HW/SW co-design of RSA on 8051

In this paper we present a project based approach to understand hardware-software co-design. The goal of the course ”Digital Platforms” is to teach the students, given an embedded application, which are the different options for implementation. Real world problems, especially in embedded systems, often require a design, which combines hardware for performance with software for flexibility. Contrary to this need universities often teach solely hardware design and software design. Between the two extremes, ASIC design and pure SW on a general purpose CPU, there are many different target platforms. To show that there are alternatives, in the design project associated with the class, a HW/SW co-design project is undertaken. The sample application for this project is a basic public key (RSA, El Gamal) application. This application is very attractive because due to the complex arithmetic and the large word lengths, it runs poorly on an embedded micro-controller. Yet, a pure ASIC application is also not a solution because it lacks flexibility to support multiple public key applications. Thus one of the requirements of the project is trade-off between flexibility and efficiency. The course addresses basic skills in hardware design, embedded software design, presentation skills, team work and design creativity. The final step requires adequate partitioning of hardware and software, designing an interface protocol and implementing and testing of the complete system. As there is no single point solution the students have to motivate their individual decisions and designs in written and oral form. The final grade is depending on the performance as well as on the originality of the design, and the argumentation in the report and the presentation.