catofstealth / icegdrom

An FPGA based GDROM emulator for the Sega Dreamcast

iceGDROM

This is an implementation of IDE and the "Sega Packet Interface" as used by the Dreamcast GD-ROM drive, using an iCE40 FPGA.

In addition to the IDE interface itself, and the accompanying CD-DA interface, the FPGA bitstream implements an RV32EMC-compatible CPU and an SD Card interface. Software running on the CPU responds to disc access commands from the Dreamcast by fetching data from disc images on an SD Card.

For more detailed information, please see the webpage.

This is free software (and hardware) licensed under the GNU General Public License version 3.

Hardware

The hardware is based on the Lattice iCE40-HX8K Breakout Board. In order to connect this board to the Dreamcast motherboard, a custom "riser board" with the appropriate connectors and some additional components is used. The design files for this can be found in the pcb/riser directory. The bill of materials can be found in the file pcb/riser/bom.txt. The pin headers with a J designation should be soldered to the Breakout Board (pins facing downwards).

The components CN4, R8, D1, and JP2 through JP4 are optional. They are a passthrough for a slave hard drive, and not used by the GD-ROM emulator.

For the hardware to be complete, the following additional things are needed:

• A USB-mini cable to connect CN6 to the Breakout Board. This is how the Breakout Board is powered when not attached to a host computer.
• An SD Card module, to connect to CN5.
• Rubber feet or similar to support the weight of the board in the corners not resting on CN1.

Required tools

To build the FPGA bitstream, the following tools are needed:

• Yosys 0.6
• arachne-pnr
• icestorm

To build the RISC-V software, the following tools are needed:

• riscv32-unknown-elf gcc 10.2.0
• riscv32-unknown-elf binutils 2.34.0

Building

Building is done by running GNU make. Running make at the top level will build everything, running it in a subdir will build that part. Note that building in fpga requires the rv32 stuff to be built first.

The file rv32/source/config.h can be modified to adapt to the polarity of the CD signal on the chosen SD Card module, or to enable debug traces on the serial port of the FTDI chip.

In order to flash the FPGA bitstream to the breakout board, run make flash.

Making image files

Building the project will also create a host tool in tools/obj/makegdimg which can create image files from either .gdi files (for GD-ROM images) or from .nrg or .cdi files (for MIL-CD and audio CD images). The image files should be named DISC0000.GI0, DISC0001.GI0 etc on the SD Card. To switch between images, extract and reinsert the SD Card.

Acknowledgements

• RISC-V softcore "VexRiscv" was developed by Charles Papon
• GD-ROM connector pinout was provided by OzOnE
• SD Card and FAT code based on sdfatlib by Bill Greiman
• DiscJuggler reader code based on CDIrip by DeXT/Lawrence Williams