The last fifteen years have witnessed a resurgence of interest in asynchronous digital design techniques as they promise to liberate VLSI systems from clock skew problems, offer the potential for low power and high performance and encourage a modular design philosophy which makes incremental technological migration a much easier task. This activity has revealed a need for modelling and simulation techniques suitable for the asynchronous design style. The concurrent process algebra Communication Sequential Processes (CSP) is increasingly advocated as particularly suitable for this purpose. This paper discusses the modelling of SAMIPS, a synthesisable asynchronous MIPS processor core, in Balsa, a CSP-based, asynchronous hardware description language and synthesis tool.