# eMMC Multi-Boot Setup — Orange Pi 3B

**Status:** Procedural reference. Last verified: 2026-06-02 (discussion with Jez).

## Goal

Boot multiple ARM64 OSes from the OPi 3B's onboard 256GB eMMC, with a u-boot boot menu (`extlinux.conf`) appearing at power-on. No SD card needed after setup.

**Planned OSes:** Orange Pi OS (Arch), Armbian, NixOS

SPI NOR flash was erased via maskrom and is unused going forward.

## Boot Chain (after SPI erase)

```
BootROM → SPI (empty, skip) → microSD (if inserted) → eMMC boot partition → extlinux.conf → menu → kernel
```

If microSD **is** inserted and has a valid bootloader, it takes priority over eMMC. Useful as a lifeboat/rescue path — if eMMC boot breaks, pop in the SD card and you're back.

## Partition Layout

```
mmcblk1 (256GB eMMC)
├── mmcblk1boot0   (hardware boot partition — u-boot SPL + proper)
├── mmcblk1boot1   (unused mirror)
└── mmcblk1
    ├── mmcblk1p1   FAT32   1GB     /boot   (extlinux.conf, kernels, DTBs — shared)
    ├── mmcblk1p2   ext4    85GB    root1   (Orange Pi OS Arch)
    ├── mmcblk1p3   ext4    85GB    root2   (Armbian)
    ├── mmcblk1p4   ext4    ~84GB   root3   (NixOS)
```

### Why a dedicated FAT32 boot partition?

u-boot reads `extlinux.conf` from a FAT, ext4, or btrfs partition. FAT32 is the most universally supported across distro kernel packages. A shared `/boot` means all three OSes drop their kernels and DTBs into one place, and a single `extlinux.conf` controls the menu. 1GB gives headroom for multiple kernel versions across all three OSes.

## Step 1: Clone SD → eMMC (Orange Pi OS, leaves root2/root3 ready)

### 1.1 — Identify devices

Run on the running Orange Pi OS (booted from SD):

```bash
lsblk
mount | grep mmcblk
```

Expected: `mmcblk0` = SD card (boot device), `mmcblk1` = eMMC (target).

### 1.2 — Wipe eMMC partition table

**Destroys everything on eMMC.** Skip if eMMC is already empty.

```bash
sudo sgdisk --zap-all /dev/mmcblk1
sudo blkdiscard /dev/mmcblk1   # optional
```

### 1.3 — Partition eMMC

```bash
sudo gdisk /dev/mmcblk1
```

In `gdisk` interactive mode:

```
o   (new GPT)
n   1   default  +1G    ef00   name=boot
n   2   default  +85G   8300   name=root1
n   3   default  +85G   8300   name=root2
n   4   default  default 8300   name=root3
w   (write, confirm 'y')
```

### 1.4 — Create filesystems

```bash
sudo mkfs.vfat -F 32 -n BOOT /dev/mmcblk1p1
sudo mkfs.ext4 -L root1 /dev/mmcblk1p2
sudo mkfs.ext4 -L root2 /dev/mmcblk1p3
sudo mkfs.ext4 -L root3 /dev/mmcblk1p4
```

### 1.5 — Mount and rsync the live rootfs

```bash
sudo mkdir -p /mnt/root1
sudo mount /dev/mmcblk1p2 /mnt/root1
sudo mkdir -p /mnt/root1/boot
sudo mount /dev/mmcblk1p1 /mnt/root1/boot

sudo rsync -axHAWX --info=progress2 / /mnt/root1/
```

Flags: archive, stay-on-filesystem (critical — skips /proc, /sys, /dev), preserve
hardlinks/ACLs/xattrs, copy whole files (faster locally).

### 1.6 — Bind mount virtual filesystems

```bash
sudo mkdir -p /mnt/root1/{proc,sys,dev,run,tmp}
sudo mount --bind /proc /mnt/root1/proc
sudo mount --bind /sys /mnt/root1/sys
sudo mount --bind /dev /mnt/root1/dev
sudo mount --bind /run /mnt/root1/run
```

### 1.7 — Update fstab

```bash
sudo blkid /dev/mmcblk1p1 /dev/mmcblk1p2
```

Edit `/mnt/root1/etc/fstab`. Replace old SD card references with:

```
UUID=<boot-UUID>  /boot  vfat  defaults,noatime  0  2
UUID=<root1-UUID> /     ext4  defaults,noatime  0  1
```

### 1.8 — Write extlinux.conf

```bash
uname -r
find /mnt/root1/boot -name "*.dtb" | grep orangepi-3b
```

Create `/mnt/root1/boot/extlinux/extlinux.conf`:

```
TIMEOUT 10
DEFAULT orangepi-os

LABEL orangepi-os
    MENU LABEL Orange Pi OS
    LINUX /vmlinuz-<kernel-version>
    INITRD /initrd.img-<kernel-version>
    FDT /dtbs/rockchip/rk3566-orangepi-3b.dtb
    APPEND root=UUID=<root1-UUID> rootwait console=ttyS2,115200 console=tty1
```

### 1.9 — Install u-boot to eMMC hardware boot partition

First check if Orange Pi OS ships u-boot binaries:

```bash
find / -name "idbloader.img" -o -name "u-boot.itb" -o -name "*loader*" 2>/dev/null
```

If files exist at known paths, use them. If not, extract from SD card:

```bash
sudo dd if=/dev/mmcblk0 of=idbloader.img bs=512 count=16384
sudo dd if=/dev/mmcblk0 of=u-boot.itb bs=512 skip=16384 count=8192
```

Write to eMMC hardware boot partition:

```bash
echo 0 | sudo tee /sys/block/mmcblk1/force_ro
sudo mmc bootpart enable 1 1 /dev/mmcblk1
sudo dd if=idbloader.img of=/dev/mmcblk1boot0 bs=512 seek=64
sudo dd if=u-boot.itb of=/dev/mmcblk1boot0 bs=512 seek=16384
sudo sync
```

### 1.10 — Clean up and test

```bash
sudo umount /mnt/root1/boot
sudo umount /mnt/root1/proc /mnt/root1/sys /mnt/root1/dev /mnt/root1/run
sudo umount /mnt/root1
sudo sync
sudo poweroff
```

Remove SD card. Power on. u-boot logo → boot menu → Orange Pi OS from eMMC.

### Troubleshooting

| Symptom | Likely cause | Fix |
|---------|-------------|-----|
| u-boot logo, then blank screen | EDID/HDMI handshake | Add `video=HDMI-A-1:1920x1080@60e` to APPEND line |
| "No bootable device" | u-boot not written to eMMC boot part | Re-do step 1.9 |
| Kernel panic: can't find root | Wrong UUID in extlinux.conf | Boot from SD, mount eMMC, fix UUID |
| Nothing on screen at all | SPI flash interference? HDMI? | Re-check SPI erase, try different monitor |

## Step 2: Install Armbian

(To be documented — Armbian rootfs goes into root2, kernel+DTB added to shared /boot, next LABEL added to extlinux.conf.)

## Step 3: Install NixOS

(To be documented — NixOS rootfs goes into root3. Likely the trickiest since NixOS generates its own /boot structure.)

## Reference

- Rockchip boot flow: <https://opensource.rock-chips.com/wiki_Boot_option>
- U-boot extlinux format: <https://docs.u-boot.org/en/stable/develop/distro.html>
- OPi 3B bring-up: `docs/initial-bringup.md`
- Storage architecture: `docs/storage-architecture.md`