ANL, Argonne
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
With the Experimental Physics and Industrial Control System (EPICS) toolkit being used around the world, modifications to the core software must be very carefully designed to avoid breaking existing applications; this often limits the changes and new functionality that can be introduced. A new way to extend the EPICS input-output controller (IOC) was discovered recently that should be fully compatible with most channel access (CA) client programs; if the IOC supports optional postfix modifiers to the process variable (PV) field names it publishes, it becomes possible to add several features to the EPICS toolkit. However if those field modifiers can be written in standard JavaScript Object Notation (JSON) syntax they can encode a complex data structure and become very powerful, permitting client-specific configuration of individual CA channels without necessitating any changes to the network protocol. This paper will describe how EPICS Base is adding support for JSON encoding and field modifiers, and will discuss other features such as record aliases that have been introduced to help control systems evolve.
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
BNL, Upton, Long Island, New York
ANL, Argonne
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.