Advanced Monitor/Subscription Mechanisms for EPICS
A.N.Johnson (ANL) L.R.Dalesio (BNL) R.Lange* (Helmholtz-Zentrum Berlin für Materialien und Energie GmbH Elektronen-Speicherring BESSY II)
Publish/subscribe systems need to handle the possibility that there are subscribers requiring notification at an update rate much lower than the publisher's natural frequency, or synchronized to external events. Feedback or pulse-to-pulse diagnostics are processed at rates in the 100Hz or even multi kHz range, while many subscribers will not be able to process the data at this rate: e.g. archiving, visualization, and processing clients each require specific, different update rates. Sending more updates than required wastes processor and network bandwidth. A subscriber should be able to specify rate limiting factors or filters that are instantiated and guaranteed by the publisher. Many accelerators, especially pulsed machines, are using a hardware event system to distribute fiducials and events from a central event and/or frequency generator. These events should be integrated into the publish/subscribe system to support posting event synchronous updates to subscribers that require synchronized data. This paper investigates several approaches to provide these functionalities in the EPICS architecture.
Work supported by U.S. Department of Energy (contracts DE-AC02-06CH11357 resp. DE-AC02-98CH10886), German Bundesministerium für Bildung und Forschung and Land Berlin.