This is a compact open-source FPGA game console targetting the Lattice iCE40 UltraPlus series. It's being developed using the open-source yosys and nextpnr tools and can be run on both the iCEBreaker** and ULX3S* boards.
As a retro-inspired console, it does not use framebuffers, rasterizers, shaders etc. It uses character maps, sprites and raster effects to implement various effects. This allows it to render 480p scenes from 64KByte.
*: Only the ECP5-45F and 85F have the 128kbyte of block RAM required. It's been confirmed working on boards with Winbond flash but thought to work on others too. Potentially boards with a 25F can be supported by moving the CPU RAM to external memory.
**: iCEBreaker requires the additional 12bpp HDMI PMOD for video output. On the ULX3S, the onboard GPDI port is used for video output.
Platformer game hosted here.
Demo with placeholder assets just for illustration. This along with other similarly copyrighted assets are not published here.
- RISC-V CPU (configurable with VexRiscV or PicoRV32)
- Custom VDP for smooth-scrolling layers and sprites
- Custom "copper" coprocessor integrated into VDP to perform raster effects
- Custom multichannel ADPCM decoder / mixer (44.1KHz, 16bit stereo)
- Configurable video modes of 640x480@60hz or 848x480@60hz
- 4bpp graphics assembled from 8x8 tiles
- ARGB16 colors arranged into 16 palettes of 16 colors each
- Optional alpha blending using 4bit alpha intensity**
- 3x or 4x scrolling layers up to 1024x512 pixels each*
- 1x 1024x1024 pixel affine-transformable layer*
- 256x sprites of up to 16x16 pixels each
- 1060+ sprite pixels per line depending on clock and video mode
- 64kbyte of CPU RAM (2x iCE40 SPRAM)
- 64kbyte VDP RAM (2x iCE40 SPRAM)
- (S)NES-compatible pad interface***
The system doesn't require any RAM beyond what is available in the iCE40 UP5K.
*: Only one of these layer types can be enabled at any given time but they can be toggled multiple times in a frame using raster-timed updates. The 4x layer implementation is still included in this repo but was disabled due to VRAM usage constraints.
**: Visual artefacts can been seen if more than one alpha-enabled layer intersects with another i.e. using overlapping sprites.
***: PCB push buttons are used by default. although an original SNES gamepad can be used.
- yosys
- nextpnr (-ice40 for iCEBreaker, -ecp5 for ULX3S)
- icetools (if building for iCEBreaker)
- GNU RISC-V toolchain (newlib)
- fujprog (if flashing to ULX3S)
While the RISC-V toolchain can be built from source, the PicoRV32 repo includes a Makefile with convenient build-and-install targets. This project only uses the RV32I ISA. Those with case-insensitive file systems will likely have issues building the toolchain from source. If so, binaries of the toolchain for various platforms are available here.
The open-tool-forge fpga-toolchain project also provides nightly builds of most of these tools.
cd hardware
make icebreaker_prog
cd hardware
make ulx3s_prog
Demo software is included under /software and can be programmed separately. For example, to build and program the sprites demo:
cd software/sprites/
make icebreaker_prog
cd software/sprites/
make ulx3s_prog
A simulator using SDL2 and its documentation is included in the /simulator directory.
Demo software and simulator screenshots are included in the /software directory.
One of two RISC-V implementations can be selected. The implementation is chosen using the boolean USE_VEXRISCV parameter in the ics32 module.
- PicoRV32: Enabled when
USE_VEXRISCV=0. This was the original choice and the rest of the system was designed around its shared bus interface. While it is not as compact as the Vex, it is much faster to run in simulators as it is fully synchronous. - VexRiscV (default): Enabled when
USE_VEXRISCV=1. This was a later addition. A wrapper module is used to bridge between the Vex split IBus/DBus and the Pico-compatible shared bus. It is the more compact CPU which is especially important considering the size of the up5k target.
One of two video modes can be selected and only when the project is built. The video modes can't be toggled in software. The VIDEO_MODE variable in /hardware/Makefile selects which video mode to use. This Makefile variable in turn determines the value of the ENABLE_WIDESCREEN parameter in the ics32 module.
- 640x480@60hz: 25.175MHz VDP/CPU clock
- 848x480@60hz: 33.75MHz VDP clock, 16.88MHz CPU clock
Note the 848x480 video has two clock domains because the up5k cannot run the CPU at 33.75MHz and meet timing. The dual clock domain setup is automatically enabled when ENABLE_WIDESCREEN is set. The FORCE_FAST_CPU parameter is also available to force the single clock domain setup which fails timing in the 848x480 case, although the author hasn't seen it break even with substantial overclock.
The GAMEPAD_PMOD parameter enabels audio output on a to-be-released PMOD. This is untested.
Audio is output through the headphone jack in both analog / digital form:
- Analog output direct to headphones (noisy)
- Digital SPDIF using a 3.5mm -> RCA cable. The "composite video" cable can be plugged into the coax-in of an SPDIF receiver.
The assumed controller layout matches an original SNES gamepad.
By default, the controller is implemented using push buttons on the PCBs. Both the ULX3S and iCEBreaker buttons (on break out board) can be used but inputs are limited.
The GAMEPAD_PMOD parameter in the top level module can be set to use the gamepad / audio PMOD rather than the 3 buttons on the breakout board. Note this hasn't been fully tested yet.
The ENABLE_USB_GAMEPAD parameter in the top level module can be used to optional enable a USB gamepad on port US2. HID report descriptors aren't parsed so a fixed layout is assumed. More gamepads can be added over time since the only addition needed is a HID report decoder.
- A better README file!
- Many bits of cleanup and optimization
- Support for more USB gamepads
- Confirmed working support for original SNES gamepad (using PMOD)
- Confirm ULX3S boards with ISSI flash work as expected