Real-Time Operating System (RTOS) is an important tool in embedded artificial intelligence and IoT terminals. RTOS developed by different institutions has slight differences in real-time properties, scheduling rules, and communication mechanisms between tasks, but the basic elements are the same. This work is based on the general embedded computer(GEC) architectures, studies the RTOS resident method in BIOS and the remapping mechanism of external interface function. Taking the KL36 chip of NXP as an example, the resident implementation of mbedOS in the BIOS is given, and living example of external interface function remapping is given. Practice shows that the RTOS resides in the BIOS, which can shorten the compilation and linking time. At the same time, by remapping external interface functions, the understanding of the RTOS scheduling mechanism is simplified, the programming difficulty is reduced, and the technical basis is provided for effectively implementing the portability of applications under different RTOS.