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Minimig started 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.
The prototype was shown[2] at an Amiga meet and loaded most Amiga programs, with some bugs. This prototype used verilog instead of VHDL on a PC using Xilinx Webpack software for code development.
Hardware
Platform
As of Minimig rev1.0 board:
Xilinx Spartan-3 400k gate (XC3S400-4PQ208C) FPGA using 82% capacity.
Freescale MC68SEC000, 3.3V, at 7.09379 MHz. However, there's no 'E' clock, MOVE sr,<EA> is privileged and there is no real replacement instruction.
Amiga Chip RAM bus and Slow RAM merged into a single synchronous bus running at 7.09379 MHz.
2 MB 70 ns asynchronous SRAM organised as 2x 524 288 x 16-bit banks.
MCUPIC 18LF252-I/SP[3] (An alternative is Atmel AVR) implements a FAT16 disk layout and handles loading of FPGA configuration and Kickstart. This simulates a floppy disk to the Amiga by encoding on the fly from ADF files.
3× LEDs to display the disk activity, main power, and Amiga power-up status. Amiga power-up status led will also change intensity to show audio filter status.
Video D/A consists of 4 resistors for each color red, green, blue (4 bits/color), and output via VGA connector.[4]
Audio from an 8 bit dithering sigma-delta converter with 2nd order analogue filter.
Software: XilinxWebpack version 6.3.03i (2007-07-22 9.1). Time from HDL source to loadable configuration file (.bit) = 2 minutes.CPU cache and memory speed is vital for the Synthesis + Place & Route Silicon compiler in FPGA generation software.
Future
Possible future developments include:
A faster CPU, ECS chipset, AGA graphics (new FPGA board is required), hard disk, ethernet, small RISC-Core for enhanced AROS functions, etc.
Use of a free kickstart replacement (e.g. AROS).[8]
A networked version would eliminate the need for swapping flash memories.
Upgrades
Read/write support
On 3 September 2008, a new FPGA core enables read/write support, as well as some chipset improvements.[9]
ARM controller board upgrade
On 22 December 2008, a replacement board that fits in the PIC (MCU) controller socket were announced. It makes hard drive, 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 an increase of the CPU speed from 7.09 to 49.63 MHz with a 4 KB zero wait state CPU cache. However, it requires an FPGA core to actually carry it out (which works with the 16 MHz 68SEC000 chips).[11]
The hard drive support is available by a virtual A600/A1200 style GAYLEparallel ATA interface. Up to 551 KB/s[11] is possible with a minor hardware modification. Otherwise only ~300 KB/s is possible.[12]
USB peripherals and MIDI
The Minimig port for the MiST board supports USB peripherals including USB keyboard and USB mouse as well as a physical MIDI interface.[13]
Additional 2 MB RAM
On 22 December 2008, 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 was 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 designed the C64 Direct-to-TVCommodore 64 on a chipASIC, 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.[22] 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.[23]
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 intends to use clone chips to replace CIAs, Paula, Gary, Agnus and Denise, and the CPU will be the original from Motorola. Final chips will also include AGA and a working parallel port to enable 4-player games.[24] Still unreleased since 2015.
Wolfgang Förster has completed the Suska project, which is an Atari ST-on-FPGA.[25]
Inspired by Minimig, Till Harbaum invented MIST,[26] an open FPGA based implementation of Atari ST and Amiga intended to have a low price and be easy built at home. Different than Minimig, the 68000 CPU is not present as physical device but implemented inside the FPGA.
Inspired by MIST, Alexey Melnikov invented MiSTer,[27] an FPGA based implementation of Atari ST and Amiga, based on a commercial board by Terasic : DE10-nano. There are at least five so-called "daughter boards" that enhance the capabilities of MiSTer.
Vampire V4 Standalone, released by Apollo Team in 2019, provides ECS/AGA chipset re-implementation, plus 68080 CPU and SAGA core, also using a field-programmable gate array (FPGA)[citation needed].
