an AVR based 8-bit Microcomputer
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README.markdown

DAN64, an AVR based 8-bit microcomputer

This is my personal attempt to build a 8-bit microcomputer based on the popular ATmega328 microcontroller (MCU) as an excuse to learn some electronics. Check docs/ directory for further information.

The microcomputer can be assembled and run in a breadboard with an Arduino Uno board.

General features:

  • Composite video black and white output, 256 x 192 resolution, 32 x 24 characters (8 x 8 pixels font, code page 437 character set).
  • PS/2 keyboard support.
  • 6502 virtual machine with system call interface to native code services.
  • Linear 64KB memory access from the virtual machine (256 bytes page zero, 256 bytes hardware stack, 6144 bytes of video RAM and 58880 bytes for user programs).
  • External storage support via audio in/out.
  • Integrated 6502 assembler and disassembler.
  • Basic shell supporting peek, poke, load, run, etc.

Project page: http://www.usebox.net/jjm/dan64/

General directory structure

  • docs/: documentation of the project, including schematics.
  • source code:
    • include/: general include files.
    • init/: main entry point for the firmware, including the implementation of the syscalls.
    • video/: composite video generation.
    • input/: PS/2 keyboard support.
    • memory/: memory functions.
    • vm/: 6502 virtual machine.
      • test/: virtual machine test suite.
    • storage/: storage using audio in/out.
      • tools/: wav audio file encoder.
    • dasm/: DAN64 assembler/disassembler.
      • tools/: standalone version.
    • tools/: some misc auxiliary tools (eg, font bitmap generation).
    • cc65/: CC65 runtime for cross-compiling C programs.
      • examples/: several user program examples in ca65 assembler and C.
    • images/: logos, pictures, screenshots, etc.

Build instructions

Install GCC AVR compiler and toolchain, and run make in the top level directory.

If avrdude is installed and you want to deploy to an Arduino Uno board you can try make upload, although some tweaking may be required (eg, the USB port).

The examples and the CC65 runtime require the CC65 compiler. If the binaries are in your path, just use make.

The user programs can be encoded into audio using the encode tool in the storage module (requires POSIX getopt and libsndfile).

Pandoc is required to build the documentation (although it is readable as it is in markdown format).

Notes

Video:

  • Timing is set for PAL.
  • Output is de-interlaced.
  • It may require set TV's AFC (Automatic Frequency Control) to "mode2" (usually for VCRs or Camcorders).

Input:

  • Supported UK PS/2 keyboard layout only, but is easy to adapt to other layouts.

Storage:

  • Audio in requires quite high volume, start with a 90% and adjust.
  • If you have problems loading DAN64 saved programs, try using a smaller value for R3 (eg. 320 instead of 1K).

Author and licensing

Juan J. Martinez jjm@usebox.net

This software is free software (see LICENSE file for details), unless explicitly stated otherwise.