• V. H. Gyurjyan, D. Abbott, W. G. Heyes, E. Jastrzembski, C. Timmer, E. J. Wolin
  JLAB, Newport News, Virginia
• B. Moffitt
  Thomas Jefferson National Accelerator Facility (JLAB), Newport News, Virginia

The future high energy and nuclear physics experiments will require experiment control systems that operate at a higher level of automation, flexibility, and robustness. In this paper a multi-agent system based framework (AFECS) is presented as an alternative methodology to control large-scale experiments. AFECS creates a control system environment as a collection of software agents behaving as finite state machines. These agents can represent real entities, such as hardware devices, software tasks, or control subsystems. AFECS agents can be distributed over a variety of platforms. Agents communicate with their associated physical components using range of communication protocols, including tcl-DP, cMsg (publish-subscribe communication system developed at Jefferson Lab), SNMP (simple network management protocol), EPICS channel access protocol and JMS.

• E. J. Wolin, D. Abbott, V. H. Gyurjyan, W. G. Heyes, E. Jastrzembski, D. Lawrence, C. Timmer
  JLAB, Newport News, Virginia
• W. Gu, B. Moffitt
  Thomas Jefferson National Accelerator Facility (JLAB), Newport News, Virginia

A speaker* at ICALEPCS 2007 advocated the decoupling of control system components through the use of asynchronous communications. The cMsg package from the Jefferson Lab DAQ group implements true publish/subscribe communications using a narrow interface that meets most of the requirements outlined in the talk referenced earlier. Decoupled or loosely-coupled communication ensures that changes to one part of a control system have no effect on other parts of the system. Asynchronous communication eliminates needless waits and timeouts. And the flexibility of the subscription space and the ability to transmit arbitrary information allows cMsg to be used for virtually any type of control application, including run control, logging, monitoring, hardware control, alarm systems, etc. In this paper we describe how publish/subscribe works, how it differs from client/server communications, and how asynchronous publish/subscribe communications allows for decoupling. We further describe the cMsg package and its narrow API, how it was designed for simplicity and ease of use, how we use it in control systems at JLab, and how we integrate cMsg with EPICS Channel Access.

* Stephen A, Lewis, "Elements of Control System Longevity", Proceedings of ICALEPCS 2007, Knoxville, TN, US.