Developing an entire monolithic automotive operating system and complex trajectory planner to full ASIL-D standards is economically and technically prohibitive: every line of code requires formal unit testing with 100% Modified Condition/Decision Coverage (MC/DC), exhaustive static analysis, and rigorous tool qualification. ASIL decomposition allows developers to isolate the high-risk hazards into a small, provable safety monitor.
In the classic Doer-Checker pattern, the 'Doer' is an advanced, high-performance algorithm running on a Linux or QNX core calculating complex vehicle kinematics. It is developed to ASIL-B standards. The 'Checker' is a deterministic, lightweight safety envelope monitor running on an isolated lockstep Cortex-R52 core, also developed to ASIL-B. If the Doer commands a steering angle that violates physical friction limits, the Checker overrides the command and pulls the brakes within 5 milliseconds.