UPDATE: Mikolas has added support for the DE2-70 board. Check his repo here: https://github.com/mikolas/socz80-de0_nano
Due to my intrinsic, chronic curiosity, for a long time I wanted to get a in touch with FPGA and related technologies (Verilog, VHDL, etc…), and experience the feeling of total control, having both hardware and software subdued to my control (well, not so much, due to the mysterious and semi-secret process of synthetization and fitting done by the tools involved in the process, but you get the idea).
So finally, some months ago, I bought a DE0-nano. This is a small but nicely built device, easily programmable with an integrated USB Blaster, and with a relatively low price (~70 €), which makes it perfect for learning and practicing a little.
After a few project of blinking LEDs and playing with clocks and PLLs, I’ve decided to take a step further and seek for a challenge. Then I came across the socz80 project, an amazingly cool project for building a Z80 compatible computer in FPGA-synthetizable VHDL. The code was targeted for the Papilo Pro board, which is a Xilinx based device (the FPGA world is divided between two major makers, Xilinx and Altera), so I decided to give a try and port it to the DE0-nano.
After a few hours dealing with timing problems, I managed to get it running. This is how I’ve done it.