FMU-proxy: A Framework for Distributed Access to Functional Mock-up Units

Abstract

The main goal of the Functional Mock-up Interface (FMI) standard is to allow simulation models to be shared across tools. To accomplish this, FMI relies on a combination of XML-files and compiled C-code packaged in a zip archive. This archive is called an Functional Mock-up Unit (FMU) and uses the extension .fmu. In theory, an FMU can support multiple platforms, however this is not always the case and depends on the type of binaries the exporting tool was able to provide. Furthermore, a library providing FMI support may not be available in a particular language, and/or it may not support the whole standard. Another issue is related to the protection of Intellectual Property (IP). While an FMU is free to only provide the C-code in binary form, other resources shipped with the FMU may be unprotected. In order to overcome these challenges, this paper presents FMU-proxy, an open-source framework for accessing FMUs across languages and platforms. This is done by wrapping one or more FMUs behind a server program supporting multiple language independent Remote Procedure Call (RPC) technologies over several network protocols. Currently, Apache Thrift (TCP/IP, HTTP), gRPC (HTTP/2) and JSON-RPC (HTTP, WebSockets, TPC/IP, ZeroMQ) are supported. Together, they allow FMUs to be invoked from virtually any language on any platform. As users don’t have direct access to the FMU or the resources within it, IP is more effectively protected.