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Raspberry Pi

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The Raspberry Pi is an ARM device (BCM2835, ARMv6) with 512 MB RAM (earlier models had 256 MB RAM) and uses an SD(HC) card for storage. This document describes how to install Gentoo on the Raspberry Pi.

A Raspberry Pi running Gentoo

Preparing the SD card

Partitioning

Check that your SD card is compatible: [1]

Create at least two partitions on the card. One FAT32 for the boot partition, and one (with your preferred filesystem) for the root partition:

Example partitioning

Disk /dev/sdb: 16.6 GB, 16574840832 bytes
255 heads, 63 sectors/track, 2015 cylinders, total 32372736 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x1db42224

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *        2048      835379      416666    c  W95 FAT32 (LBA)
/dev/sdb2          835380    31889024    15526822+  83  Linux
/dev/sdb3        31889025    32372735      241855+   5  Extended
/dev/sdb5        31889088    32372735      241824   82  Linux swap / Solaris

For optimal compatibility, it is recommended to use 255H/63S geometry: [2]


Note
SD cards are very different from rotational devices. So it is non-trivial to achieve best I/O-performance, see for example [3] to start understanding the difficulties. Also be aware that there are a lot of contradicting advices regarding partitioning and suitable filesystems for SD cards.

boot

The /boot partition needs the following proprietary firmware files, provided by the Raspberry Pi foundation.

  • bootcode.bin
  • fixup.dat
  • start.elf

If you want to be able to boot the board with the setting gpu_mem=16 in config.txt, you will also need these files:

  • fixup_cd.dat
  • start_cd.elf

Create a file called cmdline.txt containing the necessary kernel parameters. Example:

File/mnt/raspberrypiroot/boot/cmdline.txt

root=/dev/mmcblk0p2 rootdelay=2

These are available as

root # emerge sys-boot/raspberrypi-firmware

Stage 3

Download the appropriate Stage 3:

Extract to the root filesystem on the SD card:

root # tar xfpj stage3-armv6j_hardfp-YYYYMMDD.tar.bz2 -C /mnt/raspberrypiroot/
File/mnt/raspberrypiroot/etc/portage/make.conf

CFLAGS="-O2 -march=armv6j -mfpu=vfp -mfloat-abi=hard"
CXXFLAGS="${CFLAGS}"

Don't forget to adjust fstab (the SD card is recognized as /dev/mmcblk0) and add to /etc/shadow the root password hash generated by:

root # openssl passwd -1

Stage 4

If you'd prefer a self-booting Gentoo tarball (Stage 4), it can be downloaded from here. Please note this image is outdated and unmaintained however


Alternative dd and NOOBS image. The NOOBS image will be created at a daily basis, however the DD image (04/30/2013) is outdated...

You can install NOOBS from here: https://github.com/raspberrypi/noobs and untar the NOOBS image from above in the OS folder (/os/Gentoo).

Portage tree

Download the latest portage tree:

Ensure you have enough inode blocks free on the root partition. Portage takes up approximately 154K.

root # df -ih | egrep 'Mounted|mmc'

Untar portage on the SD card:

root # tar xjvpf portage-latest.tar.bz2 -C /mnt/raspberrypiroot/usr

Compiling the kernel

crossdev

Install sys-devel/crossdev:

root # emerge --ask crossdev

Create a cross toolchain for ARM: (drop -S if you plan to run an unstable system):

root # crossdev -S -v -t armv6j-hardfloat-linux-gnueabi

If you get any errors or portage warnings here, please fix them. It takes a while until the cross toolchain is successfully set up, so go grab a coffee. :-)

Kernel and modules

Download kernel sources for Raspberry Pi from github [4]

root # emerge sys-kernel/raspberrypi-sources

or

root # git clone --depth 1 git://github.com/raspberrypi/linux.git

then configure, compile and install:

root # make ARCH=arm bcmrpi_defconfig
root #
make ARCH=arm CROSS_COMPILE=/usr/bin/armv6j-hardfloat-linux-gnueabi- oldconfig
root #
make ARCH=arm CROSS_COMPILE=/usr/bin/armv6j-hardfloat-linux-gnueabi- -j2
root #
make ARCH=arm CROSS_COMPILE=/usr/bin/armv6j-hardfloat-linux-gnueabi- modules_install INSTALL_MOD_PATH=/mnt/raspberrypiroot/

Create a kernel.img file by

root # emerge sys-boot/raspberrypi-mkimage
root #
imagetool-uncompressed.py arch/arm/boot/Image /mnt/raspberrypiroot/boot/kernel.img

or using the Raspberry Pi mkimage tool from github:

root # chmod a+x imagetool-uncompressed.py
root #
./imagetool-uncompressed.py arch/arm/boot/Image
root #
cp kernel.img /mnt/raspberrypiroot/boot/

That's it! You should all be set now.

Tips and Tricks

  • Storage is rather slow, even with the couple of compatible SDHC class 10 cards. If you want to run emerge on the Raspberry Pi, putting /usr/portage on squashfs will speed up things dramatically.
  • There is no hardware RTC on the Raspberry Pi. Use the ntp-client init script to set correct system time on boot. A fallback incremental clock can be archived by swclock (replaces hwclock).
  • If you require more RAM for Linux, set the option gpu_mem in config.txt. The smallest amount you can set is 16 MB, default is 64 MB [5]
  • More recent, unofficial kernel releases for the Raspberry Pi might be found at Chris Boot's repository: [6]
  • Be sure to test the performance - if your numbers don't match up (for instance in the LINPACK benchmark), something is very wrong.
  • For instructions on how to build binary packages for the Raspberry Pi on an Android phone see this blog post: [7]
  • If you cannot create a working ARM cross-toolchain, a precompiled kernel image is available from the firmware repository. You need to place boot/kernel.img in your boot partition and copy the contents of the modules directory to /lib/modules/ on the SD card.
  • Put the root-fs on a NFS-share and put only the kernel image on SD card (PXE boot client).

Troubleshooting

  • Problem: dmesg is full of smsc95xx 1-1.1:1.0: eth0: kevent 2 may have been dropped and/or page allocation failure messages
    • Solution: Try to update all firmware files in /boot, especially fixup.dat.
    • Solution if the former fails: Add smsc95xx.turbo_mode=N to kernel parameters, or vm.min_free_kbytes = 4096 to /etc/sysctl.conf
  • Problem: the follwing error shows up when running the command
    root # crossdev -S -v -t armv6j-hardfloat-linux-gnueabi
    (...) configure: error: cannot compute suffix of object files: cannot compile (...)

See also

External resources

  • Gentoo Embedded Handbook with more information about embedded hardware, cross compiling and other related topics.
  • Raspberry Pi Hub at eLinux wiki, with more advanced tutorials to get the most out of your Raspberry Pi