OSEK/VDX (Open Systems and their Interfaces for the Electronics in Motor Vehicles/Vehicle Distributed eXecutive) is an open platform that has produced specifications for an operating system, a communication and a network management for automotive embedded systems to enhance software portability and reusability. Generic Embedded System developed by DGIST provides an environment to develop an automotive embedded software easily. In this paper, we introduce the Generic Embedded System and OSEK Development Tools and present a detailed case study to describe an example of OSEK-based automotive software application of RCS (Roomlamp Control System). Automotive engineers can learn easily OSEK OS application software and utilize this case study to other application software development through this case study.