Ibex Demo System

This an example RISC-V SoC targeting the Arty-A7 FPGA board. It comprises the lowRISC Ibex core along with the following features:

• RISC-V debug support (using the PULP RISC-V Debug Module)
• UART
• GPIO
• PWM
• Timer
• SPI
• A basic peripheral to write ASCII output to a file and halt simulation from software

Debug can be used via a USB connection to the Arty-A7 board. No external JTAG probe is required.

Software Requirements

• Xilinx Vivado - https://www.xilinx.com/support/download.html
• rv32imc GCC toolchain - lowRISC provides one: https://github.com/lowRISC/lowrisc-toolchains/releases (For example: lowrisc-toolchain-rv32imcb-20220524-1.tar.xz)
• cmake
• python3 - Additional python dependencies in python-requirements.txt installed with pip
• openocd (version 0.11.0 or above)
• screen
• srecord

Container Guide

There is a prebuilt container of tools available you may want to use to get started quickly. There are instructions for building the container for either Docker/Podman located in ./container/README.md.

Linux/MacOS

A container image may be provided to you in the form of a tarball. You can load the containerfile by running:

sudo docker load < ibex_demo_image.tar
# OR
podman load < ibex_demo_image.tar

If you already have a container file, you can start the container by running:

sudo docker run -it --rm \
  -p 6080:6080 \
  -p 3333:3333 \
  -v $(pwd):/home/dev/demo:Z \
  ibex

OR

podman unshare chown 1000:1000 -R .
podman run -it --rm \
  -p 6080:6080 \
  -p 3333:3333 \
  -v $(pwd):/home/dev/demo:Z \
  ibex
podman unshare chown 0:0 -R .

To access the container once running, go to http://localhost:6080/vnc.html.

If you want to program the FPGA from the container, let's find out which bus and device the Arty is on:

$ lsusb
...
Bus 00X Device 00Y: ID 0403:6010 Future Technology Devices International, Ltd FT2232C/D/H Dual UART/FIFO IC
...

Where X and Y are numbers. Please note down what X and Y is for you (this will change if you unplug and replug your FPGA).

Then run Docker with the following parameters:

sudo docker run -it --rm \
  -p 6080:6080 \
  -p 3333:3333 \
  -v $(pwd):/home/dev/demo:Z \
  --privileged \
  --device=/dev/bus/usb/00X/00Y \
  --device=/dev/ttyUSB1 \
  ibex

Windows

Run a command prompt in administrator mode and type:

cd "C:\Program Files\Docker\Docker"
.\DockerCli.exe -SwitchLinuxEngine

In case you have a tarball of the docker image, run:

docker load -i ibex_demo_image.tar

Go to the folder where you have decompressed the demo system repository:

docker run -it --rm -p 6080:6080 -p 3333:3333 -v %cd%:/home/dev/demo:Z ibex

Add udev rules for our device

For both the container and the native setups you will need to add user device permissions for our FPGA board. The following instructions are for Linux-based systems and are needed for the programmer to access the development board.

Arty-A7

sudo su
cat <<EOF > /etc/udev/rules.d/90-arty-a7.rules
# Future Technology Devices International, Ltd FT2232C/D/H Dual UART/FIFO IC
# used on Digilent boards
ACTION=="add|change", SUBSYSTEM=="usb|tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6010", ATTRS{manufacturer}=="Digilent", MODE="0666"

# Future Technology Devices International, Ltd FT232 Serial (UART) IC
ACTION=="add|change", SUBSYSTEM=="usb|tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", MODE="0666"
EOF

exit

openFPGAloader

sudo su
cat <<EOF > /etc/udev/rules.d/99-openfpgaloader.rules
# Copy this file to /etc/udev/rules.d/

ACTION!="add|change", GOTO="openfpgaloader_rules_end"

# gpiochip subsystem
SUBSYSTEM=="gpio", MODE="0664", GROUP="plugdev", TAG+="uaccess"

SUBSYSTEM!="usb|tty|hidraw", GOTO="openfpgaloader_rules_end"

# Original FT232/FT245 VID:PID
ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", MODE="664", GROUP="plugdev", TAG+="uaccess"

# Original FT2232 VID:PID
ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6010", MODE="664", GROUP="plugdev", TAG+="uaccess"

# Original FT4232 VID:PID
ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6011", MODE="664", GROUP="plugdev", TAG+="uaccess"

# Original FT232H VID:PID
ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6014", MODE="664", GROUP="plugdev", TAG+="uaccess"

