During the last decade it has been shown that reconfigurable computing systems are able to compete with their non-reconfigurable counterparts in terms of performance, functional density or power dissipation. A couple of concept and prototyping studies have introduced the reconfigurability within general purpose microprocessor world. This paper introduces a prototyping environment for the design of simple reconfigurable microprocessors. The work differs from the previous approaches in the fact that a systematical way (concerning both hardware and software sides) to design, test and debug a class of reconfigurable computing cores instead of one particular application is discussed. First experiments with a simple 8 bit prototype have shown that the reconfiguration allows performance gains by a factor 2-28 for different applications. The study has discovered some directions for further architectural improvements.