A few months ago, I purchased a Minnowboard MAX to replace a Raspberry Pi that was a bit short on horsepower. It has been running Ubuntu happily, but I decided that it really needed to be running my favorite distro: Gentoo. It took more effort than I expected to get it working, so here are my notes in case anyone else is having trouble (and for my own future reference).

The higher spec Minnowboard MAX has an intel Atom E3825 processor, which is a standard 64 bit x86 processor. One catch with this particular board, however, is that legacy BIOS is not supported. It's UEFI or bust. This isn't a big deal, but it does change the usual Gentoo install process. In particular, I could not get the normal minimal Gentoo install ISO to boot. I ended up using SystemRescueCd to boo the board into a Linux environment. SystemRescueCd is also Gentoo based, so it's trivial to use it as a starting point to install Gentoo.

Initial Boot

As of version 4.1.1, the standard kernel for SystemRescueCd (version 3.10) cannot boo the Minnowboard MAX. Selecting the alternate kernel (version 3.14) does work fine. From here on, the install process is pretty normal. For me, the SD card showed up as /dev/mmcblk0 and my SystemRescueCd USB drive was /dev/sda.

SD Card Partitioning

The following is the partition layout that I used. Note that UEFI requires the boot partition to be formatted with the FAT32 file system.

GNU Parted 3.2
Using /dev/mmcblk0
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) p
Model: SD SD (sd/mmc)
Disk /dev/mmcblk0: 64.8GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:

Number  Start   End     Size    File system     Name    Flags
 1      1049kB  3146kB  2097kB  fat32           grub    bios_grub
 2      3146kB  137MB   134MB   fat16           boot    boot, esp
 3      137MB   2285MB  2147MB  linux-swap(v1)  swap
 4      2285MB  64.8GB  62.5GB  btrfs           rootfs

I did deviate slightly from the standard file system layout in that my boot partition is not mounted at /boot. The boot partition is at /boot/efi. The following is my /etc/fstab file for reference (note that the compress option is specific to btrfs).

/dev/mmcblk0p2      /boot/efi       vfat    defaults,noatime        1 2
/dev/mmcblk0p3      none            swap    sw                      0 0
/dev/mmcblk0p4      /               btrfs   compress,noatime        0 1

Setting make.conf

When configuring /etc/portage/make.conf, add the following line to make installing GRUB easier:

GRUB_PLATFORMS="efi-64"

Otherwise, you'll get errors when trying to install GRUB to the SD card later.

Configuring GRUB

This turned out to be the hardest part of the install. Every time I booted the board after installing everything, I'd get a kernel panic saying that the root file system device didn't exist. I assumed this was due to missing a driver in the kernel, but nothing worked. I even tried using the same kernel configuration as SystemRescueCd with an initramfs, which obviously could boot correctly since I used it for the install, but still got the same kernel panic. After hours of searching, with trial and error, I came across this Gentoo forums post regarding a similar embedded board. The point mentioned in that post is to tell GRUB to add a delay.

It seems that the kernel is loading too fast and the SD card is not yet initialized when the kernel attempts to mount the root file system. The solution mentioned in the post is to add a delay to GRUB. After emerging GRUB, edit the file /etc/default/grub and add the line rootdelay=8 to the GRUB_CMDLINE_LINUX_DEFAULT option. Then continue with installing GRUB to the SD card.

GRUB_CMDLINE_LINUX_DEFAULT="rootdelay=8"

The choice of eight seconds is arbitrary and I'm sure a lower value could be used with some experimentation.

With Gentoo up and running, I'm quite impressed with the performance of the dual core Minnowboard MAX. It's usually faster than the old Athlon 64 2600+ I used for experimentation.