Single-Core processors and controllers have been the de-facto standard for aviation software since the early beginnings when computers were utilized in flight systems. This is primarily due to their simple design and determinism of execution. At first glance, it seems comprehensible that a flight computer that takes control over a critical safety system should be dedicated to that task only. Certification authorities, such as the European Union Aviation Safety Agency (EASA) and the Federal Aviation Administration (FAA), have substantiated that point of view by not allowing to certify flight systems that support more than one active processor core (RTCA/DO-254, Design Assurance Guidance for Airborne Electronic Hardware, published by RTCA Incorporated. The European denomination is EUROCAE ED-80).
Interested in technical stuff regarding the implementation of the demands of CAST-32A? Check out https://www.sysgo.com/services/knowledge-center/cast-32a-positioning-paper!