State Notation Language and Sequencer

Maintainer:Ben Franksen <benjamin.franksen@helmholtz-berlin.de> Bug Reports:tech-talk@aps.anl.gov

Welcome to the home page of the EPICS Sequencer project.

This page contains the documentation, including instructions how to download, build, and install the software.

This project is a component of the Experimental Physics and Industrial Controls System, short EPICS. EPICS is a system of interactive applications, development tools, and a common run-time environment that allows users to build and execute real-time control and data acquisition systems for experimental facilities, such as particle accelerators and telescopes.

The state notation language SNL allows programming sequential operations that interact with EPICS process variables without the usual complexity involved with task scheduling, semaphores, event handling, and I/O programming. The language is a restricted subset of C, enhanced with extra syntax for descibing state sets, states, state transitions, and the binding of program variables to named and anonymous process variables. See the Tutorial for a gentle introduction.

From the SNL source code, the SNL compiler snc generates a number of C code procedures that are called by the run-time sequencer, a C library contained in this project. This library handles all low-level management of connecting, monitoring, and changing process variables, as well as task (thread) creation and communication. The sequencer interfaces to the underlying control system through a generic PV (process variable) API that supports, among other message systems, the Channel Access facility of EPICS.