In my bachelor studies, I and four other students built a RISC-based microprocessor architecture. This involved a thorough design of the processor’s components, layout, instruction set, and memory management from the ground up, which we implemented in VHDL. We also developed mnemonics and an assembler to assemble the code according to our instruction set. We then wrote programs that process inputs such as button presses and switches, and output via a set of LEDs.
Here, you can learn more about this project: RISC Microprocessor