This paper describes a distributed development environment, CAPS (Computer-Aided Prototyping System), to support rapid prototyping and automatic generation of source code based on designer specifications in an evolutionary software development process. The CAPS system uses a fifth-generation prototyping language to model the communication structure, timing constraints, I/O control, and data buffering that comprise the requirements for an embedded software system. The language supports the specification of hard real-time systems with reusable components from domain specific component libraries. CAPS have been used successfully as a research tool in prototyping large real-time control systems (e.g. the command-and-control station, cruise missile flight control system, missile defense systems) and demonstrated its capability to support the development of large complex embedded software.