Minimig

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Minimig (short for "Mini Amiga") is an open source exact FPGA re-implementation of an Amiga 500.

Minimig started life in secrecy around January 2005 as a proof of concept type of deal by the 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 in FPGA and this was released under the open source license GPLv3 on the 25 July 2007.

Original prototype
The original Minimig prototype is based on the Xilinx Spartan-3 Starter Kit, the OCS chipset is synthesized in the FPGA. Two pcb boards are attached via the fpga kit expansion ports. The first one holds a 3.3V M68000 type CPU. The second has MMC memory card slot with the use of a small PIC microcontroller as acting disc controller that supports the FAT16 filesystem and does on-the-fly .ADF decoding.

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

The prototype was shown at an Amiga meet and loads most Amiga programs although bugs do exist. Coding is done in Verilog because Dennis found VHDL not to be his cup of tea. All done on a PC using Xilinx Webpack software.

Some users have suggested plans to make a joystick style direct-to-tv device for people wanting to play old Amiga games or run software. However a new single board version pcb has been designed, moving away from the Xilinx Starter kit.

Why

 * Run Amiga specific application software to convert files to newer platforms.
 * Run software only available on Amiga.
 * Games.
 * FPGA development experience using Verilog.
 * Creating something for the community.
 * Proof of Concept.
 * Can create new games to take advantages of the new features in Minimig (faster memory, more memory, sprites, colours, etc), while maintaining full compatibility with the classic Amiga.
 * Make the Amiga custom chip technology concept available under GPL.

Platform

 * Xilinx Spartan-3 400k gate (XC3S400-4PQ208C) FPGA using 60% capacity.
 * Freescale MC68SEC000 (MC68SEC000FU20; MC68SEC000AA20 proposed as replacement part by Freescale), 3,3V, running programable at 7.09379 and 14.18758 MHz. (However there's no 'E' clock, MOVE sr, is privileged and there is no real replacement instruction. This does not seem to affect any programs as of yet however.)
 * Amiga ChipRAM bus and FastRAM merged into a single synchronous bus running at 7.09379 MHz.
 * 2 MB 70 ns SRAM organised as 2 524288*16 banks.
 * MCU PIC 18LF252-I/SP (an alternative would be Atmel AVR) implements a FAT16 disclayout and handles loading of fpga configuration and kickstart. Simulates a floppy to the Amiga by encoding on the fly from .ADF files.
 * MMC Flash memory card to load fpga configuration, kickstart and software for the simulated computer.
 * 3 LEDs to display the system status - Main power (blue) - Amiga Power (red) - Drive activity (green).
 * Video D/A consists of 4 resistors for each color red, green, blue (4 bits/color) and output via VGA connector. Minimig schematics v1 Page3
 * Audio from an 8 bit dithering sigma-delta converter with 2nd order analogue filter.
 * +5V DC main power.

Ports

 * Spare 4x generic I/O from the fpga
 * JTAG for programming chips
 * RS232 serial port
 * 2x Joystick
 * HD15F VGA video
 * MMC Flash memory card slot.
 * PS/2 connector Keyboard + Mouse
 * 3,5 mm audio jack
 * +5V DC 2,1 mm cylindrical dc plug power supply inlet.

Implementation

 * OCS PAL video.
 * 512 kB SRAM RAM for Kickstart used as ROM.
 * 1 MB SRAM ChipRAM and 512 kB SRAM Ranger/SlowRAM.

Issues

 * Needs a binary copy of kickstart from a real Amiga 500 due that it's copyrighted.

Tools
Computer to compile the project:

Shuttle barebone, Prescott Pentium 4 3 GHz, 1 GiB Ram, Software Xilinx Webpack version 6.3.03i (2007-07-22 9.1). Time from source .bit configuration file = 2 minutes. Cache and memory speed is vital for fpga software.

related projects

 * Amiga floppy project