An integrated computer control system for the ANU linac

One facet of the installation of the superconducting linac at the ANU is the need for computer control of a variety of systems, such as beam transport, resonator RF, cryogenics and others. To accommodate this, a number of control interfaces (for example, analogue signals and RS232 serial lines) must be employed. Ideally, all of the systems should be able to be controlled from a central location, remote from the actual devices. To this end a system based around VAX computers and VME crates has been designed and is currently being developed and implemented. A VAXstation is used to issue control messages and perform high-level functions, while VME crates containing appropriate modules (primarily DACs, ADCs and digital I/O boards) control the devices. The controllers in the VME crates are AEON rtVAX modules running a real-time operating system. Communication with the VAXstation is via DECnet, on a private ethernet to allow communication rates unaffected by unrelated network activity and potentially increasing the security of the system by providing a possible network isolation point. Also on this ethernet are a number of terminal servers to control RS232 devices. A central database contains all device control and monitoring parameters. The main control process running on the VAXstation is responsible for maintaining the current values of the parameters in the database and for dispatching control messages to the appropriate VME crate or RS232 serial line. Separate graphical interface processes allow the operator to interact with the control process, communicating through shared memory. Many graphics processes can be active simultaneously, displaying either on a single or on multiple terminals. Software running on the rtVAX controllers handles the low-level device-specific control by translating messages from the main control process to VME commands which set hardware outputs on VME modules. Similarly, requests for the value of a parameter result in the rtVAX program interrogating VME input modules, and returning the result to the main control process. In the near future, this system will be extended to control most of the 14UD accelerator, in addition to thelinac. At present the system also controls one of the two ion sources that provide beam to the 14UD.