HCS12X series processor is a member of dual-core processor family with a coprocessor. Traditional single-core Operating System (OS) can't support the coprocessor. In order to take full advantage of the performance of the processor, a real-time operating system named AutoOSEK-CP is designed on the basis of AutoOSEK, which is a single-core operating system based on OSEK/VDX. To support dual-core processor, a new architecture was presented in AutoOSEK-CP. In this new architecture, alarm management, interrupt processing and inter-core communication mechanism are designed and implemented.