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Freedom Unleashed Software Development Kit

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SiFive Freedom Unleashed SDK

The new experimental Freedom Unleashed (FU) SDK is based on OpenEmbedded (OE). Using OE you will be able to:

  • build predefined disk images for QEMU, SiFive HiFive Unleashed development board and SiFive HiFive Unmatched;
    • Note: The support for HiFive Unleashed Expansion board from Microsemi is now removed from SiFive OpenEmbedded layer (i.e. meta-sifive). If you have the expansion board we advice you to switch to Microchip PolarFire SoC Yocto BSP which includes support for MPFS-DEV-KIT (HiFive Unleashed Expansion Board) directly from the manufacturer. You are also welcome to use older releases (2021.02.00 or older) from SiFive OpenEmbedded layer.
    • Note: 2021.02.00 release introduces the support for the SiFive HiFive Unmatched board (pre-production 8GB variant). Contact your SiFive representative before using disk images built for
      machine on your particular board. If you received the final board (16GB) variant via Mouser or CrowdSupply you should skip 2021.02.00 release and use 2021.03.00 (or newer).
  • build custom disk images with additional software packages from various third-party OE layers;
  • quickly launch QEMU VM instance with your built disk image;
  • build bootloader binaries (OpenSBI, U-Boot, U-Boot SPL);
  • build Device Tree Binary (DTB);
  • build Linux kernel images;
  • easily modify disk partition layout.

For more information on particular release see

directory in freedom-u-sdk repository on GitHub.

For advanced OE usage we advice to look into Yocto Project Documentation and A practical guide to BitBake.

Quick Start


command from Google if not available on your host system. Please follow the official instructions by Google.

Then install a number of packages for BitBake (OE build tool) to work properly on your host system. BitBake itself depends on Python 3. Once you have Python 3 installed BitBake should be able to tell you most of the missing packages.

For Ubuntu 18.04 (or newer) install python3-distutils package.

Detailed instructions for various distributions can be found in "Required Packages for the Build Host" section in Yocto Project Reference Manual.

Creating Workspace

This needs to be done every time you want a clean setup based on the latest layers.

mkdir riscv-sifive && cd riscv-sifive
repo init -u git:// -b 2021.10 -m tools/manifests/sifive.xml
repo sync

Creating a Working Branch

If you want to make modifications to existing layers then creating working branches in all repositories is advisable.

repo start work --all

Getting Build Tools (optional)

OpenEmbedded-Core requires GCC 6 or newer to be available on the host system. Your host system might have an older version of GCC if you use LTS (Long Term Support) Linux distribution (e.g. Ubuntu 16.04.6 has GCC 5.4.0). You could solve this issue by installing build tools. This requires less than 400MB of disk space. You can download pre-built one or build your own build tools.

Option 1: Installing OpenEmbedded-Core Build Tools (Pre-Built)

./openembedded-core/scripts/install-buildtools -r yocto-3.2_M2 -t 20200729

The native SDK will be installed under


Finally you should be able to use build tools:

. ./openembedded-core/buildtools/environment-setup-x86_64-pokysdk-linux

Option 2: Building Your Own Build Tools

Your host needs to have GCC 6 (or newer) or build tools installed from Option 1.

You can find pre-built tools from the same release source in GitHub release assets.

To build your own build tools execute the command below:

bitbake buildtools-extended-tarball

You can find the native SDK under


Now you can install build tools:

$BUILDDIR/tmp-glibc/deploy/sdk/ -d $BUILDDIR/../openembedded-core/buildtools -y

Finally you should be able to use your build tools:

. $BUILDDIR/../openembedded-core/buildtools/environment-setup-x86_64-oesdk-linux

Setting up Build Environment

This step has to be done after you modify your environment with toolchain you want to use otherwise wrong host tools might be available in the package build environment. For example,

from host system will be used for building
. ./freedom-u-sdk/

You can verify and fix your host tools by checking symlinks in


Configuring BitBake Parallel Number of Tasks/Jobs

There are 3 variables that control the number of parallel tasks/jobs BitBake will use:

. The last two are the most important, and both are set to number of cores available on the system. You can set them in your
or in your shell environment similar to how
is used (see next section). Example:
PARALLEL_MAKE="-j 4" BB_NUMBER_THREADS=4 MACHINE=freedom-u540 bitbake demo-coreip-cli

Leaving defaults could cause high load averages, high memory usage, high IO wait and could make your system unresponsive due to resources overuse. The defaults should be changed based on your system configuration.

Building Disk Images

There are two disk image targets added by FUSDK:

  • demo-coreip-cli
    - basic command line image (recommended);
  • demo-coreip-xfce4
    - basic graphical disk image with Xfce 4 desktop environment.

There are several machine targets defined:

  • qemuriscv64
    - RISC-V 64-bit (RV64GC) for QEMU virt machine (recommended for QEMU target).
  • freedom-u540
    - SiFive HiFive Unleashed development board.
  • unmatched
    - SiFive HiFive Unmatched development board.

The QEMU machines with the additional extensions (i.e. beyond RV64GC) do not affect how packages or/and disk images are built. This means the toolchain might not provide support for the new extensions. By default packages are not built with the new instructions enabled.

Building disk images is CPU intensive, could require <10GB of sources downloaded over the Internet and <200GB of local storage.

