Can it run DOOM? This is an entry for the Hackaday Retrocomputing Challenge by DigiKey, brought up on the Intel Cyclone IV (Terasic DE0-Nano) FPGA, building on the previous CPU work
I put my dual-issue RV32IM superscalar CPU, with custom UART, I2C, and FIFO IPs, on an FPGA and built a retro system around it. A launcher lets you choose between DOOM, a Wolfenstein-style raycaster, and custom games such as Snake, 2048, Tetris, Minesweeper, and Flappy Bird. It also runs classic 8-bit software in a CP/M 2.2 environment and CHIP-8 games through a software interpreter
The CPU runs from SDRAM, with programs and game data loaded over UART through a CP2102 USB-to-TTL adapter. Keyboard input comes back over the same link into a hardware key register with press and release events. Each tick, the core reads the input, updates the running program, and writes an 8-bit framebuffer to SDRAM. On a frame commit, the core clock briefly pauses to burst the frame into a TX FIFO, streaming it over UART at 45 FPS to a host RGB viewer. A monochrome version is also displayed at ~33 FPS on an SSD1306 OLED over I2C
Before putting it on hardware, I built the same system in Verilator, running DOOM at 1.38 IPC while keeping the same MMIO interface and replacing SDRAM and peripherals with testbench stand-ins. A fast harness with snapshot/restore made iteration much easier, and a web bridge let me play it directly in the browser
Getting everything onto the board meant cutting predictor tables, making wide multiply/divide iterative while keeping the fast path on DSPs (holding ~1.35 IPC after the cuts), retuning the serial framing, and repacking the game assets to fit in SDRAM. CoreMark CRC checks caught functional issues before I started debugging the game itself
Alongside this, I’ve also been extending the same CPU toward a simple Out-of-Order design to explore the Tomasulo algorithm through an intuitive walkthrough
PS. Full write-ups (design decisions, debugging): https://mummanajagadeesh.github.io/categories/riscv/