The Ant64S - the Starter Edition

FPGA graphics. RISC-V power. No black boxes.

Ant64S is a modern home computer built the way classic machines were — with a fast CPU, custom graphics hardware, and direct access to the metal.

It combines a RISC-V processor with FPGA-based graphics and audio, using deterministic, memory-mapped hardware instead of drivers and shaders.

The result is a system that’s ideal for games, demos, tools, and creative software — including hardware-accelerated ImGui — and scales cleanly to the more powerful Ant64...

Core Philosophy

The Ant64S is designed around four core ideas:

• Deterministic hardware

  Graphics and audio are implemented in FPGA logic, not drivers or shaders. Software writes to memory-mapped hardware and gets predictable, cycle-stable behaviour.

• Modern CPU, classic programming model

  The 256MB SG2002 RISC-V CPU is fast and cached, but it interacts with hardware using classic memory-mapped I/O and command lists — closer to an Amiga or Atari ST than a PC GPU.

• Low overhead graphics

  Instead of a 3D GPU, the Ant64S uses a layer-based graphics system with:

• tilemaps
• sprites
• vector primitives
• a command list layer capable of rendering ImGui draw lists directly
• Creative-first design

  Like the C64, Atari ST, and Amiga before it, the Ant64S is designed to be:

• programmed directly
• explored by demo coders
• used by musicians and artists, not just gamers

CPU and Supervisor

Main CPU: SG2002 (RISC-V)

• Runs the OS, applications, simulation CPU cores, tools
• Treats the FPGA as a memory-mapped device over a QSPI bus

Supervisor MCU: RP2350

• Handles all “messy” external I/O:
• keyboard
• mouse
• USB MIDI
• USB joypads/controllers
• Presents clean, OS-friendly input data to the SG2000
• Offloads USB and real-time I/O complexity from the main CPU

This mirrors classic designs where a main CPU was supported by intelligent peripherals.

FPGA (Ant64S)

The FPGA in the Ant64S is from the same family as the other Ant64’s FPGA, but smaller. It provides:

Graphics subsystem

• A layer list defining active layers on screen
• Each layer has:
• a type
• mouse
• a memory pointer
• format and configuration
• Supported layer types include:
• bitmap / colour layers (32-bit friendly)
• tilemap layers
• sprite layers
• command list layer (used for ImGui and vector-style drawing)

The command list layer executes a stream of compact commands (32-bit words) that describe what to draw, rather than raw pixels — very similar in spirit to Amiga copper lists or early display lists.

Memory model

• Uses 32-bit memory widths (embedded PSRAM in the FPGA)
• No 36-bit memory on Ant64S
• All Ant64S layer formats and command structures are defined so they also work on Ant64

Anything that is not supported by the Ant64S is explicitly marked in Ant64S documentation as: Reserved, must be zero

Graphics Command Layer (Key Feature)

One of the most important features of Ant64S is the command list graphics layer, which allows:

• Direct rendering of ImGui draw lists
• Hardware scissoring (clip rects)
• Texture binding
• Indexed triangle drawing
• State persistence between commands

This makes it possible to build:

• modern UIs
• debug overlays
• editors
• tools

…without needing a full GPU or driver stack.

This command layer is intentionally designed as a strict subset of the main Ant64 command layer, so software written for Ant64S can run unchanged on the other members of the Ant64 family.

Software Model

From the SG2002’s point of view:

• The FPGA appears as a memory-mapped device
• Graphics, audio, and control registers are accessed directly
• No kernel drivers are required for basic graphics output
• Command lists are written to memory and executed by hardware

This keeps latency low and encourages experimentation.

What the Ant64S is not

• Not a PC
• Not a console
• Not a Linux SBC with a GPU
• Not just an emulator box

Instead, it is best thought of as:

A modern “home computer” architecture, designed for creativity, hacking, and exploration, using today’s silicon but yesterday’s clarity.

Relationship to the other members of the Ant64 family

• All Ant64 family members share:
• the same CPU family (SG2002)
• the same command list concepts
• compatible layer formats
• more layers
• more memory types
• higher colour precision
• more advanced audio/graphics features

Code written for Ant64S is intended to scale naturally to the other Ant64 family members.