How to build a timely computing base using real-time Linux

We recently introduced a new model to deal with the problem of handling application timeliness requirements in environments with loose real-time guarantees. This model, called the timely computing base (TCB), is partially synchronised. From an engineering point of view it requires systems to be constructed with a small control part, a TCB module, to protect vital resources with respect to timeliness and to provide basic time related services to applications. Although many different instantiations of systems with a TCB can be envisaged we have chosen to implement a TCB using PC hardware running the real-time Linux operating system over a fast Ethernet network. The paper describes the experience gained during the implementation process and shows that it is possible to construct a TCB without the need for special software or hardware components. The problem of achieving real-time communication under RT-Linux is also discussed: we describe the porting of a Linux network driver to RT-Linux, explaining the required modifications to allow predictability.