⇡ Untethered lowRISC tutorial

A guide to the development environment

System requirement

We recommend you work with a 64-bit Ubuntu (14.04 LTS) system with GNU GCC >= 4.8 installed. If necessary, create such a setup using VMware Workstation Player or VirtualBox.

The default simulator for RTL/Behavioural SystemVerilog simulation is Verilator. Please download and install a latest version for the best SystemVerilog support.

An FPGA demonstration is provided using either a Xilinx Kintex-7 FPGA KC705 evaluation kit or a low-end Nexys™4 DDR Artix-7 FPGA Board. The KC705 kit comes with a device and node locked license for Xilinx Vivado Design Suite. The default version for FPGA demonstration project is Vivado 2015.4(64-bit). As for the users of the Nexys4-DDR boards, please acquire a free license and install the WebPACK edition of Vivado.

By default, all simulations produce waveforms in the VCD format.
GTKWave can be used to view VCD files.

Here shows software versions and environment variables on my machine:

 # it is better to use bash
 $ echo $0

 $ uname -s -v -r -i -o
 Linux 3.13.0-66-generic #108-Ubuntu SMP Wed Oct 7 15:20:27 UTC 2015 x86_64 GNU/Linux

 # make sure the RISCV variable is exposed
 $ echo $RISCV

 $ gcc --version
 gcc (Ubuntu 4.8.4-2ubuntu1~14.04) 4.8.4
 Copyright (C) 2013 Free Software Foundation, Inc.
 This is free software; see the source for copying conditions.  There is NO

 $ which verilator

 $ gtkwave --version
 GTKWave Analyzer v3.3.58 (w)1999-2014 BSI

 This is free software; see the source for copying conditions.  There is NO

 $ which vivado

 # make sure the XILINX_VIVADO variable is exposed

Ensure you have all the necessary packages installed before attempting to build the RISC-V tools:

sudo apt-get install autoconf automake autotools-dev curl \
  libmpc-dev libmpfr-dev libgmp-dev gawk build-essential bison \
  flex texinfo gperf libncurses5-dev libusb-1.0-0 libboost-dev \

Download the code release

The lowRISC chip git repository is hosted on GitHub . Instead of cloning individual sub-modules, we recommend cloning the entire repository to ensure all the sub-modules you acquire are compatible. Different versions of the sub-modules are not guaranteed to work.

To clone the whole lowRISC chip git repository:

# clone the repository to your home directory:
cd ~/lowRISC/DIR
# get the branch untether-v0.2
git clone -b untether-v0.2 --recursive https://github.com/lowrisc/lowrisc-chip.git
cd lowrisc-chip

There are 3 main branches:

  • master : The major release branch, default, most stable. After major releases, only bugfixes related to the latest release are merged.
  • dev : The minor release branch, less stable. After major releases, new features are added to this branch waiting for the next major release.
  • update : The active development branch, non-stable. The branch for developing new features, testing bugfixes, and experimenting with new ideas.

To setup the necessary RISC-V variables use the setup script found at lowrisc-chip/set_riscv_env.sh:

# source this file
echo "Setting up lowRISC/RISC-V environment..."
echo "Make sure you source this script at the top of lowrisc-chip."
# Variables for lowRISC/RISC-V
if [ "$TOP" == "" ]; then
    echo "\$TOP is not available."
    echo "Set \$TOP to the top of lowrisc-chip which is the current directory."
    export TOP=$PWD
export RISCV=$TOP/riscv
export PATH=$PATH:$RISCV/bin
# choose the FPGA board (KC705 in default)
export FPGA_BOARD=kc705

Structure of the git repository

  • chisel: The Chisel compiler used for compiling the rocket system.
  • fpga: FPGA demo implementations
    • board: Demo projects for individual development boards. [FPGA Demo]
      • kc705: Files for the Xilinx KC705 development board.
      • nexys4: Files for the Nexys™4 DDR Artix-7 FPGA Board.
  • hardfloat: The IEEE 754-2008 compliant floating-point unit.
  • junctions: Peripheral components and I/O devices associated with the RocketChip.
  • project: Global configuration for Chisel compilation.
  • riscv-tools: The cross-compilation and simulation tool chain. [Compile and install RISC-V cross-compiler]
    • riscv-fesvr: The front-end server that serves system calls on the host machine.
    • riscv-gnu-toolchain: The GNU GCC cross-compiler for RISC-V ISA.
    • riscv-isa-sim: The RISC-V ISA simulator Spike [Behavioural Simulation (Spike)]
    • riscv-opcodes: The enumeration of all RISC-V opcodes executable by the Spike simulator.
    • riscv-pk: The proxy kernel need for running legacy programs in the Spike simulator.
    • riscv-tests: Tests for the Rocket core.
  • rocket: The Chisel code for the Rocket core.
  • socip: The SystemVerilog/Verilog building blocks used in lowRISC chip.
    • nasti: A SystemVerilog implementaion of NASTI/NASTI-Lite on-chip interconnection.
  • src: The top level code of lowRISC chip.
    • main: The Chisel/Verilog code for hardware implementation.
    • test: The Verilog/C++(DPI) test bench files
  • uncore: The Chisel code of the memory subsystem.
  • vsim: RTL/Behavioural SystemVerilog simulation environment. [RTL simulation]

Compiling and installation of individual tools/packages