# Original FT231X VID:PID
ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6015", MODE="664", GROUP="plugdev", TAG+="uaccess"

# anlogic cable
ATTRS{idVendor}=="0547", ATTRS{idProduct}=="1002", MODE="664", GROUP="plugdev", TAG+="uaccess"

# altera usb-blaster
ATTRS{idVendor}=="09fb", ATTRS{idProduct}=="6001", MODE="664", GROUP="plugdev", TAG+="uaccess"
ATTRS{idVendor}=="09fb", ATTRS{idProduct}=="6002", MODE="664", GROUP="plugdev", TAG+="uaccess"
ATTRS{idVendor}=="09fb", ATTRS{idProduct}=="6003", MODE="664", GROUP="plugdev", TAG+="uaccess"

# altera usb-blasterII - uninitialized
ATTRS{idVendor}=="09fb", ATTRS{idProduct}=="6810", MODE="664", GROUP="plugdev", TAG+="uaccess"
# altera usb-blasterII - initialized
ATTRS{idVendor}=="09fb", ATTRS{idProduct}=="6010", MODE="664", GROUP="plugdev", TAG+="uaccess"

# dirtyJTAG
ATTRS{idVendor}=="1209", ATTRS{idProduct}=="c0ca", MODE="664", GROUP="plugdev", TAG+="uaccess"

# Jlink
ATTRS{idVendor}=="1366", ATTRS{idProduct}=="0105", MODE="664", GROUP="plugdev", TAG+="uaccess"

# NXP LPC-Link2
ATTRS{idVendor}=="1fc9", ATTRS{idProduct}=="0090", MODE="664", GROUP="plugdev", TAG+="uaccess"

# NXP ARM mbed
ATTRS{idVendor}=="0d28", ATTRS{idProduct}=="0204", MODE="664", GROUP="plugdev", TAG+="uaccess"

# icebreaker bitsy
ATTRS{idVendor}=="1d50", ATTRS{idProduct}=="6146", MODE="664", GROUP="plugdev", TAG+="uaccess"

# orbtrace-mini dfu
ATTRS{idVendor}=="1209", ATTRS{idProduct}=="3442", MODE="664", GROUP="plugdev", TAG+="uaccess"

LABEL="openfpgaloader_rules_end"

EOF

exit

Run the following to reload the rules:

sudo udevadm control --reload-rules
sudo udevadm trigger

Add user to plugdev group:

sudo usermod -a $USER -G plugdev

Installing environment using Nix (*alternative*)

Nix Environment Setup

An alternative system for installing all of the project dependencies is provided using the Nix package manager. Once installed and the dependencies are fetched from the internet, you can enter a shell with all of the software required for building by running the command nix develop in the root directory of the project. To leave this environment, simply run exit.

Installing

Installing Nix

# Run the recommended nix multi-user installation
# https://nixos.org/download.html
# This is an interactive installer, just follow the prompts...
sh <(curl -L https://nixos.org/nix/install) --daemon

# Add some global configuration to nix to make use of the flakes and CLI experimental features.
mkdir -p $HOME/.config/nix
cat <<EOF > $HOME/.config/nix/nix.conf
experimental-features = nix-command flakes
warn-dirty = false
EOF

# Disable signatures when using nix copy to import from a store
# This allows us to easily import from a cache on a local USB
sudo su
mkdir -p /etc/nix
cat <<EOF >> /etc/nix/nix.conf
require-sigs = false
EOF
exit

# Reload the nix daemon to commit the config above
sudo systemctl restart nix-daemon.service

# You may now need to reload your shell, but check that nix is working by running this:
nix --version
> nix (Nix) 2.12.0

Installing Vivado using Nix

# Go to the Xilinx.com website
# https://www.xilinx.com/support/download.html
# Download the 2022.2 Unified Installer for Linux
# The link looks like:
# <Xilinx Unified Installer 2022.2: Linux Self Extracting Web Installer (BIN - 271.02 MB)>
# The download link will be similar to:
# https://www.xilinx.com/member/forms/download/xef.html?filename=Xilinx_Unified_2022.2_1014_8888_Lin64.bin
# - You will need to register on the website to download this file.

