Raspberry Pi

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Note
Since the Raspberry Pi hardware and setup process has not changed much over the years, this article supports both the Rpi 1 and the Rpi 2. The Rpi3 is supported in 32-bit mode via the Rpi 2 process.
For Rpi3 in 64-bit mode see Raspberry Pi 3 64 bit Install. An (unofficial) bootable 64-bit Gentoo image for the RPi3 is also available; please see below for further details.

This document describes how to install Gentoo on the Raspberry Pi 1, 2, and 3 in 32-bit mode.

The Raspberry Pi is series of single-board computers based on ARM devices. Raspberry Pi 1 is based on BCM2835 SoC and features a single core CPU (ARMv6), with 512 MB RAM. Earlier models had 256 MB RAM.
Chithanh 's Raspberry Pi 1 running Gentoo
Raspberry Pi 2 is based on BCM2836 SoC and features a quad-core CPU (ARMv7) and 1 GB RAM. The model 1 uses an SD card for storage but the model 2 uses a microSD. All versions have a VideoCore IV GPU.
Raspberry Pi 3 B is based on BCM2837 SoC. According to #gentoo-arm, although the ARMv8 CPU in the Raspberry Pi 3 B is 64-bit, almost everything else is 32-bit, and therefore only 32-bit kernels are supplied from upstream for the machine.[1] Those who want to build a 32-bit kernel for the Pi 3 B, follow the Raspberry Pi 2 options listed below. 64 bit kernels are covered in the Raspberry Pi 3 64 bit Install guide.
Zucca 's RaspberryPi 3 B with heatsinks
Raspberry Pi Zero is small size single-board computer using same ARM MCB2835 SoC as Raspberry Pi. Versions 1.3 and above have camera connector compatible with other Raspberry Pi cameras modules and W version has integrated WiFi module. It has 512 MB RAM and out-of-box possibility to run at 1 GHz.

Installation

Partitioning

The SD card must be properly prepared before installing Gentoo. Before partitioning, check to see if the SD card is listed as compatible in this list.

Create at least two partitions on the SD card. The /boot partition should be FAT32. The root (/ partition can be any preferred Linux filesystem, however since SD cards are flash-based media, there are many benefits to using F2FS.

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, 255H/63S geometry is recommended.

Note
SD cards are very different from rotational devices. So it is non-trivial to achieve best I/O-performance. See example [1] to start understanding the difficulties. Also, be aware that there are a lot of contradicting advice regarding partitioning and suitable filesystems for SD cards.

Boot partition

The minimum setup for a correct /boot partition requires the following proprietary firmware files, provided by the Raspberry Pi foundation:

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


To boot the Raspberry Pi with gpu_mem=16 setting in config.txt, following files are required:

  • fixup_cd.dat
  • start_cd.elf


There are two video drivers for the Pi. The older one uses a fixed reserved GPU memory space. The Open Source VC4 driver uses the kernels contiguous memory allocator. Set gpu_mem=16 when you use the vc4 driver to avoid wasting RAM.

The proprietary firmware files are just an emerge away:

root #emerge --ask sys-boot/raspberrypi-firmware
Note
The firmware files are installed in /boot. The boot partition of the SD card should be mounted on /boot before emerging the sys-boot/raspberrypi-firmware package.

If you are planning to use a custom kernel, emerge the live ebuild =sys-boot/raspberrypi-firmware-9999. This will install latest firmware directly from the repository of the RaspberryPi foundation and will not install a kernel or modules.

The firmware ebuild created a file called cmdline.txt which specifeis any necessary kernel parameters. Make sure you adjust your root partition, if necessary. For example change the root parameter to:

FILE /mnt/raspberrypiroot/boot/cmdline.txt
root=/dev/mmcblk0p2 rootdelay=2

When the file /boot/config.txt does not exist, bootcode.bin defaults to sensible settings for most things

On a Pi 1 the kernel is expected to be called kernel.img
On a Pi 2 the kernel is expected to be called kernel7.img
On a Pi 3 if kernel8.img exists, the Pi is put into 64 bit mode and kernel8.img is booted.
else kernel7.img is booted.

Stage 3

Download appropriate Stage 3 tarball.

