CSI-RTOS is a real-time operating system that comprises CSI, microkernel, driver components and application layer middleware, and provides embedded developers with lightweight, highly portable, highly configurable uniform interface.

C-SKY Software Interface (CSI) specifies the software platform interfaces of C-SKY chip: abstract interface for microkernel, CPU hardware abstract interface and driver abstract interface; microkernel is user configurable and provide users with uniform CSI kernel API. So far, FreeRTOS and uCosIII have been ported to CSI , multi-thread management, thread scheduling, semaphore, mutex and message queue of inter-thread communication are supported; application layer middleware comprises necessary components for embedded development ,e.g,storage management, protocol stack and GUI.