# Once the download is complete...
cd <location/of/downloaded/file>

# Extract the installer to a local temporary directory
PREFIX=/tmp/xilinx
VERSION=2022.2
INSTALLER="<downloaded/file>"  # This should match the download
INSTALLER_EXTRACTED="${PREFIX}/extracted"
mkdir $PREFIX
chown -R $USER:$USER $PREFIX $INSTALLER
chmod +x $INSTALLER
./$INSTALLER --keep --noexec --target $INSTALLER_EXTRACTED

# Now run this installer graphically, to create a new bundled-installer with the device support we need for the Arty-A7.
INSTALLER_BUNDLED="$PREFIX/bundled"
pushd $INSTALLER_EXTRACTED
./xsetup
popd

• Running './xsetup' above should have popped up the graphical installation wizard.
  1. Page '<LANDING_PAGE>'
     1. Select 'Next >'
  2. Page 'Select Install Type'
     1. Enter email/password for 'User Authentication' (register on Xilinx.com)
     2. Select the radio-box 'Download Image (Install Seperately)'
     3. Select the download directory as '/tmp/xilinx/bundled' (the value from $INSTALLER_BUNDLED, See above)
     4. Under 'Download fields to create full image for selected platform(s)', select 'Linux' only.
     5. Under 'Image Contents', select 'Selected Product Only'
     6. Select 'Next >'
  3. Page 'Select Product to Install'
     1. Select the radio-box 'Vivado' only
     2. Select 'Next >'
  4. Page 'Select Edition to Install'
     1. Select the radio-box 'Vivado ML Standard'
     2. Select 'Next >'
  5. Page 'Vivado ML Standard'
     1. Ensure only the following boxes are selected....
        1. Design Tools - Vivado Design Suite - {Vivado, Vitis HLS}
        2. Devices - Production Devices - 7 Series - {Artix7, Kintex7, Spartan7}
        3. Installation Options
     2. Select 'Next >'
  6. Page 'Download Summary'
     1. Check the download is approx 13GB.
     2. Select 'Download'

# Now we have created a bundled installer for Vivado, we need to add this to the nix store

# The easiest way to get the data into the nix store is by creating an archive...
pushd $PREFIX
BUNDLED_ARCHIVE="$PREFIX/vivado_bundled.tar.gz"
# (You may need to install 'pigz' for this step, e.g. 'sudo apt install pigz')
tar cf $BUNDLED_ARCHIVE -I pigz --directory=$(dirname $INSTALLER_BUNDLED) ./$(basename $INSTALLER_BUNDLED)

# Now add using 'nix-prefetch-url'
VIVADO_BUNDLED_HASH=$(nix-prefetch-url --type sha256 file:$BUNDLED_ARCHIVE)

# The value of this hash will be needed for the next step.
echo $VIVADO_BUNDLED_HASH
popd

Install dependencies and activate our environment

We can use the nix flake.nix recipe to build our environment.

git clone git@github.com:lowRISC/ibex-demo-system.git
cd ibex-demo-system

# [OPTIONAL]
# Copy dependencies from a pre-prepared USB stick to compensate for bad internet
# The hash below is the expected hash of the lab dependencies
usb_path="<path/to/usb>" # e.g. "/media/harry/KINGSTON"
nix copy \
  --no-require-sigs \
  --from file://${usb_path}/nix/store/ \
  /nix/store/kx1qnhs2b6ikn5s4mj7jpj84rasqwc2h-labenv

pushd dependencies && nix flake update && popd && nix flake update
nix develop

# Once it completes,you should see the lowRISC logo, followed by...
# >> ------------------------------------------------- <<
# >> Welcome the the ibex-demo-system nix environment! <<
# >> ------------------------------------------------- <<

# You are now in a shell with all the tools required to do the lab.

# To exit this shell environment when you are done, simply run
exit

# Bonus Nix
# Use nix-tree to interactively examine all dependencies of the demo.
nix run nixpkgs#nix-tree -- .#devShells.x86_64-linux.default --derivation

Vivado-specific change (only needed if enabled in flake.nix):

# Run this before the `nix flake update` above.

# Update the flake.nix with the hash ($VIVADO_BUNDLED_HASH) of the vivado installer
# (We need to update just the sha256 hash input of requireFile function.)
sed -i -- "s|sha256\s=\s\".*\";|sha256 = \"$VIVADO_BUNDLED_HASH\";|g" dependencies/flake.nix

Native Python Environment

(NOT NEEDED IN THE CONTAINER ENVIRONMENT)

To install python dependencies use pip, you may wish to do this inside a virtual environment to avoid disturbing you current python setup (note it uses a lowRISC fork of edalize and FuseSoC so if you already use these a virtual environment is recommended):

# Setup python venv
python3 -m venv .venv
source .venv/bin/activate

# Install python requirements
pip3 install -r python-requirements.txt

You may need to run the last command twice if you get the following error: ERROR: Failed building wheel for fusesoc

Building Software

C stack

First the software must be built. This can be loaded into an FPGA to run on a synthesized Ibex processor, or passed to a verilator simulation model to be simulated on a PC.

mkdir sw/c/build
pushd sw/c/build
cmake ..
make
popd

Rust stack

pushd sw/rust
cargo build --bin led
popd

For more details, please refer to Ibex Rust stack.

