The wide range of applications and requirements and the increasing software size in communication systems encourage the use of high-level programming languages. For SPC telephone switching systems, CCITT recommends the language CHILL. One of the first public switching systems to use CHILL is EWSD, developed by Siemens for the world market. The hardware architecture of EWSD, being the basis for resolving the real-time requirements, is described as a two-level processing approach. The software is structured according to the concept of various layers and virtual machines. In order to support the development and test of CHILL software, a number of tools known as support software had to be developed.