Configuring the Bootloader

Change the Device Tree

By default, U-Boot loads a device tree binary (dtb) file named oftree during boot. The oftree file is a copy of k3-am62a7-phyboard-lyra-rdk.dtb. This portion of the guide will instruct how to change U-boot to load different device trees.

  • Power on the board and press any key to stop autoboot when prompted by the Bootloader.

  • Use the following command to list the available file’s within the boot media’s Boot partition (this is typically where binaries used for boot are stored):

    uboot:~# ls mmc 1:1
    Example Output
    uboot:~# ls mmc 1:1
    21608960   Image
         361   k3-am6-phycore-disable-eth-phy.dtbo
         234   k3-am6-phycore-disable-rtc.dtbo
         235   k3-am6-phycore-disable-spi-nor.dtbo
        1627   k3-am62-phyboard-lyra-gpio-fan.dtbo
        3620   k3-am62-phyboard-lyra-m2-lwb5p.dtbo
        2001   k3-am62-phyboard-lyra-vm016-mipi.dtbo
         908   k3-am62-phyboard-lyra-x17-spi0.dtbo
       59467   k3-am62a7-phyboard-lyra-rdk.dtb
       59467   oftree
      298498   tiboot3.bin
      990887   tispl.bin
      948203   u-boot.img
  • We can check which file is the active device tree like so:

    uboot:~# printenv fdtfile
  • Change the default device tree.

    uboot:~# setenv fdtfile <dtb name>
    uboot:~# saveenv
    uboot:~# boot

U-boot will now load the dtb file named ‘<dtb name>’ automatically during subsequent boots (just replace it with the appropriate file name when you run the command).

Working with Overlays

The PHYTEC BSP also comes with some device tree overlays to help evaluate certain interfaces and accessory hardware. The table “Linux Device Tree Summary in the Release Notes shows an overview of all available overlays.

Enable an Overlay

  • U-boot has an extra environment variable called “overlays” to apply device tree overlay files. We can enable device tree overlays with it like so:

uboot:~# setenv overlays k3-am62-phyboard-lyra-vm016-mipi.dtbo
uboot:~# saveenv
uboot:~# boot
  • Moreover, it’s possible to enable multiple overlays by separating them with a space.

uboot:~# setenv overlays k3-am62-phyboard-lyra-vm016-mipi.dtbo k3-am62-phyboard-lyra-x17-spi0.dtbo
uboot:~# saveenv
uboot:~# boot

The saveenv command stores the boot environment to non-volatile memory. If you would like temporarily adjust the boot environment, you can omit the saveenv command and the boot environment will go back to the previously saved settings on the next boot.

Reset the U-Boot Environment to Default Settings

  • In order to revert the U-Boot environment back to its original settings, run the following:

uboot:~# env default -f -a
uboot:~# saveenv
uboot:~# boot


When booting from the SD card, if you have saved changes to the environment using saveenv, the changes may persist across flashes of the SD card. It is a good idea to default your environment after flashing.