Minimig

Minimig 120x120 mm PCB board (Nano-ITX size)[1]

Minimig (short for Mini Amiga) is an open source re-implementation of an Amiga 500 using a field-programmable gate array (FPGA).

Minimig started in secrecy around January 2005 as a proof of concept by Dutch electrical engineer Dennis van Weeren. He intended Minimig as the answer to the ongoing discussions within the Amiga community on implementing the Amiga custom chipset using an FPGA. The project's source code and schematics were released under version 3 of the GNU General Public Licence on 25 July 2007.

Original prototype

The original Minimig prototype is based on the Xilinx Spartan-3 Starter Kit, the Original Amiga Chipset is synthesized in the FPGA. Two printed circuit boards are attached via the FPGA kit expansion ports. The first one holds a 3.3V Motorola 68000 type CPU. The second has a MultiMediaCard slot with a small PIC microcontroller acting as a disc controller that supports the FAT16 filesystem and does on-the-fly Amiga disk file (ADF) decoding.

     VGA-+-PS2  (joystick etc.)
         |
CPU <-> FPGA <-> Microcontroller <-> Flashmemory
         |
        RAM

The prototype was shown[2] at an Amiga meet and loaded most Amiga programs although bugs did exist. Van Weeren's personal preferences led to the use of verilog instead of VHDL on a PC using Xilinx Webpack software for code development.

Purposes and intent

Hardware

Platform

As of Minimig rev1.0 board:

Ports

Implementation

Roadmap

Date Event
2005-03-06Verilog sources coding started.
2005-12-05Announcement of the project.
2006 SpringVerilog sources completed.
2006-06-11Screenshoot of schematic for board v1.0 published.
2006-10-15Schematic for board v1.0 completed.
2007-06-xxSources predicted to be released, but weren't.
2007-07-04Last source edit (core).
2007-07-13Busy making website for the project.
2007-07-24Minimig sources released on the official website.

Issues

Development tools used

Future

Upgrades

Read/write support

On 2008-09-03 a new FPGA core enables read/write support, as well as some Chipset improvements.[9]

ARM controller board upgrade

On 2008-12-22 a replacement board that fits in the PIC (MCU) controller socket were announced. It makes harddrive, 4x floppy disk and write support possible.[10] The FPGA core is the same for the new ARM and PIC firmware but only the ARM has enough resources to support four drives. The PIC only supports two. The upgrade also allows one to select to increase the CPU speed from 7.09 to 49.63 MHz with a 4 KB zero waitstate CPU cache. But it requires an FPGA core to actually carry it out (which works with the 16 MHz 68SEC000 chips).[11] The harddrive support is available by a virtual A600/A1200 style GAYLE parallel ATA interface. Up to 551 kByte/s[11] is possible with a minor hardware modification. Otherwise only ~300 kByte/s is possible.[12]

USB peripherals and MIDI

The Minimig port for the MiST board supports USB peripherals including USB mice, USB keyboards and USB mice as well as a physical MIDI interface.[13]

Additional 2 MB RAM

On 2008-12-22 a modification of the original PCB by piggybacking another set of SRAM chips enables up to 4 MiB of RAM in total.[10]

AGA support

The Minimig port for the MIST board has been updated to support major AGA features allowing it to run many AGA games. A binary release as well as the full source code is available under GPL.[14][15][16][17]

An unreleased Minimig core has been upgraded with AGA support and extended to support at least 50 MiB of Chip memory on the prototype Replay board designed by Mike Johnson at FPGA Arcade.[18][19][20]

Similar projects

Jeri Ellsworth, who made the C64 Direct-to-TV Commodore 64 on a chip ASIC, had a working Amiga on a chip prototype in 2003. Except for the 68000 processor and disk interface, everything was emulated inside a FPGA. However, the project was never finished or turned into an ASIC.[21]

Illuwatar, a small private hardware designer in Sweden, implemented a Mini-ITX form factor version of the Minimig under the Open Source design License. This hardware version fits in standard Mini-ITX cases and has dimensions of 17 cm x 17 cm. Connecting ports in this version were moved to the back of the mainboard to comply with Mini-ITX requirements.

On 9 Feb 2008 ACube Systems announced the availability of finished Minimig v1.1 boards.[22]

On 2006-10-11 Jens Schönfeld at Individual Computers revealed that they had been working on a commercial Amiga-in-FPGA for the past year called "Clone-A" that is similar to Minimig. In contrast to Minimig, Individual Computers's Clone-A was developed by a three-person development team employing a powerful logic analyzer. The system will use clone chips to replace CIAs, Paula, Gary, Agnus and Denise. The CPU will be the original from Motorola. Final chips will also include AGA and a working parallel port to enable 4-player games.[23] Still unreleased as of 2015.

Wolfgang Förster has completed the Suska project, which is an Atari ST-on-FPGA.

Inspired by Minimig Till Harbaum invented MIST, an open FPGA based implementation of Atari ST and Amiga intended to have a low price and be easy built at home. Different than Miniming, the 68000 CPU is not present as physical device but implemented inside the FPGA.

References

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