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-am625-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
uboot:~# ls mmc 1:1 EFI/ 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 2355 k3-am62-phyboard-lyra-oldi-ac200.dtbo 3222 k3-am62-phyboard-lyra-oldi-ac209a.dtbo 3705 k3-am62-phyboard-lyra-oldi-lcd185.dtbo 2001 k3-am62-phyboard-lyra-vm016-mipi.dtbo 908 k3-am62-phyboard-lyra-x17-spi0.dtbo 60227 k3-am625-phyboard-lyra-rdk.dtb 60227 oftree 300914 tiboot3.bin 1126015 tispl.bin 951955 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
Note
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.