Application-specific processors (ASIPs) look very promising as a platform for embedded systems since they comprise both the flexibility of a programmable device and the efficiency of application-specific hardware. A number of approaches to design an application-specific instruction sets were introduced during the last years. We apply the BURS (Bottom-Up Rewrite System) technique which is commonly used for retargetable code generation to this problem. As a result a simple algorithm is presented that generates both instruction set and assembly code from the source program; this algorithm can be used for retargetable code generation as well.