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# Raspberry Pi

From ArchWiki

Summary
Raspberry Pi (RPi) is a minimalist computer built for the ARMv6 architecture. More information about this project and technical specification.
Related
Beginners' Guide RPi Config - Excellent source of info relating to under-the-hood tweaks. RPi vcgencmd usage - Overview of firmware command vcgencmd.

## 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 archlinuxarm documentation.

## Audio

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

Install the needed 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 double MM if muted).

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

## Onboard Hardware Sensors

### Temperature

Temperatures sensors for the board itself are including as part of 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 filesystem:

    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>

- 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

## 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

## Video

    pacman -S xf86-video-fbdev

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.

## Raspberry Pi Camera module

The commands for the camera module are including 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

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