For Raspberry Pi A, A+, B, B+:

For the Raspberry Pi 2 or a Raspberry Pi 3 running in 32-bit mode:

Extract the root filesystem to SD card:

For the Raspberry Pi A, A+, B, B+:

root #tar xpjf stage3-armv6j_hardfp-YYYYMMDD.tar.bz2 -C /mnt/raspberrypiroot/

For the Raspberry Pi 2 or Raspberry Pi 3 running in 32-bit mode:

root #tar xpjf stage3-armv7a_hardfp-YYYYMMDD.tar.bz2 -C /mnt/raspberrypiroot/


Adjust the make.conf file:

FILE /mnt/raspberrypiroot/etc/portage/make.conf
# Raspberry Pi A, A+, B, B+:
CFLAGS="-O2 -march=armv6j -mfpu=vfp -mfloat-abi=hard"
CXXFLAGS="${CFLAGS}"

# Raspberry Pi 2, or Raspberry Pi 3 running in 32 bit mode:
CFLAGS="-O2 -march=armv7-a -mfpu=neon-vfpv4 -mfloat-abi=hard"
CXXFLAGS="${CFLAGS}"


Do not forget to adjust the fstab file. The SD card is recognized as /dev/mmcblk0).

Generate the root password hash:

root #openssl passwd -1

Add the hash to the /etc/shadow file.

Stage 4

There is also an option of a self-booting Gentoo tarball (Stage 4), it can be downloaded from here. Please note this image appears to be outdated and unmaintained

NOOBS image. The NOOBS image will be created on a daily basis. I'd be pleased to get feedback...

NOOBS images can be downloaded from here: https://github.com/raspberrypi/noobs, then untar the NOOBS image from above in the OS directory (/os/Gentoo).

Portage tree

Download the latest Portage tree:

Ensure there are enough inode blocks free on the root partition. Portage takes up approximately 181K inodes.

root #df -ih | grep -E 'Mounted|mmc'

Extract Portage to the SD card:

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

Cross compiling

To aid the Raspberry Pi's low power processor and hasten the Gentoo installation process, adding another machine to help the Rpi with compile jobs is preferred. Gentoo developers have created a cross compiling tool called crossdev in order to assist with toolchain generation. Once the toolchain is generated on a stronger machine, the stronger machine can help with compilation tasks, which saves much time.

Crossdev

Install the sys-devel/crossdev wrapper scripts:

root #emerge --ask sys-devel/crossdev

Create the cross toolchain for ARM, specifying the correct CPU architecture for the device as follows.

Note
The -S option can be omitted for those who wish to run an unstable or absolute bleeding-edge latest system.

For the Raspberry Pi A, A+, B, B+:

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

For the Raspberry Pi 2 or Raspberry Pi 3 B in 32-bit mode (recommended):

root #crossdev -S -v -t armv7a-hardfloat-linux-gnueabi

For the Raspberry Pi 3 B in 64-bit mode:

root #crossdev -S -v -t aarch64-unknown-linux-gnu --genv 'USE="cxx multilib fortran -mudflap nls openmp -sanitize"'
root #cd /usr/aarch64-unknown-linux-gnu/etc/portage && rm make.profile && ln -s /usr/portage/profiles/default/linux/arm64/13.0/desktop make.profile
Note
This will ensure a compile even if the host system is hardened, ie. defaults to sanitize (which does not yet work on arm64 architecture). A multilib profile may need toggled.

If there are any errors or Portage warnings here, please fix them. It will take a while for the cross toolchain to be successfully built. Go grab a coffee!

Compiling using chroot

It is possible to use generic x86_64 or i386 PC to chroot into existing SD card with RaspberryPi system. This approach is significantly faster than compilation on RaspberryPi (in case of using modern 4 core CPUs it gives about half of 'native' performance) and is slower (but easier) than using cross compiling approach.

To do so static installation of app-emulation/qemu is needed. After emerging QEMU with `static-user` USE flag qemu-arm executable needs to be copied into chrooting system:

root # cd /mnt/rpi
root # ROOT=$PWD/ emerge --usepkgonly --oneshot --nodeps qemu

Once done it is necessary to register ARM executables interpretatior in running kernel:

root # echo ':arm:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/bin/qemu-arm:' > /proc/sys/fs/binfmt_misc/register

Before chrooting add necessary mounts to slave system:

root #mount /dev/mmcblk0p1 /mnt/rpi/boot
root #mount -o bind /dev /mnt/rpi/dev
root #mount -o bind /proc /mnt/rpi/proc
root #mount -o bind /sys /mnt/rpi/sys
root #mount -o rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000 devpts /mnt/rpi/dev/pts -t devpts

Finally you can chroot into RaspberryPi system:

root #chroot /mnt/rpi

Kernel and modules

Download kernel sources for Raspberry Pi from GitHub [2]

root #emerge --ask sys-kernel/raspberrypi-sources

Alternatively, to get the 'bleeding edge' Raspberry Pi kernel sources:

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

Manual compilation

Configure and install kernel manually:

