Implementing the Bus Protocol of a Microprocessor in a Software-Defined Computer

Abstract

The paper describes a concept of a software-defined computer implemented using a classic 8-bit microprocessor and a modern microcontroller with ARM Cortex-M core for didactic and experimental purposes. Crucial to this design is the timing analysis and implementation of microprocessor’s bus protocol using hardware and software resources of the microcontroller. The device described in the paper, SDC_One, is a proof-of-concept design, successfully demonstrating the software-defined computer idea and showing the possibility of implementing time-critical logic functions using a microcontroller. The project is also a complex exercise in real-time embedded system design, pushing the microcontroller to its operational limits by exploiting advanced capabilities of selected hardware peripherals and carefully crafted firmware. To achieve the required response times, the project uses advanced capabilities of microcontroller peripherals – timers and DMA controller. Event response times achieved with the microcontroller operating at 80 MHz clock frequency are below 200 ns and the interrupt frequency during the computer’s operation exceeds 500 kHz.