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-am642-phyboard-electra-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):

Target (U-Boot)

ls mmc 1:1

Example Output

=> ls mmc 1:1
20935168   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-am64-phyboard-electra-gpio-fan.dtbo
    1715   k3-am64-phyboard-electra-pcie-usb2.dtbo
    1224   k3-am64-phyboard-electra-x27-uart3-spi1.dtbo
   60447   k3-am642-phyboard-electra-rdk.dtb
   60447   oftree
  496698   tiboot3.bin
  829315   tispl.bin
  924779   u-boot.img
           System Volume Information/

We can check which file is the active device tree like so:
Target (U-Boot)
```
printenv fdtfile
```
Change the default device tree.
Target (U-Boot)
```
setenv fdtfile <dtb name>
saveenv
reset
```

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:
Target (U-boot)
```
setenv overlays k3-am64-phyboard-electra-rdk-pcie-usb2.dtbo
saveenv
boot
```

Moreover, it’s possible to enable multiple overlays with space separation.

Target (U-boot)

setenv overlays k3-am64-phyboard-electra-rdk-pcie-usb2.dtbo k3-am64-phyboard-electra-rpmsg.dtbo
saveenv
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:
Target (U-boot)
```
env default -f -a
saveenv
boot
```