🛠 Boot eMMC/microSD et récupération

Objectives

Cleanly install the ODROID-XU4 system, understand the dual boot between microSD and eMMC module (the eMMC port runs in 8-bit HS400 200 MHz mode under mainline — significantly faster and more durable than an SD card), migrate from one medium to the other, and know how to recover a card that no longer displays anything.

Hardware

• ODROID-XU4, Hardkernel eMMC module (16/32/64 GB) and/or microSD
• eMMC-USB adapter or a second SD card for emergency booting
• Armbian odroidxu4 image (U-Boot mainline, odroid-xu4_defconfig — no proprietary blobs)

Complete code

# 1) Graver l'image Armbian sur la microSD (verifier le disque !)
sudo dd if=Armbian_*_odroidxu4.img of=/dev/sdX bs=4M status=progress oflag=sync

# 2) Amorcé sur SD, copier la SD entiere vers le module eMMC
#    (sdX = carte SD, sdY = module eMMC vu comme disque USB/SD)
sudo dd if=/dev/sdX of=/dev/sdY bs=4M status=progress oflag=sync
sync

# 3) Redemarrer SANS la SD : la carte doit booter sur l'eMMC
sudo poweroff

# 4) Recuperation : carte muette ? Re-graver une image Armbian sur SD,
#    demarrer dessus, puis diagnostiquer ; en dernier recours la console
#    serie ttySAC2 (1,8 V !) affiche le log U-Boot/noyau.
sudo dd if=Armbian_neuve.img of=/dev/sdX bs=4M status=progress oflag=sync

Expected verification

After migration, lsblk shows the root on the eMMC device and dmesg | grep -i mmc mentions HS400 or HS200 mode. Booting without the microSD card works. A recovery dd brings a "dead" SD card back to life.

Common errors

• Writing to the wrong device with dd: always check with lsblk first, as the device name changes when plugging in the eMMC adapter.
• Leaving the SD card in place after migration: the board may boot from it instead of the eMMC.
• Using an arm64 image: the Exynos5422 is ARMv7 32-bit only, use the odroidxu4 image (armhf).
• Staying on an old vendor 3.10 kernel: migrate to Armbian/mainline (4.9 LTS minimum, 6.6.x current).
• Undersized power adapter: require 5 V/4 A, otherwise brownouts and corrupted SD cards.