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RISC-V Playground

    If you want to dive into the RISC-V architecture, have a look at the RISC-V Playground.

    This projects contains a beginner friendly RISC-V ‘fantasy microcontroller’ for the FPGA featuring a RV32IMC processor and a selection of peripherals:

    • Textmode LCD driver with 7-Bit ASCII font
    • Random number generator
    • GPIO registers for PMOD pin access
    • Timer tick interrupt
    • LEDs
    • UART terminal, 115200 Baud 8N1
    • 1 kb initialised RAM for bootloader
    • 128 kb RAM initialised using file read interface over SPI

    Detailed descriptions, memory map and register set are described in the README file.

    Docs on RISC-V itself

    Quickstart

    Clone both the bitstream tools repo

    git clone https://github.com/badgeteam/mch2022-tools/

    and the FPGA repo

    git clone --recursive https://github.com/badgeteam/mch2022-firmware-ice40/

    go to the

    mch2022-firmware-ice40/projects/RISCV-Playground/

    folder and load both the bitstream for the FPGA and a RISC-V binary:

    webusb_fpga.py riscv-playground.bin 0xdabbad00:fw/tinyblinky/tinyblinky.bin

    Connect to the serial terminal using your favourite terminal emulator with 115200 baud 8N1 LF on ttyACM1.

    Get RISC-V assembler

    The GNU binutils for RISC-V include the assembler.

    Unlike as for the FPGA tools that change rapidly, you can just have a look for binary packages in your distribution.

    For Debian 11 Stable “Bullseye”, one gets using

    apt-cache search binutils | grep riscv

    binutils-riscv64-linux-gnu - GNU binary utilities, for riscv64-linux-gnu target
binutils-riscv64-linux-gnu-dbg - GNU binary utilities, for riscv64-linux-gnu target (debug symbols)
binutils-riscv64-unknown-elf - GNU assembler, linker and binary utilities for RISC-V processors

    Both binutils-riscv64-linux-gnu and binutils-riscv64-unknown-elf are fine, but you might have to adjust the actual invocations to the tools depending on which package(s) you actually installed.

    Despite the names, these also support 32 bit RISC-V targets.

    Example firmware

    Bootloader

    This one is included into the bitstream for default. It initialises the LCD display and initialises the 128 kb RAM from file “0xdabbad00” using the file read interface over SPI provided by the ESP32 firmware.

    Tinyblinky

    A little blinky in RISC-V assembler. A nice “hello world” project.

    Interrupt

    An example on how to use interrupts on RISC-V, including notes on compressed opcodes and and small tools for printing hex numbers.

    Mandelbrot

    Explore the Mandelbrot and Tricorn fractals in ASCII art. This example shows how to use the LCD and buttons in assembler.

    Hello GCC

    A small project in C featuring serial terminal, buttons, LED and LCD.

    Forth

    This is a port of Mecrisp-Quintus, a 32 Bit Forth implementation, available under GPL3.

    For more info, get the full release of Mecrisp-Quintus here:

    http://mecrisp.sourceforge.net/

    Useful for debugging, and maybe for you, too.

    If you have not used Forth before, better start with this implementation of Forth that comes with much more badge support code.