Creating a testing process, certifying, and developing software for a railroad system of SIL4 (Security Integrity Level)

co-creation of architecture, design, code, and tests for the system

a system aligned with SIL4
in accordance with the EN 50128 standard

implementing the process
of test automation and selection of tools for static analysis and code coverage

co-creation of architecture, design, code, and tests for the system

a system aligned with SIL4 in accordance with the
EN 50128 standard

implementing the process of test automation and selection of tools for static analysis and code coverage

important information




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Voestalpine is an international capital group manufacturing, integrating, installing, and servicing devices and systems for improving efficiency and safety in railway and roadway transportation.


The client wanted to update their present HW-SW (hardware-software) product to expand to a new market. They were searching for a reliable partner to provide them with a complete set of development and testing services and support the process of certifying the product.

The partner had to be able to provide a complete service of developing safety-critical software for the purpose of railroad traffic. Due to the scale and level of innovation of the project, the support was to extend beyond just technical or procedural competences, but most importantly, finalizing the process by certifying the product and complementing it with thorough documentation. 


The software was to be produced for already existing hardware.


The system’s purpose was to control the occupancy of rail sections by detecting the passing trains and it was required to follow the CENELEC SIL-3 and SIL-4 standards.


We accepted this challenge. We used the client’s team’s extensive knowledge of the railroad industry and the potential for product development. We proved to be a reliable partner by delivering high-quality programming services based on modern hardware solutions.


Our complete support included two complex projects: one for development and one for testing.

Development involved extensive programming, architectural, and procedural support in designing, producing, and integrating the resulting firmware with the client’s HW platform.


Testing was all about preparing a multi-level testing process including unit tests, code review, static code analysis, integration tests, functional tests, and performance tests. The tests were to be performed, the entire process documented, and the system certified.

Project 1: software meeting the highest security standards


The project objectives:

· monitoring and occupancy control of railroad sections;

· controlling the safety of trains;

· integration with the client’s new HW platform;

· safety-critical software.


What we delivered:

· firmware meeting the requirements of SIL-4, the ISO50128, and ISO50159 standards;

· developing the code crucial for communication and security;


The effect of the project:

· developing embedded software – designing, expanding, and integrating with the railroad signaling system devices.

Project 2: software tests meeting the highest requirements of SIL-4 in railroad security.


The project objectives:

· designing the entire process of software testing;

· test execution;

· preparing testing result reports for the purpose of certification.


What we delivered:

· multi-level tests;

· a complex testing framework for the system;

· developing the architecture, code, testing strategy, test plan, test assumptions, and cases;

· test automation structure (testing bundles, intermediate code, and test cases);

· fully developed and documented test processes;

· defining and implementing code coverage and static analysis tools;

· test and development documentation schemes;

· implementing DOORS in the area of testing and development;

· well-organized testing and the reporting mechanism;

· the laboratory (mean power density of 200W/m2),

· technical documentation for testing procedures and test results. 


The effect of the project:

· multi-level testing and integration validation;

· successfull TÜV SÜD audits,

· supporting the system homologation process;

· implementing the new culture of developing software based on automatic testing;

· an efficient and reliable process of testing and defect reporting.


The product received the TÜV SÜD certification and the testing process was successfully verified and accepted by the proper certification body.

When our engineers relieved the client’s team of some of its workload it was able to focus on its other tasks. Our proposed solution: complementing the team with scalable resources provided on-demand, resulted in optimizing the cost of software development. 


Six months after launching the cooperation in creating the embedded system the client offered us to expand the project by three additional engineers to include software development and testing for an application for configuring the system. It was also crucial to provide support in certification – we represented the client in the TÜV SÜD certification for the testing process. We have continued to support the engineering team of Voestalpine since 2015.


During this cooperation, the software has passed certification and the system has been successfully introduced to the market. Voestalpine has operated with high-quality software aligned with the CENELEC SIL-3 and SIL-4 standards, meeting the highest functionality and security requirements for systems controlling railroad section occupancy.


“Solwit S.A. was responsible for the implementation of part of the embedded software for the system, in accordance with the rigors of the industry railway standards, and for ensuring the quality of the software in an automated test environment. Today, the UniAC (2) system is implemented by railway line operators all over the world, ensuring rail traffic safety in line with standards. Currently Solwit, as a permanent partner of Voestalpine SIGNALING, participates in the processes of further maintenance and development of the system, at the same time providing support in adapting the solution to the requirements of individual target markets.”

Przemysław Wołoszyk, Development Director, Voestalpine SIGNALING Sopot Sp. z o.o.


Railway industry standards: CENELEC SIL4 and ISO 50126, ISO 50128, ISO 50129, ISO 50159, redundancy, MISRA C 2012, UML modeling, PIC32 uC CAN family, SPI, Ethernet, EtherCAT


SVN, Redmine, Enterprise Architect, MPLAB X IDE, Pc-Lint, Cppcheck, Code collaborator, Gerrit, Vera++, Uncrustify, Jira, Redmine, Jenkins


C, C#, .NET, ASM, PIC32, ARM

CI environment

Jenkins, Unity, dedicated validation model, network equipment and embedded devices, plus elements of railway infrastructure.

Test documentation in accordance with IEEE 20119

Settlement model

Time & Materials