SafeRTOS Usage Scenario #2

Single Microcontroller with Memory Protection Unit (MPU)

Using SafeRTOS on a single simple architecture microcontroller

Suitability

Medium criticality applications

Description

This usage scenario can be used in medium criticality applications when the certification body agrees that the proposed architecture and safety claims meet the standards necessary for the assessed system safety integrity level.

SafeRTOS manages the memory protection unit (MPU) to ensure tasks cannot inadvertently access each others RAM memory space, or the RAM memory space of the kernel. Further, SafeRTOS ensures that a task cannot inadvertently execute the kernel code.

Tasks execute in an unprivileged mode. The kernel executes in a privileged mode.

Why Use SafeRTOS in this Scenario?

In some cases, with careful system architecture consideration, this scenario allows source code written to different standards to execute in the same application (mixed criticality). This allows the amount of code that has to be written to the highest, most expensive, and most time consuming standard to be minimised. It also allows greater use of non safety critical bought in software - sometimes known as Software of Unknown Providence (or SOUP). The remaining software that does have to be written to the highest standard also benefits from decreased code size, easier testing, and better maintenance, for the same reasons documented in the Why Use SafeRTOS in this Scenario section on the Scenario #1 page.