danodus/graphite

FPGA based system with 2D/3D graphics acceleration

Graphite

Graphite is a FPGA based open source system with 2D/3D graphics acceleration.

Documentation

The documentation is available here: https://danodus.github.io/graphite/

Features

The system has the following features:

• RISC-V (RV32I + Graphite extension)
• UART (2000000-N-8-1)
• SDRAM (32MiB shared between CPU and video)
• Set associative cache (4-way with LRU replacement policy)
• VGA (60 Hz), 480p (60Hz), 720p (60Hz) or 1080p (30Hz) HDMI video output with framebuffer (RGB565)
• 2D/3D graphics accelerator (textured triangles)
• PS/2 keyboard
• PS/2 mouse
• SD Card with hardware SPI

Requirements

• OSS CAD Suite (https://github.com/YosysHQ/oss-cad-suite-build) (*)
• xPack RISC-V Embedded GCC (https://github.com/xpack-dev-tools/riscv-none-elf-gcc-xpack/releases) (*)
• Python3 with the following PIP3 packages installed: pyserial
• picocom
• SDL2 (for simulation only)

(*) Extract and add the bin directory to the path.

Note: Tested with oss-cad-suite-darwin-arm64-20240515 and xpack-riscv-none-elf-gcc-13.2.0-2-darwin-arm64.

Getting Started on ULX3S

cd soc/src/bios
make
cd ../../rtl/ulx3s
make clean;make VIDEO=<video mode> CPU_SPEED=<cpu speed> prog
cd ../../src/examples/test_graphite
make run SERIAL=<serial device>
picocom -b 2000000 <serial device>

and press 'h' for help.

The following video modes are available:

Video Mode	Description
vga (default)	640x480 60Hz
480p	848x480 60Hz
720p	1280x720 60Hz
1080p	1920x1080 30Hz

The following CPU speeds are available:

CPU Speed	Description
slow (default)	40MHz
fast	50MHz

System Simulation

cd soc/src/examples/test_video
make
cd ../../../../soc/rtl/sim
make run PROGRAM=../../src/examples/test_video/program.hex

Graphics Accelerator Simulation

cd rtl/sim
make run

• Press 1 to select the cube model;
• Press 2 to select the teapot model;
• Press W/A/S/D and arrows to move the camera;
• Press SPACE to start/stop the rotation of the model;
• Press TAB to enable/disable the wireframe mode;
• Press T to enable/disable texture mapping;
• Press L to increase the number of directional lights;
• Press G to enable/disable Gouraud shading.

Acknowledgements

• The SoC is based on the Oberon project for the ULX3S available here: https://github.com/emard/oberon
• The CPU is based on icicle v1 available here: https://github.com/grahamedgecombe/icicle/tree/v1

graphite's Issues

Frame buffer and textures at any SDRAM address

We want to give the full addressing range for the frame buffer and textures and no longer need to use OP_WRITE_TEX.

Texture 256x2048 not properly mapped

Screen not fully cleared in grey after a reset

For some reason, the cache flush is not performed after clearing the screen in BIOS.

Optimize calculations using Goldschmidt Algorithm

Compute fixed-point square roots and their reciprocals using Goldschmidt algorithm.
Ref.: https://www.fpgarelated.com/showarticle/1347.php

Small horizontal screen offset to the right

The screen has a small horizontal offset to the right. Same for all modes.

Optimize variable texture dimensions

Since commit 0b88df6, we are no longer able to reach the CPU speed of 80MHz with the fast CPU option. Check if there is a way to optimize this.

Rasterization fill convention with top-left rule

Ref.: https://github.com/gustavopezzi/triangle-rasterizer-fix16

Integrate Graphite core in the SoC

Compute edge functions only once and use delta values

https://github.com/gustavopezzi/triangle-rasterizer-fix16

Textured surfaces are not properly rendered

Some texels are missing. The reference implementation is fine.

Frame buffer format RGB565

This is the native format for LVGL in 16-bit.

Need to dequeue twice the serial FIFO

We need to dequeue twice instead of once the serial FIFO.