About BoxLambda

BoxLambda is a hardware-software crossover project creating a homebrew, retro-style FPGA-based microcomputer. The goal is to create a sandbox environment for experimenting with software and FPGA gateware.

The Physical Setup

The physical setup.

Current Features

• Target FPGA: Arty-A7-100T.
• Ibex RISC-V core with machine timer and hardware interrupt support.
• Harvard architecture-based interconnect.
• Low-latency register and memory access across the SoC.
• Predictable instruction cycle counts.
• DFX Partial FPGA Reconfiguration support.
• DDR3 external memory access through the Litex memory controller.
• OpenOCD-based debug access on FPGA and Verilator.
• VERA-based VGA graphics: 2 layers, tile or bitmap mode, 2 banks of 64 sprites, 128KB Video RAM, 256 color palette.
• Dual YM2149 PSG Audio.
• SD Card Controller and FatFs File System.
• 24-pin GPIO, UART, SPI Flash Controller, I2C Controller.
• Real-time Clock and Calendar (RTCC) support.
• USB HID Keyboard and Mouse support.
• Picolibc-based standard C environment.
• Test application suite covering all SoC components, running on both FPGA and Verilator.
• Mecrisp Forth core + C FFI.

Gateware Block Diagram

Software Block Diagram

BoxLambda OS Architecture Block Diagram.

Key Goals

• Create a sandbox for experimenting with software and FPGA gateware:

  • It should be easy to jump in and do something: create, hack, tinker.
    • Simple Enough for One Person: A motivated individual can develop a solid understanding of the entire system, including software and hardware.
    • Deterministic Behavior: The duration of operations such as internal memory or register access must be predictable by design.
    • Self-Contained Run-Time Environment supporting high-level interactive and low-level systems programming.
  • Create a Modular Architecture allowing for a mix-and-match of software and hardware components. Optionally, support Partial FPGA Reconfiguration.

• Target Hardware: Digilent's Arty-A7.

• The computer supports the following peripherals:

  • USB HID Keyboard
  • USB HID Mouse (optional)
  • USB HID Joystick (optional)
  • Real-Time Clock and Calendar (optional)
  • Serial port
  • SD card storage
  • Flash Memory storage
  • VGA Display
  • Audio output

• Sound and graphics support retro-style 2D demos and gameplay.

Status (December 2025)

• Infrastructure (build system, etc.): Complete.
• Gateware: Complete and meeting requirements.
• Software: Early stage development. OS architecture defined. BoxLambda C Core partially completed. Mecrisp Forth Core partially completed. Mecrisp Forth Environment not started yet.

Links

• Source Code: https://github.com/epsilon537/boxlambda/
• Project Blog: https://epsilon537.github.io/boxlambda/
• Project Documentation: https://boxlambda.readthedocs.io/en/latest/