Processes running under an operating system are independent and autonomous entities. However, they need to share resources, communicate, use OS services, etc. The operating system's services can be reached through system calls, which contribute - sometimes excessive - overhead activity. In some cases the payload activity, used in the system call, is much shorter than that needed for implementing the Exceptional Control Flow, implementing the system call frame. In certain cases, the OS service in question can be implemented in an alternative way, practically without overhead. The paper presents such a case, using an easy to understand simple example, an alternative implementation of a simple binary semaphore. The semaphore has been implemented and tested in a prototyping environment, using an operating system running on a soft processor equipped with custom instruction. For implementing the semaphores, a reconfigurable device was used.