Analysing the Control Software of the Compact Muon Solenoid Experiment at the Large Hadron Collider

TL;DR

This paper presents a formal analysis of the control software for the CMS experiment at CERN, using process algebra and tooling to verify finite state machine properties in a complex, hierarchical system.

Contribution

It introduces a formal description of the experiment's control software using mCRL2 and develops verification tools for analyzing finite state machines.

Findings

Successful formalization of 30,000+ state machines

Verification of subsystem properties through formal methods

Enhanced understanding of complex hierarchical control software

Abstract

The control software of the CERN Compact Muon Solenoid experiment contains over 30,000 finite state machines. These state machines are organised hierarchically: commands are sent down the hierarchy and state changes are sent upwards. The sheer size of the system makes it virtually impossible to fully understand the details of its behaviour at the macro level. This is fuelled by unclarities that already exist at the micro level. We have solved the latter problem by formally describing the finite state machines in the mCRL2 process algebra. The translation has been implemented using the ASF+SDF meta-environment, and its correctness was assessed by means of simulations and visualisations of individual finite state machines and through formal verification of subsystems of the control software. Based on the formalised semantics of the finite state machines, we have developed dedicated tooling for checking properties that can be verified on finite state machines in isolation.