The pre-certified Flexible Safety RTOS

A real-time operating system (RTOS) provides services, which helps to manage the continuously rising complexity of software development in embedded systems. In comparison to an operating system (OS) like Linux or Windows, the RTOS provides:

Note: When discussing the fundamental properties of a real-time operating system, it is not about super fast timings (of course, they are super fast) - more important is the guarantee and determinism of achieving the timing deadlines.

The following figure visualizes the term "deadline", often used in relation with real-time systems:

You see a task (in blue) which is starting to work with potential operations (read inputs, generate reaction and write outputs) on a system event. The timing deadline is the maximum allowed time until the task produces a system reaction.

When using a real-time operating system in a safety system, we need to ensure the correct function. The way and depth for proving of the functional behavior depend on the target market of the safety system. Each primary market has definitions and rules for the way to prove the correct behavior, written in standards:

We call the activities, required to pass the independent safety assessment for a specific standard: the certification. When performing these activities out of the context of a real safety system, we call the resulting component: a pre-certified component.

For the required depth for proving the functional behavior, the standards define safety capability levels with different names. The levels are derived from the occurrence probability of potential risks and the severity when happening:

Unfortunately, there is no simple mapping of safety capabilities from one market to another. The figure above shows a rough overview, based on the failure rate per hour. Some additional factors are important to consider (e.g., controllability, definitions of severity or risk acceptability frontier)