A System for Exchanging Control and Status Messages in the NOvA Data Acquisition

In preparation for NOvA, a future neutrino experiment at Fermilab, we are developing a system for passing control and status messages in the data acquisition system. The DAQ system will consist of applications running on approximately 450 nodes. The message passing system will use a publish-subscribe model and will provide support for sending messages and receiving the associated replies. Additional features of the system include a layered architecture with custom APIs tailored to the needs of a DAQ system, the use of an open source messaging system for handling the reliable delivery of messages, the ability to send broadcasts to groups of applications, and APIs in Java, C++, and Python. Our choice for the open source system to deliver messages is EPICS. We will discuss the architecture of the system, our experience with EPICS, and preliminary test results.