Building disk image takes a single command which may take anything from 30 minutes to several hours depending on your hardware. Examples:

MACHINE=qemuriscv64 bitbake demo-coreip-cli
MACHINE=freedom-u540 bitbake demo-coreip-cli
MACHINE=unmatched bitbake demo-coreip-xfce4

Running in QEMU

OE provides easy to use wrapper for QEMU:

MACHINE=qemuriscv64 runqemu nographic slirp

Running on Hardware

You will find all available build fragments (incl. disk images) in


Disk images files use

format, for example,

. We are interested in
disk images for writing to uSD card.

Be very careful while picking /dev/sdX device! Look at dmesg, lsblk, blkid, GNOME Disks, etc. before and after plugging in your uSD card to find a proper device. Double check it to avoid overwriting any of system disks/partitions!

Unmount any mounted partitions from uSD card before writing!

We advice to use 32GB uSD cards. 8GB cards (shipped with HiFive Unleashed) can still be used with

CLI images.

Finally write uSD card:

xzcat demo-coreip-cli-freedom-u540.wic.xz | sudo dd of=/dev/sdX bs=512K iflag=fullblock oflag=direct conv=fsync status=progress

MSEL for Unleashed

You will need to modify MSEL to allow using U-Boot SPL, OpenSBI, U-Boot proper bootloaders from uSD card instead of SPI-NOR Flash chip:

      USB   LED    Mode Select                  Ethernet
 |                | | | | |X| |                 |      |   |
 |                | | | | | | |                 |      |   |
 |        HFXSEL->|X|X|X|X| |X|                 |______|   |
 |                +-+-+-+-+-+-+                            |
 |        RTCSEL-----/ 0 1 2 3 

MSEL for Unmatched

By default MSEL on Unmatched is set to use uSD instead of SPI-NOR Flash chip to load U-Boot SPL, OpenSBI and U-Boot proper. Below is the default configuration for DIP switches (located next to Assembly Number and RTC battery):

  +----------> CHIPIDSEL
  | +--------> MSEL3
  | | +------> MSEL2
  | | | +----> MSEL1
  | | | | +--> MSEL0
  | | | | |
 | |X| |X|X| ON(1)
 | | | | | |
 |X| |X| | | OFF(0)

Connecting Using Serial Console

Connect your HiFive Unleashed or HiFive Unmatched to your PC using microUSB-USB cable to access serial console.

For macOS, run:

screen -L /dev/tty.usbserial-*01 115200

For Linux, run:

screen -L /dev/serial/by-id/usb-FTDI_Dual_RS232-HS-if01-port0 115200

The above commands might vary depending on your exact setup.

command will log all output to
in your current working directory.

To quit screen, hit

Ctrl - A
followed by
symbol. Finally agree to terminate all windows by typing

You can login with

account. The password is
. We strongly recommend to change the default password for the root account on the first boot before you connect it to the Internet.

Connecting Using SSH

Before you connect your board to the Internet we strongly recommend to change the default password for the root account and configure your network equipment (for example, routers and firewalls) appropriately.

SSH daemon is not enabled by default. To enable SSH daemon connect to the board using serial console method described above. Once connected execute the following commands:

systemctl enable sshd.socket
systemctl start sshd.socket

The HiFive Unleashed and Unmatched behave like any other network capable device (such as PC, laptop, and Single Board Computers like Raspberry Pi). Connect the board to your network (for example, a router), and it will acquire IPv4 + DNS configuration using DHCP protocol. You can use your router management panel to get assigned IPv4 address or use the serial console to acquire it directly from the board (use

ip addr
command to print active network information). Finally you can SSH to the board:
ssh -o PreferredAuthentications=password -o PubkeyAuthentication=no -o StrictHostKeyChecking=no -o "UserKnownHostsFile /dev/null" [email protected]

Supported GPUs

Various GPUs from AMD were successfully tested with the boards. In particular Radeon HD 6450 is the most widely used. Other GPUs from the same family might also work, for instance, THD64xxM, HD7450, HD8450, R5 230, R5 235, R5 235X. The newest tested GPUs from AMD are RX 550, RX 570, RX 580 with no issues.

Online Resizing of rootfs (Root File Partition)

It is highly advised to resize partitions offline (i.e. before booting the system). If you already booted the system and cannot do offline resizing then the following instructions should resize rootfs (root file partition) to full uSD capacity:

sgdisk -v /dev/mmcblk0
sgdisk -e /dev/mmcblk0
parted /dev/mmcblk0 resizepart 4 100%
resize2fs /dev/mmcblk0p4

Support TensorFlow Lite tflite_runtime Python library

You can deploy your TensorFlow lite model by importing the Tensorflow Lite interpreter. There is a sample code
avaliable to demostrate how to deploy model and test MNIST hadwritten digits.
cd /usr/share/doc/python3-tensorflow-lite-demo/example

Contributions & Feedback

If you want to file issues, send patches and make feature/enhancement requests use meta-sifive or freedom-u-sdk repositories on GitHub.

You are also welcome to join SiFive Forums where we have HiFive Unleashed and HiFive Unmatched categories for discussions.

Known Issues

  1. There is no CPUFreq support enabled on HiFive Unmatched.

  2. OpenEmbedded Core (and thus FUSDK) does not support eCryptFS or any other file system without long file names support. File systems must support filenames up to 200 characters in length.

  3. BitBake requires UTF-8 based locale (e.g.

    ). You can choose any locale as long as it is UTF-8. This usually happens in containers (e.g. ubuntu:18.04). You can verify your locale by running
    command. On Ubuntu 18.04 you can change locale following these instructions:
   apt update
   apt install locales
   locale-gen en_US.UTF-8
   update-locale LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8
   export LANG="en_US.UTF-8"

You can change system default locale with

dpkg-reconfigure locales

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