Note the FPGA build relies on a fixed path to the initial binary (blank.vmem) so if you want to create your build directory elsewhere you need to adjust the path in ibex_demo_system.core

Building Simulation

The Demo System simulator binary can be built via FuseSoC. From the Ibex repository root run:

fusesoc --cores-root=. run --target=sim --tool=verilator --setup --build lowrisc:ibex:demo_system

Running the Simulator

Having built the simulator and software, to simulate using Verilator we can use the following commands. <sw_elf_file> should be a path to an ELF file (or alternatively a vmem file) built as described above. Use ./sw/c/build/demo/hello_world/demo to run the demo binary.

Run from the repository root run:

# For example :
./build/lowrisc_ibex_demo_system_0/sim-verilator/Vtop_verilator \
  --meminit=ram,./sw/c/build/demo/hello_world/demo

# You need to substitute the <sw_elf_file> for a binary we have build above.
./build/lowrisc_ibex_demo_system_0/sim-verilator/Vtop_verilator [-t] --meminit=ram,<sw_elf_file>

Pass -t to get an FST trace of execution that can be viewed with GTKWave.

Simulation statistics
=====================
Executed cycles:  5899491
Wallclock time:   1.934 s
Simulation speed: 3.05041e+06 cycles/s (3050.41 kHz)

Performance Counters
====================
Cycles:                     457
NONE:                       0
Instructions Retired:       296
LSU Busy:                   108
Fetch Wait:                 20
Loads:                      53
Stores:                     55
Jumps:                      21
Conditional Branches:       12
Taken Conditional Branches: 7
Compressed Instructions:    164
Multiply Wait:              0
Divide Wait:                0

Building FPGA bitstream

FuseSoC handles the FPGA build. Vivado tools must be setup beforehand. From the repository root:

fusesoc --cores-root=. run --target=synth --setup --build lowrisc:ibex:demo_system

The default board is the Arty A7, but you can also use different synthesis targets. For example, to use the Sonata board change the target to synth_sonata.

Programming FPGA

To program the FPGA, either use FuseSoC again

fusesoc --cores-root=. run --target=synth --run lowrisc:ibex:demo_system

# If the above does not work, try executing the programming operation manually with..
make -C ./build/lowrisc_ibex_demo_system_0/synth-vivado/ pgm

You can also use OpenFPGALoader, here are some example commands:

# Programming the Arty A7
./openFPGALoader -b arty_a7_35t build/lowrisc_ibex_demo_system_0/synth-vivado/lowrisc_ibex_demo_system_0.bit

# Programming the Sonata board
./openFPGALoader -c ft4232 build/lowrisc_ibex_demo_system_0/synth_sonata-vivado/lowrisc_ibex_demo_system_0.bit

Loading an application to the programmed FPGA

The util/load_demo_system.sh script can be used to load and run an application. You can choose to immediately run it or begin halted, allowing you to attach a debugger.

# Run demo
./util/load_demo_system.sh run ./sw/c/build/demo/hello_world/demo
./util/load_demo_system.sh run ./sw/c/build/demo/lcd_st7735/lcd_st7735

# Load demo and start halted awaiting a debugger
./util/load_demo_system.sh halt ./sw/c/build/demo/hello_world/demo

# Run demo on the Sonata board
./util/load_demo_system.sh run ./sw/c/build/demo/hello_world/demo ./util/sonata-openocd-cfg.tcl

To view terminal output use screen:

# Look in /dev to see available ttyUSB devices
screen /dev/ttyUSB1 115200

If you see an immediate [screen is terminating], it may mean that you need super user rights. In this case, you may try using sudo.

To exit from the screen command, you should press ctrl-a followed by k. You will need to confirm the exit by pressing y.

Debugging an application

Either load an application and halt (see above) or start a new OpenOCD instance:

openocd -f util/arty-a7-openocd-cfg.tcl

Then run GDB against the running binary and connect to localhost:3333 as a remote target:

riscv32-unknown-elf-gdb ./sw/c/build/demo/hello_world/demo

(gdb) target extended-remote localhost:3333