For the Raspberry Pi A, A+, B, B+:

root #make ARCH=arm bcmrpi_defconfig
root #make ARCH=arm CROSS_COMPILE=armv6j-hardfloat-linux-gnueabi- oldconfig
root #make ARCH=arm CROSS_COMPILE=armv6j-hardfloat-linux-gnueabi- -j$(nproc)
root #make ARCH=arm CROSS_COMPILE=armv6j-hardfloat-linux-gnueabi- modules_install INSTALL_MOD_PATH=/mnt/raspberrypiroot/

For the Raspberry Pi 2 or Raspberry Pi 3 B in 32-bit mode (recommended):

root #make ARCH=arm bcm2709_defconfig
root #make ARCH=arm CROSS_COMPILE=armv7a-hardfloat-linux-gnueabi- oldconfig
root #make ARCH=arm CROSS_COMPILE=armv7a-hardfloat-linux-gnueabi- -j$(nproc)
root #make ARCH=arm CROSS_COMPILE=armv7a-hardfloat-linux-gnueabi- modules_install INSTALL_MOD_PATH=/mnt/raspberrypiroot/

Alternatively, use the following command to configure the kernel manually:

root #make ARCH=arm menuconfig

Genkernel

genkernel can be used to cross-compile the kernel for Raspberry Pi. With genkernel all the preferences can be saved in genkernel.conf file for later use. The values of these variables need to be changed in /etc/genkernel-rpi.conf:

FILE /etc/genkernel-rpi.conf
# install kernel manually
INSTALL="no"

# Set arch to arm
ARCH_OVERRIDE="arm"

# No need to mount BOOTDIR and make symlink as the kernel is
# installed manually
MOUNTBOOT="no"
SYMLINK="no"

# Adjust this as needed for the machine.
MAKEOPTS="-j3"

# For Raspberry Pi A, A+, B, B+
UTILS_CROSS_COMPILE="armv6j-hardfloat-linux-gnueabi-"
KERNEL_CROSS_COMPILE="armv6j-hardfloat-linux-gnueabi-"

# For Raspberry Pi 2, or Raspberry Pi 3 B in 32-bit mode
UTILS_CROSS_COMPILE="armv7a-hardfloat-linux-gnueabi-"
KERNEL_CROSS_COMPILE="armv7a-hardfloat-linux-gnueabi-"

# Change this to the path of raspberrypi linux kernel sources.
# It is possible to make this a symlink pointing to the
# /usr/src/linux-rpi like it's done with a normal kernel.
# For example: ln -s /usr/src/linux-3.6.11-raspberrypi /usr/src/linux-rpi
DEFAULT_KERNEL_SOURCE="/usr/src/linux-rpi"

# Point this variable to the directory where the SD card is mounted.
# Note that the location needs to be mounted manually before running genkernel.
INSTALL_MOD_PATH="/mnt/raspberrypiroot"

After saving the configuration file (for example to /etc/genkernel-rpi.conf), mount the RaspberryPi SD card to the INSTALL_MOD_PATH configured above. Assuming the Raspberry Pi root partition device is /dev/sdd3, run:

root #mount /dev/sdd3 /mnt/raspberrypiroot

Now execute genkernel. For the Raspberry Pi A, A+, B, B+:

root #ARCH=arm genkernel --config=/etc/genkernel-rpi.conf --kernel-config=/usr/src/linux-rpi/arch/arm/configs/bcmrpi_defconfig kernel

For the Raspberry Pi 2 or Raspberry Pi 3 B in 32-bit mode (recommended):

root #ARCH=arm genkernel --config=/etc/genkernel-rpi2.conf --kernel-config=/usr/src/linux-rpi/arch/arm/configs/bcm2709_defconfig kernel

Save the above command to the custom script:

FILE /usr/local/bin/genkernel-rpi.sh
#!/bin/sh
ARCH=arm genkernel --config=/etc/genkernel-rpi2.conf --kernel-config=/usr/src/linux-rpi/arch/arm/configs/bcm2709_defconfig kernel
root #chmod +x /usr/local/bin/genkernel-rpi.sh

Now simply create kernel for the Raspberry Pi by executing:

root #genkernel-rpi.sh

Installing kernel image

For Raspberry Pi A, B, B+ (not 2 B!) create a kernel.img file by:

root #cp arch/arm/boot/Image /mnt/raspberrypiroot/boot/kernel.img

If your Raspberry Pi does not boot with this kernel, you may have an older firmware, which requires kernel to be uncompressed. If so, you will need to:

root #emerge --ask 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/

Alternatively, some devices need the zImage to be processed using the mkknlimg script. To do this:

root #scripts/mkknlimg arch/arm/boot/zImage /mnt/raspberrypiroot/boot/kernel.img

For Raspberry Pi 2 B just copy arch/arm/boot/zImage to /boot/kernel7.img:

root #cp arch/arm/boot/zImage /mnt/raspberrypiroot/boot/kernel7.img

Copy the updated device tree binaries (.dtb) and device tree overlay (.dto) files into the boot partition:

root #cp arch/arm/boot/dts/*.dtb /mnt/raspberrypiroot/boot/
root #cp arch/arm/boot/dts/overlays/* /mnt/raspberrypiroot/boot/overlays/
Note
The device tree files describe the hardware to the kernel. They are a part of the kernel on all arm systems
Note
Copying the dtb files was necessary for me to get the official Raspberry Pi 7" touchscreen (input device) working.

