Learning FPGA, yosys, nextpnr, and RISC-V
Mission statement: create teaching material for FPGAs, processor design and RISC-V, using around $40 per students.
FemtoRV is a minimalistic RISC-V design, with easy-to-read Verilog sources directly written from the RISC-V specification. The most elementary version (quark), an RV32I core, weights 400 lines of VERILOG (documented version), and 100 lines if you remove the comments. There are also more elaborate versions, the biggest one (petitbateau) is an RV32IMFC core. The repository also includes a companion SoC, with drivers for an UART, a led matrix, a small OLED display, SPI RAM and SDCard. Its most basic configuration fits on the Lattice IceStick (< 1280 LUTs). It can be used for teaching processor design and RISC-V programming.
The repository includes LiteX examples. The LiteX framework is a well designed and an easy-to-use framework to create SoCs. It lets you create a SoC by assembling components (processor, SDRAM controller, SDCard controller, USB, ...) in Python. FemtoRV is directly supported by LiteX (that directly downloads it from this repository when selected as the SoC's processor).
In this tutorial, you will learn to build your own RISC-V processor, step by step, starting from the simplest design (that blinks a LED), to a fully functional RISC-V core that can compute and display graphics.
Files are here. This includes:
- Blinker: the "hello world" program
- LedMatrix: play with a 8x8 let matrix, driven by a MAX7219 IC.
- OLed: play with a SSD1351 OLed display, driven by a 4-wire SPI protocol.
- Serial: access the included USB-virtual UART pins
- LedTerminal: display scrolling messages on the LED matrix, obtained from the USB virtual UART
- FOMU: simple examples for the "FPGA in a USB dongle", including the FrankenVGA experiment !
- ULX3S HDMI: simple self-contained heavily commented HDMI example.