Single Microcontroller with Memory Protection Unit (MPU)
Medium criticality applications
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
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.