This is the documentation for the latest (main) development branch of Zephyr. If you are looking for the documentation of previous releases, use the drop-down menu on the left and select the desired version.

UP Squared


UP² (UP Squared) is an ultra compact single board computer with high performance and low power consumption. It features the latest Intel® Apollo Lake Celeron™ and Pentium™ Processors with only 4W of Scenario Design Power and a powerful and flexible Intel® FPGA Altera MAX 10 onboard.

UP Squared

Up Squared (Credit:

This board configuration enables kernel support for the UP Squared board.


This board configuration works on all three variants of UP Squared boards containing Intel® Pentium™ SoC, Intel® Celeron™ SoC, or Intel® Atom™ SoC.


General information about the board can be found at the UP Squared website.

Supported Features

In addition to the standard architecture devices (HPET, local and I/O APICs, etc.), Zephyr supports the following Apollo Lake-specific SoC devices:


  • GPIO

  • I2C

HSUART High-Speed Serial Port Support

The Apollo Lake UARTs are NS16550-compatible, with “high-speed” capability.

Baud rates beyond 115.2kbps (up to 3.6864Mbps) are supported, with additional configuration. The UARTs are fed a master clock which is fed into a PLL which in turn outputs the baud master clock. The PLL is controlled by a per-UART 32-bit register called PRV_CLOCK_PARAMS (aka the PCP), the format of which is:









The resulting baud master clock frequency is (n/m) * master.

Typically, the master clock is 100MHz, and the firmware by default sets the PCP to 0x3d090240, i.e., n = 288, m =  15625, which results in the de-facto standard 1.8432MHz master clock and a max baud rate of 115.2k. Higher baud rates are enabled by changing the PCP and telling Zephyr what the resulting master clock is.

Use devicetree to set the value of the PRV_CLOCK_PARAMS register in the UART block of interest. Typically a devicetree overlay file would be present in the application directory (specific to the board, such as up_squared.overlay), with contents like this:

/ {
    soc {
        uart@0 {
            pcp = <0x3d090900>;
            clock-frequency = <7372800>;
            current-speed = <230400>;

The relevant variables are pcp (the value to use for PRV_CLOCK_PARAMS), and clock-frequency (the resulting baud master clock). The meaning of current-speed is unchanged, and as usual indicates the initial baud rate.


GPIOs are exposed through the HAT header, and can be referred using predefined macros such as UP2_HAT_PIN3. The physical pins are connected to the on-board FPGA acting as level shifter. Therefore, to actually utilize these GPIO pins, the function of the pins and directions (input/output) must be set in the BIOS. This can be accomplished in BIOS, under menu Advanced, and option HAT Configurations. When a corresponding pin is set to act as GPIO, there is an option to set the direction of the pin. This needs to be set accordingly for the GPIO to function properly.

Connections and IOs

Refer to the UP Squared website and UP Squared Pinout website for connection diagrams.

Programming and Debugging

Use the following procedures for booting an image on a UP Squared board.

Build Zephyr application

  1. Build a Zephyr application; for instance, to build the hello_world application on UP Squared:

    # From the root of the zephyr repository
    west build -b up_squared samples/hello_world


    A Zephyr EFI image file named zephyr.efi is automatically created in the build directory after the application is built.

Preparing the Boot Device

Prepare a USB flash drive to boot the Zephyr application image on a UP Squared board.

  1. Refer to the UP Squared Serial Console Wiki page for instructions on how to connect for serial console.

  2. Format the USB flash drive as FAT32.

    On Windows, open File Explorer, and right-click on the USB flash drive. Select Format.... Make sure in File System, FAT32 is selected. Click on the Format button and wait for it to finish.

    On Linux, graphical utilities such as gparted can be used to format the USB flash drive as FAT32. Alternatively, under terminal, find out the corresponding device node for the USB flash drive (for example, /dev/sdd). Execute the following command:

    $ mkfs.vfat -F 32 <device-node>


    Make sure the device node is the actual device node for the USB flash drive. Or else you may erase other storage devices on your system, and will render the system unusable afterwards.

  3. Copy the Zephyr EFI image file zephyr/zephyr.efi to the USB drive.

Booting the UP Squared Board

Boot the UP Squared board to the EFI shell with USB flash drive connected.

  1. Insert the prepared boot device (USB flash drive) into the UP Squared board.

  2. Connect the board to the host system using the serial cable and configure your host system to watch for serial data. See


    On Windows, PuTTY has an option to set up configuration for serial data. Use a baud rate of 115200.

  3. Power on the UP Squared board.

  4. When the following output appears, press F7:

    Press <DEL> or <ESC> to enter setup.
  5. From the menu that appears, select the menu entry that describes that particular EFI shell.

  6. From the EFI shell select Zephyr EFI image to boot.

    Shell> fs0:zephyr.efi


    You can safely ignore this message if it appears:

    WARNING: no console will be available to OS

Booting the UP Squared Board over network

Build Zephyr image

  1. Follow Build Zephyr application steps to build Zephyr image.

Prepare Linux host

  1. Install DHCP, TFTP servers. For example dnsmasq

    $ sudo apt-get install dnsmasq
  2. Configure DHCP server. Configuration for dnsmasq is below:

    # Only listen to this interface
  3. Configure TFTP server.

    # tftp

    zephyr.efi is a Zephyr EFI binary created above.

  4. Copy the Zephyr EFI image zephyr/zephyr.efi to the /srv/tftp folder.

    $ sudo cp zephyr/zephyr.efi /srv/tftp
  5. TFTP root should be looking like:

    $ tree /srv/tftp
    └── zephyr.efi
  6. Restart dnsmasq service:

    $ sudo systemctl restart dnsmasq.service

Prepare UP Squared board for network boot

  1. Enable PXE network from BIOS settings.

    Advanced -> Network Stack Configuration -> Enable Network Stack -> Enable Ipv4 PXE Support
  2. Make network boot as the first boot option.

    Boot -> Boot Option #1 : [Network]

Booting UP Squared

  1. Connect the board to the host system using the serial cable and configure your host system to watch for serial data. See

  2. Power on the UP Squared board.

  3. Verify that the board got an IP address:

    $ journalctl -f -u dnsmasq
    dnsmasq-dhcp[5386]: DHCPDISCOVER(eno2) 00:07:32:52:25:88
    dnsmasq-dhcp[5386]: DHCPOFFER(eno2) 00:07:32:52:25:88
    dnsmasq-dhcp[5386]: DHCPREQUEST(eno2) 00:07:32:52:25:88
    dnsmasq-dhcp[5386]: DHCPACK(eno2) 00:07:32:52:25:88
  4. Verify that network booting is started:

    $ journalctl -f -u dnsmasq
    dnsmasq-tftp[5386]: sent /srv/tftp/zephyr.efi to
  5. When the boot process completes, you have finished booting the Zephyr application image.