That's it!

RPi3 Specific

WiFi

RPi3 builtin WiFi driver brcmfmac requires binary firmware blob brcmfmac43430-sdio.bin and it's configuration brcmfmac43430-sdio.txt to work properly [3]. These can be found in firmware-nonfree repository. If these files are missing on Your system:

root #mkdir /lib/firmware/brcm/
root #cp firmware-nonfree/brcm80211/brcm/brcmfmac43430-sdio.* /lib/firmware/brcm/

Bluetooth

RPi3 builtin BlueTooth driver requires BCM43430A1.hcd binary blob[4] in /etc/firmware folder to work properly. This file can be found in OpenELEC/misc-firmware or ArchLinux AUR repository [5]. Once downloaded BCM43430A1.hcd should be copied to /etc/firmware.

root #mkdir /etc/firmware
root #cp pi-bluetooth/BCM43430A1.hcd /etc/firmware

The following needs to be done every time the system boots:

root #btattach -N -B /dev/ttyAMA0 -P bcm -S 921600

Alternatively, if using bluez built with the "deprecated" use flag, you can use the older approach:

root #hciattach /dev/ttyAMA0 bcm43xx 921600 noflow -


Note
You may need to repeat the above command if it fails. There is patched hciattach version in Archlinux AUR repository available, it may work more reliably[6].

Serial

Serial port on RPi3 has some issues related to variable clock rate[7][8]. A few workarounds/solutions are available.

Bootable 64-bit Gentoo Image for RPi3

Screenshot of RPi3 running 64-bit Gentoo image (Xfce)

Those interested in trying 64-bit Gentoo on their RPi3 may wish to check out the (unofficial) bootable image available here, from which the above screenshot has been taken (see also this forum thread).

Leveraging recently improved 64-bit support in the official Raspberry Pi kernel tree, the image supports:

  • The Pi's onboard Ethernet, WiFi and Bluetooth adaptors;
  • ALSA sound playback, via headphone jack and HDMI
  • Accelerated VC4 graphics, via vc4-fkms-v3d / vc4 kernel module / Mesa.

The image contains a full Portage tree (and /etc/portage/<...> set) so that you can run emerge operations immediately.

The project's GitHub page additionally contains instructions for setting up crossdev and distcc to build for the 64-bit RPi3.

VideoCore4

To enable VideoCore4 GPU acceleration on RPi device add following to /boot/config.txt:

FILE /boot/config.txt
dtoverlay=vc4-kms-v3d,cma-128

Also you need live raspberrypi-firmware-9999 ebuild to be installed (as others seems to be outdated and not compatible with latest kernels).

Finaly, add VideoCore4 configuration to mesa and rebuild it.

FILE /etc/portage/make.conf
VIDEO_CARDS="vc4"

For more info refer to Raspberry Pi VideoCore4 page.

Tips and tricks

  • Storage is rather slow, even with the couple of compatible SDHC class 10 cards. If emerge will be running 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 service to set the correct system time on boot. A fallback incremental clock can be archived by the swclock service (replaces the hwclock service).
  • If more RAM is required for Linux, set the option gpu_mem in config.txt. The smallest amount that can be set is 16 MB, default is 64 MB [9]
  • More recent, unofficial kernel releases for the Raspberry Pi might be found at Chris Boot's repository: [10]
  • Be sure to test the performance - if the 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: [11]
  • If it is not possible to create a working ARM cross-toolchain, a precompiled kernel image is available from the firmware repository. The boot/kernel.img needs to be places in the boot partition and the contents of the modules directory copied 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 following 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 (...)
    • Solution: Try the following command instead[2]:
      root #CFLAGS="-O2 -pipe -march=armv6j -mfpu=vfp -mfloat-abi=hard" crossdev --stage3 -S -v -t armv6j-hardfloat-linux-gnueabi
  • Problem: On-board audio is inaccessible / non-functional.
    • Solution: Ensure that your /boot/config.txt contains the line dtparam=audio=on, then reboot. Ensure that the PCM channel is unmuted.

See also

External resources

Books

References