level I/O (calibration, alarm limits, etc.) and high level machine modelling (optics properties, etc.). A new callable interface which is control system independent permits access to live EPICS data, data in other Unix processes, and data contained in the object oriented database (extensible to other sources).