  Programmable Logic Controllers (PLC) are widely used for industrial
automation including safety systems at CERN. The incorrect behaviour of the PLC
control system logic can cause significant financial losses by damage of
property or the environment or even injuries in some cases, therefore ensuring
their correct behaviour is essential. While testing has been for many years the
traditional way of validating the PLC control system logic, CERN developed a
model checking platform to go one step further and formally verify PLC logic.
This platform, called PLCverif, first released internally for CERN usage in
2019, is now available to anyone since September 2020 via an open source
licence. In this paper, we will first give an overview of the PLCverif platform
capabilities before focusing on the improvements done since 2019 such as the
larger support coverage of the Siemens PLC programming languages, the better
support of the C Bounded Model Checker backend (CBMC) and the process of
releasing PLCverif as an open-source software.
