Contents

• Introduction
• Objectives
• Bus Architecture

Introduction.

The aim of this project is to produce a working free computer design along with a set of useful models and tools. The idea is that all the workings of the design are visible and open to understanding. The usefulness of the resulting computer is of secondary importance.

Each chip in the computer must be simple enough that a detailed model (rather than just a behavioural model) can be produced on the back of an envelope. This criterion is still a little subjective, but I think it gives the right idea. I want to rule out microprocessors and micro-controllers, but I want to include simple logic and RAM chips. The reason for this restriction is to ensure that the design is not obscured by the use of complex chips.

Objectives.

We want to produce the following items:

• A working computer.
• Diagrams and production data of all circuit boards.
• A description of how it works, in detail down to the gate level (without spelling out how a flip-flop works every time).
• Verilog models of all chips and circuits.
• A software model of the computer.
• A port of the GNU toolchain.
• A port of a suitable operating system.

The computer should support the following devices/interfaces (with host and slave support for interfaces where this makes sense):

• Non-volatile memory (for booting).
• High capacity memory (DRAM).
• Memory management unit.
• Parallel printer port (including advanced modes).
• PS/2 keyboard/mouse ports.
• Liquid Crystal Display.
• IDE interface.
• RS232 serial ports.
• A CPU.

This may take a while. :-)

Bus Architecture.

With so many peripherals, it makes sense to separate the work out into separate tasks which can be completed independently. To achieve this, I plan to have a backplane with plug-in cards. There will be a standard (although not too standard) interface between the backplane and the cards.