The musical CPU

A typical student project in a digital system design or a computer organization course is the design of a CPU for a small, simplified instruction set. However, it can be a challenge to devise such projects in a way that simultaneously reinforces effective logic design principles, is hands-on, can be completed using inexpensive and standard laboratory equipment, and (most importantly) inspires, as part of the design process, both imagination and creativity in students. This paper describes such a project where the target instruction set is designed to implement (i.e. "program") music and play songs on commonly available FPGA hardware. The "musical CPU" uses three carefully designed instruction formats to literally describe the sounds and flow of music by mapping various constructs of music (notes, tempo, etc.) into corresponding specially designed assembly language instructions that encode the desired musical effect; hence, the emphasis is on the creative nature of the design process, something all computing and engineering educators strive for in the development of good classroom projects. The details of this project necessitate consideration of many cross-cutting issues in computer science and engineering including instruction set design, finite state machine control design, programming logic, and user interaction issues.