U-Boot and Boot Configuration

WendyOS on Raspberry Pi does not use U-Boot. The RPi firmware chain (bootcode.bin / EEPROM on RPi 5, bootcode.bin on RPi 4) loads the kernel directly from the FAT32 /boot partition using config.txt and cmdline.txt.

This document covers that boot configuration: where the files live, what WendyOS sets, and how to customise them.

Boot files on the /boot partition

config.txt

WendyOS sets the following in config.txt via the rpi-config_%.bbappend recipe:

# UART
enable_uart=1

# RPi 4: standard uart0 overlay
dtoverlay=uart0

# RPi 5: Pi5-specific overlay (uart0-pi5)
dtoverlay=uart0-pi5

# USB gadget mode (added when ENABLE_DWC2_PERIPHERAL=1)
dtoverlay=dwc2

# PCIe x1 lane (RPi 5 only, for NVMe access)
dtparam=pciex1

Additional machine-level settings (from raspberrypi5-wendyos.conf / raspberrypi4-64-wendyos.conf):

You can add your own entries to config.txt in two ways:

1. At build time — set RPI_EXTRA_CONFIG in local.conf:

   RPI_EXTRA_CONFIG = "dtparam=i2c_arm=on\n"

2. At runtime — mount the /boot partition and edit config.txt directly, then reboot.

cmdline.txt

The kernel command line is assembled by meta-raspberrypi from several sources. WendyOS appends:

console=tty1

The root partition is identified differently depending on the board:

• RPi 4 and 5 (GPT layout): root=PARTUUID=<uuid> — a stable UUIDv4 assigned at build time.
• RPi 3 (MBR layout): root=LABEL=root — the filesystem label set in rpi-mbr.wks. Under MBR, the kernel exposes PARTUUIDs as <disk-signature>-<partno>, not as UUIDv4, so PARTUUID references would not resolve.

The full command line on a typical RPi 5 WendyOS device looks like:

console=serial0,115200 console=tty1 root=PARTUUID=<uuid> rootfstype=ext4 rootwait

On RPi 3:

console=serial0,115200 console=tty1 root=LABEL=root rootfstype=ext4 rootwait

To add additional kernel parameters at build time, set CMDLINE:append in your layer or local.conf:

CMDLINE:append = " your.param=value"

Boot order (RPi 5 EEPROM)

On RPi 5, boot order and PCIe probe are stored in the EEPROM, not in config.txt. WendyOS manages two EEPROM settings automatically via one-shot systemd services:

BOOT_ORDER=0xf461 means (right-to-left nibbles): SD card (1) → NVMe (6) → Network (4) → restart (f).

Both services are guarded by flag files (/var/lib/wendyos/eeprom-updated, /var/lib/wendyos/eeprom-nvme-updated) so they run at most once per device. If an update is needed, the service stages it with rpi-eeprom-update and reboots.

See eeprom.md for full details on reading and writing EEPROM settings.

Reading current boot configuration

# View current config.txt
cat /boot/config.txt

# View kernel command line that was used for this boot
cat /proc/cmdline

# RPi 5: read current EEPROM configuration
rpi-eeprom-config

Customising at runtime

The /boot partition is writable. After editing, reboot to pick up changes.

# Remount read-write if necessary
mount -o remount,rw /boot

# Edit
nano /boot/config.txt

# Sync and reboot
sync && reboot

Note: OTA updates on Jetson/Tegra machines use Mender and replace the entire rootfs, but the /boot partition and /config partition sit outside the update boundary and are not affected by updates.