Projects — Retro-Active

FemtoRV Retro Co-Processor

A RISC-V co-processor for vintage computers — HDMI GPU, PS/2 keyboard, FM synth, SD card, all on a $15 FPGA.

6502 Bridge

A bridge from a stock 1 MHz MOS 6502 onto the Retro-Active common bus, in two flavours: 9 chips of pure 74-series, or 4 chips with a single 22V10 PAL/GAL. Both pass the same cocotb test suite.

68000 Bridge

A bridge from a 10 MHz Motorola 68000 (asynchronous bus, /AS + /DTACK handshake) onto the Retro-Active common bus, in two flavours: 12 chips of pure 74-series, or 6 chips with a single 22V10 PAL/GAL.

6502 Reference Main Board

A finished 6502-based main board: CPU, the 6502 bus bridge, ROM, RAM, a slot interrupt controller, and four backplane connectors on one PCB. The starter board for an 8-bit Retro-Active build.

68000 Reference Main Board

A finished 68000-based main board: CPU, the 68k bus bridge, RAM, ROM, IPL priority encoder, and four backplane connectors. The starter board for a 16-bit Retro-Active build.

Video Card

Reference video peripheral: HDMI digital output (and optional VGA), text and bitmap modes, character ROM and palette on the card. Drops into any Retro-Active backplane slot.

Audio Card

Reference audio peripheral: 4-voice 4-operator FM synthesis plus sampled PCM playback, mixed and emitted via I²S DAC. Drops into any Retro-Active backplane slot.

I/O Card

Reference I/O peripheral: SD card mass storage (FAT32), UART serial, and PS/2 keyboard. The 'console + storage' card for any Retro-Active build.

Bootloader

The boot ROM firmware that lives on every Retro-Active main board: probe storage, load the kernel, jump. Plus a serial monitor for when the kernel won't load.

Microkernel

The OS core: a small kernel that handles only scheduling, IPC, and memory. File systems, drivers, and shells run as user-space services. The same source compiles for 6502, 68000, 8086, RISC-V.

Single-User OS

DOS sensibilities, Unix CLI. One program at a time, FAT32 filesystem, a Bourne-style shell with pipes and redirection. Targets the 6502 and other tight machines.

Multi-User OS

Preemptive multitasking, multiple terminals, isolated user accounts. Same microkernel as the single-user OS, plus the services and policy a 'real' Unix-alike needs. 16/32-bit hosts only.

Driver Library

One C source per card type. Compiles against any host CPU through the appropriate GCC backend. The connective tissue that makes the card ecosystem actually portable.