The Lissom project deals with the hardware-software co-design methodology. In this project, an integrated desktop environment for a design of multiprocessor systems on chip was developed. This environment can be used also for developing applications for multiprocessor systems. One part of the environment is a debugger that can be used to debug single core systems. In this thesis, a single processor debugger tool is described in detail and an extension to this tool is proposed and implemented based on the Nexus standard. The extended debugger allows debugging of multiprocessor systems.