# M8SBC-486

**Repository Path**: jiangkaiwen/M8SBC-486

## Basic Information

- **Project Name**: M8SBC-486
- **Description**: All the sources (Schematics, PCB, VHDL, BIOS sources) for the M8SBC-486. This project is a 486 Homebrew computer, with some efforts to make it kinda PC compatible
- **Primary Language**: Unknown
- **License**: Not specified
- **Default Branch**: main
- **Homepage**: https://theretroweb.com/motherboards/s/maniek86-m8sbc-486
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2026-01-27
- **Last Updated**: 2026-01-27

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# M8SBC-486

All the sources (Schematics, PCB, VHDL, BIOS sources) for the M8SBC-486. 

This project is a 486 Homebrew computer, with some efforts to make it kinda PC compatible. See [my page about it](https://maniek86.xyz/projects/m8sbc_486.php).

<img title="" src="photos/IMG_20251019_031401_g.jpeg" alt="soldered board">

## Specs:

- 150*150mm 4 layer PCB
- PGA-168 socket for 5V 486 CPUs.
- Xilinx Spartan II XC2S100 FPGA as "chipset". Codename "Hamster 1"
- 4MB SRAM, (8*HM628512)
- 256KB of ROM (W29C020) (224 KB accessible)
- 8254 Programmable Interval Timer
- 8259 Programmable Interrupt controller
- Two 16-bit ISA slots
- PS/2 Keyboard port. Controller is implemented in the FPGA
- Simple CMOS RTC and CMOS storage. Implemented in the FPGA too
- ATMega128 as reset circuit handler, nonvolatile CMOS storage and bitstream loader.

The FSB frequency is currently set to a fixed 24 MHz (DX2 CPUs run then at 48 MHz), but this can be changed by uncommenting/commenting lines in the FPGA source.

Secondary PIC and DMA are missing, so the compatibility is not full. The missing DMA especially breaks support for sound cards.

## Current progress:

The hardware and FPGA are mostly done. BIOS is capable of booting DOS. There are a few issues & bugs, but they are being slowly fixed.

Among the most impressive things the board (as time of writing: 09/01/2025) is capable of: 

- Booting Linux (2.2.26) (using custom bootloader, release TODO)

- Booting MS-DOS and FreeDOS: The software compatibility is mixed. Some software hangs the system, throws exceptions, but some run fine. Most notable are: Second Reality demo (no sound, small glitches at two parts), Prince of Persia, Fasttracker II (PC speaker works in one mode, LPT DAC works okay), 3DBench 1.0c, CACHECHK.

- Running DOOM ([FastDOOM](https://github.com/viti95/FastDoom) running on FreeDOS 1.4)

## Hardware diagram

<img src="photos/hw_diagram.png" alt="Hardware diagram">

<hr>

## Special thanks to [PCBWay](https://www.pcbway.com)!

[<img title="" src="photos/pcbway.png" alt="" width="400">](https://www.pcbway.com)

Special thanks to PCBWay for sponsoring PCBs for this project! Their sponsorship was a huge help and enabled me to make progress with this project. PCBWay is a well-known PCB prototyping and manufacturing service, providing high-quality boards and excellent customer support. I have worked with their boards in the past and can say that they are of great quality. I easily placed an order for PCBs on their platform for this project without any problems. The sponsorship also included a free quick delivery option. If you’re looking for reliable PCB prototyping and manufacturing services, I highly recommend [checking them](https://www.pcbway.com).

# Folders

## pcb/

Schematic and PCB design for this homebrew computer. Board is 150mm*150mm with 4 layers. (Placement of the screw holes is not compliant with any standard)

## chipset/

Sources for the "Hamster 1" chipset. FPGA used is XC2S100 (Xilinx Spartan II). Compile with Xilinx ISE 10.1

## avr/

Sources for AVR ATMega128:

Small AVR firmware that configures the FPGA from on-chip flash at power-up and manages system reset for the M8SBC-486 project

## bios/

M8SBC-486 SeaPig BIOS

Based on this project: [b-dmitry1/BIOS](https://github.com/b-dmitry1/BIOS)

## Disclaimer

This project is essentially my hobby, as I like retro, electronics, digital circuits and low-level programming. I never expected this computer to run DOS in the first place. I consider it pretty much experimental and made to research the workings of older x86 chips. I am pretty sure that this work could be used to build something more robust and stable or even to develop fully custom-made boards for other x86 CPUs. It took me a lot of time, but I don't regret it. There are still many issues, but it's heartwarming that I can get so much existing software to work. And, thanks to everyone for support!

## Acknowledgements

Special thanks to: TheRetroWeb community, [b-dmitry1](https://github.com/b-dmitry1) and [PCBWay](https://pcbway.com/)

## More images

<img alt="PCB bottom" src="photos/IMG_20251002_235903_preview.jpeg">
<img width="600" alt="3d render back" src="photos/render_back.jpg" />
<img width="600" alt="pcb view" src="photos/pcb_view.jpg" />