# Raspberry Pi

Raspberry Pi (RPi) is a minimalist computer built for the ARMv6 architecture. More information about this project and technical specification.

## Article preface

This article is not meant to be an exhaustive setup guide and assumes that the reader has setup an Arch system before. Arch newbies are encouraged to read the Beginners' guide if unsure how to preform standard tasks such as creating users, managing the system, etc.

Note: Support for the ARM architecture is provided on http://archlinuxarm.org not through posts to the official Arch Linux Forum. Any posts related to ARM specific issues will be promptly closed per the Arch Linux Distribution Support ONLY policy.

## Installing Arch Linux ARM

See the Arch Linux ARM documentation.

### Resize filesystem

The image size is 2GB. In order to expand the root filesystem to use the whole SD card (assuming it is bigger than 2GB), please follow some of the existing guides.

## Wlan

By default a fresh install will connect to a connected LAN with dhcpcd. If you want to access your Raspberry Pi via wlan from the start, create the necessary files on the sdcard. You need a netctl profile and enable the systemd unit netctl-auto.

- Mount the sdcard-partition5

    # mount /dev/mmcblk0p5 /mnt

- Create a netctl profile, if you use netctl on your main machine, you can just copy one

    # cp /etc/netctl/profilename /mnt/etc/netctl/

or you can adapt one from the /examples directory `/etc/netctl/examples`. Make sure the profile uses interface `wlan0` not `wlpsXsX`.

- To automatically connect to an available network enable the systemd unit netctl-auto.

    # ln -s /usr/lib/systemd/system/netctl-auto@.service /mnt/etc/systemd/system/multi-user.target.wants/netctl-auto@wlan0.service

- Unmount the sdcard

    # umount /mnt

- Insert it in your rpi and boot it.
- Connect with `ssh root@alarmpi` password is `root`

## Audio

Note: The requisite module `snd-bcm2835` should be autoloaded by default.

Install the alsa-utils, alsa-firmware, alsa-lib and alsa-plugins packages:

    # pacman -S alsa-utils alsa-firmware alsa-lib alsa-plugins

Optionally adjust the default volume using `alsamixer` and ensure that the sole source "PCM" is not muted (denoted by `MM` if muted, press `M` to unmute).

Select an audio source for output:

    $ amixer cset numid=3 x

Where `x` corresponds to:

- 0 for Auto
- 1 for Analog out
- 3 for HDMI

### Caveats for HDMI audio

Some applications require a setting in `/boot/config.txt` to force audio over HDMI:

    hdmi_drive=2

## Video

### HDMI / analog TV-Out

To turn the HDMI or analog TV-Out on or off, have a look at

    /opt/vc/bin/tvservice

Use the -s parameter to check the status of your display, the -o parameter to turn your display off and -p parameter to power on HDMI with preferred settings.

Adjustments are likely required to correct proper overscan/underscan and are easily achieved in `boot/config.txt` in which many tweaks are set. To fix, simply uncomment the corresponding lines and setup per the commented instructions:

    # uncomment the following to adjust overscan. Use positive numbers if console
    # goes off screen, and negative if there is too much border
    #overscan_left=16
    overscan_right=8
    overscan_top=-16
    overscan_bottom=-16

Users wishing to use the analog video out should consult this config file which contains options for non-NTSC outputs.

A reboot is needed for new settings to take effect.

### X.org driver

The X.org driver for Raspberry Pi can be installed with the xf86-video-fbdev package:

    # pacman -S xf86-video-fbdev

## Onboard hardware sensors

### Temperature

Temperatures sensors can be queried with utils in the raspberrypi-firmware-tools package. The RPi offers a sensor on the BCM2835 SoC (CPU/GPU):

    $ /opt/vc/bin/vcgencmd measure_temp

    temp=49.8'C

Alternatively, simply read from the file system:

    $ cat /sys/class/thermal/thermal_zone0/temp

    49768

For human readable output:

    awk '{printf "%3.1f°C\n", $1/1000}' /sys/class/thermal/thermal_zone0/temp

    54.1°C

### Voltage

Four different voltages can be monitored via `/opt/vc/bin/vcgencmd` as well:

    $ /opt/vc/bin/vcgencmd measure_volts <id>

Where `<id>` is:

- core for core voltage
- sdram_c for sdram Core voltage
- sdram_i for sdram I/O voltage
- sdram_p for sdram PHY voltage

### Lightweight Monitoring Suite

monitorix has specific support for the RPi since v3.2.0. Screenshots available here.

## Overclocking/underclocking

The RPi can be overclocked by editing `/boot/config.txt`, for example:

    arm_freq=800
    arm_freq_min=100
    core_freq=300
    core_freq_min=75
    sdram_freq=400
    over_voltage=0

The optional xxx_min lines define the min usage of their respective settings. When the system is not under load, the values will drop down to those specified. Consult the Overclocking article on elinux for additional options and examples.

A reboot is needed for new settings to take effect.

Note: The overclocked setting for CPU clock applies only when the governor throttles up the CPU, i.e. under load.

Users may query the current frequency of the CPU via this command:

    $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq

## Tips for maximizing SD card performance

See Maximizing performance for the general performance improvements.

### Enable fsck on boot

To enable fsck on boot, the root filesystem should be mounted as readonly first, and then remounted as read-writable.

First, make root as read-only on boot. edit `/boot/cmdline.txt` to add "ro" after the option indicating root partition.

    ipv6.disable=1 selinux=0 plymouth.enable=0 dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p5 ro rootfstype=ext4 elevator=noop rootwait

Next, add next line in `/etc/fstab` to remount the partition during boot.

    /dev/mmcblk0p5  /       ext4    remount,rw        0       0

### Move /var/log to RAM

Warning: All system logs will be lost on every reboot.

Add this entry to your `/etc/fstab` to create a RAM disk that is 16MiB in size:

    tmpfs   /var/log        tmpfs   nodev,nosuid,size=16M   0       0

Delete your existing log directory:

    # rm -R /var/log

Reboot system for changes to take effect.

## Serial console

Edit the default `/boot/cmdline.txt`, change `loglevel` to `5` to see boot messages:

    loglevel=5

Change speed from 115200 to 38400:

    console=ttyAMA0,38400 kgdboc=ttyAMA0,38400

Start getty service

    # systemctl start getty@ttyAMA0

Enable on boot

    # systemctl enable getty@ttyAMA0.service

Creating the proper service link:

    # ln -s /usr/lib/systemd/system/serial-getty@.service /etc/systemd/system/getty.target.wants/serial-getty@ttyAMA0.service

Then connect :)

    # screen /dev/ttyUSB0 38400

## Raspberry Pi camera module

The commands for the camera module are included as part of the raspberrypi-firmware-tools package - which is installed by default. You can then use:

    $ /opt/vc/bin/raspistill
    $ /opt/vc/bin/raspivid

You need to append to `/boot/config.txt`:

    start_file=start_x.elf
    fixup_file=fixup_x.dat

Optionally

    disable_camera_led=1

if you get the following error:

    mmal: mmal_vc_component_enable: failed to enable component: ENOSPC
    mmal: camera component couldn't be enabled
    mmal: main: Failed to create camera component
    mmal: Failed to run camera app. Please check for firmware updates

try setting these values in `/boot/config.txt`:

    cma_lwm=
    cma_hwm=
    cma_offline_start=

## Hardware random number generator

ArchLinux ARM for the Raspberry Pi is distributed with the rng-tools package installed and the bcm2708-rng module set to load at boot (see this), but we must also tell the Hardware RNG Entropy Gatherer Daemon (rngd) where to find the hardware random number generator.

This can be done by editing `/etc/conf.d/rngd`:

    RNGD_OPTS="-o /dev/random -r /dev/hwrng"

and restarting the rngd daemon:

    systemctl restart rngd

Once completed, this change ensures that data from the hardware random number generator is fed into the kernel's entropy pool at `/dev/random`.

## GPIO

### Python

To be able to use the GPIO pins from Python, you can use the RPi.GPIO library. Install either python-raspberry-gpio or python2-raspberry-gpio from the AUR.

## See also

- RPi Config - Excellent source of info relating to under-the-hood tweaks.
- RPi vcgencmd usage - Overview of firmware command vcgencmd.
- Archlinux ARM on Raspberry PI - A FAQ style site with hints and tips for running Archlinux on the rpi

Category:

- ARM architecture